enough toTransportation Engineering - II nissan Planning, design, construction and operation of highways, roads and other vehicular facilities as well as their related bicycle and pedestrian realms. Nissan Foundations Nova Zone, Shambhi Avenue +977-9876543210 +977-01-5544332 1/17/2014 For any correction or suggestion feel free to email or leave reply Email:
[email protected] URL: www.sentientsep.wordpress.com enough to Transportation Engineering - II 2014 Page Numbers mentioned in this Copy are from the Text Book HIGHWAY ENGINEERING by KHANNA and JUSTO eighth edition 2001 softcopy by :- nissan URL » www.sentientsep.wordpress.com 2 notes by Shambhu Kumar Shah enough to Transportation Engineering - II 1. HIGHWAY PAVEMENT Road Pavement A relatively stable layer constructed over the natural soil or soil sub-grade is known as road pavement. - The main function of pavement is to support and transfer the wheel loads of vehicles over a wider area on the underlying sub-grade soil. - A pavement consists of one or more layers, normally sub-grade, sub-base, base course and surface wearing course. (i) Sub-grade: It is an integral part of the road pavement wearing course as it provides the support to the pavement from base course beneath. sub-base (ii) Sub-base: The aggregate/gravel located between soil sub-grade pavement sub-grade and base course to provide fig: layers of pavement additional support in the distributing the stress is called sub-base. (iii) Base course: It is the layer of graded materials located below the wearing course to transfer the stress to the sub-grade through pavement sub-base. (iv) Wearing course: It is the top most layer of pavement, the purpose of which is to provide smooth, abrasion resistant, pressure resistant, water tight and a strong layer. Types of Road Pavement Based on the structural behaviour, road pavements are generally classified into two categories: 1. Flexible pavements 2. Rigid pavements 3. Semi-rigid pavements 1) Flexible Pavement : The pavements which have negligible flexure strength but flexible in their structural action under the loads are known as flexible pavements. - The flexible pavement layers transmit the vertical compressive stresses to the lower layers by grain-to-grain transfer through the points of contact. - The vertical compressive stress is maximum on the pavement surface directly under the wheel load and is equal to the contact pressure under the wheel. - A typical flexible pavement consists of four components: (i) Soil subgrade (ii) Sub-base course (iii) Base course (iv) Surface course softcopy by :- nissan email:
[email protected] 3 II (i) - 2014 Layers of flexible pavement: A typical flexible pavement consists of following four layers: Soil subgrade : The soil subgrade is a layer of natural soil prepared to receive the layers of pavement materials placed over it.com 4 . . In some places boulder stones or bricks are also used as sub-base or soling course. softcopy by :.Wearing course also offers a water tight layer against the surface water infiltration.e. .: a) To improve the load supporting capacity by distributing the load through a finite thickness. The soil subgrade has the lowest stability among the four typical layers of flexible pavement.It resists pressure exerted by tyres and takes up wear and tear due to the traffic.nissan URL » www.The main function of base course is as same as sub-base course i. It is essential that at no time. .In flexible pavement. the purpose of which is to give a smooth riding surface that is dense.Sub-base courses are used to improve the load supporting capacity by distributing the load through a finite thickness. the soil subgrade is overstressed. normally a bituminous surfacing used as a wearing course. (iv) Surface wearing course : The top most layer of pavement is called wearing course. b) To provide a stress transmitting medium to spread the surface wheel loads in such manner as to prevent shear and consolidation deformation. .enough to Transportation Engineering . (iii) Base course : Base course is the layer of broken stone with bound aggregate.wordpress.Sub-base course have no proper interlocking and therefore have lesser resistance to sinking into the weak subgrade soil when wet. (ii) Sub-base course : These layers are made of smaller size graded aggregate / gravel or soilaggregate mixes. . . The loads on the pavement are ultimately received by the soil subgrade for dispersion to the earth mass.sentientsep. notes by Shambhu Kumar Shah enough to Transportation Engineering .II 2) Rigid Pavements : The pavements which have worthy flexural strength are known as rigid pavements.These are normally analysed and designed based on elastic theory assuming the pavement as an elastic plate resting over an elastic plate or a viscous foundation. provided other design factors are same. .The semi-rigid pavements have low resistance to impact and abrasion and therefore are usually provided with flexible pavement surface course. .Higher wheel loads obviously need thicker pavement.It is made up of lean cement concrete. . . . 3) Semi-rigid Pavements : The pavements which have flexural strength in between rigid and flexible pavement are known as semi-rigid pavements. Tandem Axle single axle TRACTOR TRAILER Fig: Wheel Configuration of Tractor Trailer Unit softcopy by :.The rigid pavements have the slab action and are capable of transmitting the wheel load stresses through a wider area below. . reinforced or pre-stressed concrete.) Equivalent single wheel load (ESWL) ii.According to IRC maximum axle load is specified by 8170 kg with a max equivalent single wheel load of 4085 kg.nissan email:
[email protected] 5 .) Contact pressure iv.These are made of plain. soil cement or pozzolanic concrete. Factors Controlling the Pavement Design The various factors to be considered for the design of pavements are: (a) Design Wheel Load: Design of pavement thickness primarily depends upon design wheel load.) Maximum wheel load iii.) Repetition of loads Maximum wheel loads: The wheel load configurations are important to know the way in which the loads of a given vehicles are applied on the pavement surface. . . .The various wheel load factors to be considered in pavement design are: i.The plain cement concrete slabs are expected to take-up about 40 kg/cm2 flexural stresses. the stresses induced are due to the effect of both wheels and the area of overlap is considerable.e.In doing so the effect on the pavement through a dual wheel assembly is obviously not equal to two times the load on any one wheel. .wordpress. .II 2014 Contact pressure: As the depth of pavement increases. S = d + 2a .enough to Transportation Engineering .So the total stresses due to the dual wheels at any depth greater than 2S is considered to be equivalent single wheel load (ESWL) of magnitude ‘2P’. Equivalent Single Wheel Load (ESWL): To maintain the maximum wheel load within the specified limit and to carry greater load. the quality of materials in upper layers should be better as compared to lower layers. it is necessary to provide dual wheel assembly to the rear axles of the road vehicles.com 6 .The intensity of tyre pressure under the wheel is maximum as compared in between wheels. . . .In dual wheel load assembly. then. softcopy by :.At depth 2S and above. as shown in figure. the tyre pressure decrease and finally diminishes at a specified depth.nissan URL » www. .The load dispersion is assumed to be at an angle of 450. d = clear gap between the two wheels S = spacing between the centre of the wheels a = radius of the circular contact area of each wheel.Up to the depth of d/2 each wheel load ‘P’ acts independently and after this point the stresses induced to each load begins to overlap. Hence the material used in different layers are of varying quality i. let.sentientsep. opening. Maintenance cost is more. 3. 2. . Traffic opening after rolling.nissan email:
[email protected] fatigue behaviour of these materials and their durability under adverse conditions of weather should also be give due consideration.Variation in moisture content of subgrade affect the ground water table. affect the performance of the pavement. Maintenance cost is less. 4. Initial cost is more.notes by Shambhu Kumar Shah enough to Transportation Engineering . (c) Climatic Factors: Among the climatic factors. Initial cost is less. surface is worse as compared to rigid pavement. . (e) Environmental Factors: The environmental factors such as height of embankment and its foundation details. (d) Pavement Component Materials: The stress distribution characteristics of the pavement component layers depend on characteristics of the material used. softcopy by :. Design of pavement is done with 8. 2. 6. depth of cutting. Its life is up to 20 yrs. 1.Where freezing temperatures are prevalent during winter. Can be done in stage construction. . . 3. 8. Minimum 28 days requires for traffic 6. More hazardous to the environment. The characteristics of pavement 5.A subgrade with lower stability requires thicker pavement to protect it from traffic loads. drainage conditions.The daily and seasonal variation in temperature has significance in the design and performance of rigid pavements and bituminous pavements. the possibility of frost action in the subgrade and the damaging effects should be considered at the design stage. 7. Design of pavement is done with accuracy.com 7 . depth of subsurface water table etc. 7. less accuracy.II (b) Subgrade Soil: The properties of soil subgrade are important in deciding the required thickness of pavement. type of pavement and shoulders. 4. 5. Less hazardous to environment. The characteristic of pavement surface are good. Comparison between Rigid pavement and Flexible pavement Rigid pavement Flexible pavement 1. Its life time is up to 40 yrs. rain fall affects the moisture condition in the subgrade and the pavement layers. . It is done at a time. softcopy by :. Burmister method iii. .Hence the superior pavement materials are used in top layers of flexible pavement. Out of various flexible pavement design methods available. In the design process. Steel in 1945 provided a discussion on the paper dealing with the Highway Research Board method of soil classification which included the suggested thickness requirements based on Group Index (GI) values.J.The GI values of soils vary in the range of 0 to 20. ii. . weaker the soil subgrade and for a constant value of traffic volume.wordpress. under the application of load none of the layers is overstressed. Stabilometer method vii. CBR (California Bearing Ratio) method: The CBR tests were carried out by the California State Highway Department on existing pavement layers including subgrade. McLeod method ii.sentientsep. diameter (iii) Dial gauges Procedure: Soil subgrade specimen is placed in mould in four layers. . Triaxial test method i. .A surcharge load equal to the water absorbed values are applied along with the plunger on the top of specimen. . the following are some common methods: i.The maximum intensity of stresses occurs in the top layer of the pavement and magnitude of loads stresses reduces at lower layer. it is to be ensured that. . CBR (California Bearing Ratio) method vi. This method is done in two steps: (a) Calculation of CBR value: It consists of following apparatuses: (i) 150 mm diameter mould with base plate (ii) Loading frame having cylindrical plunger of 50 mm. Group index method: D. . after soaking and swelling. the greater would be the thickness requirement of the pavement.II 2014 Method of Flexible Pavement Design The flexible pavements are built with number of layers. Group index method v. Asphalt institute method iv.This means that at any instance no section of the pavement structure is subjected to excessive deformation to form a localised depression or settlement.enough to Transportation Engineering .com 8 .The higher the GI values.nissan URL » www.The water absorption values are noted. sub-base and base course. 0.5 and 5. cm2 ( ) iv. 3. Triaxial test method: The triaxial compression test is used in determining the values of elastic moduli for various materials. 0. 2. X Y Tp P Es Ep Δ a = = ) -( ) ⁄ = thickness of pavement = wheel load (kg.0.5 and 12. 1. McLeod through Canadian Department of Transport conducted extensive plate bearing tests on airfield and highway pavements and developed a design method. .5.The CBR value is calculated by using the relation: ( ) .25 mm/minute and the load values are noted corresponding penetration values of 0.√( Where.enough to Transportation Engineering . % P = tyre pressure.5.II notes by Shambhu Kumar Shah .0.5 mm.The standard load values obtained from the average of a large number of tests on crushed aggregates are 1370 and 2055 kg (70 & 105 kg/cm2) respectively at 2.com 9 . McLeod method: Norman W. 4. kg/cm2 A = area of contact.The load is applied at 1. 2. kg CBR = California Bearing Ratio.The repetitive bearing test procedure was employed using various sizes of plates.) = modulus of elasticity of subgrade in kg/cm2 = modulus of elasticity of pavement materials = deflection = radius of contact area (cm) traffic coefficient rainfall coefficient v. cm P’ = wheel load.0.nissan email: passurexam@yahoo. . t = pavement thickness. 7.5. The pavement thickness (Tp) is calculated from the relation: . Where. (b) Calculation of thickness of pavement: The thickness of pavement is obtained by using the formula:⁄ √ [ ] [ ] This expression is applicable only when the CBR value of the subgrade soil is less than 12%.0 mm penetration. softcopy by :.0. 1. Mr + = equivalent elastic modulus = 10 × CBR Stresses due to Load.nissan URL » www. Burmister’s (Layered System) method: The total mass of pavement and subgrade does not possess a constant E value as assumed by Boussinesq’s analysis.75 Four lane 15 m . calculated for 30 cm dia.4 iii) Growth factor = ( ) iv) Calculate the thickness from chart.5 m 1. T P S = = = required thickness of gravel base. Since. the flexible pavement sections are composed of layers and the elastic modulus of the top layer is the highest. sub-base course and base course are assigned elastic moduli of Es. * Where. form formula.75 m 2 Intermediate lane 5. plate at 0. softcopy by :. it is considered Es = Esb = Eb.II 2014 From the plate load tests an empirical design equation was recommended: Where. Asphalt institute method: Design Procedure: i) Calculate the equivalent single axle load (EASL) over the design life = estimated traffic at the base period × growth factor × no.5 cm vi.If the layers of soil subgrade. cm gross wheel load. where as in layered analysis. of axles × lateral displacement factor ii) Lateral displacement factor (LDF) for various lane: Lane Width LDF Single lane 3.com 10 . of working days × no.5 Two lane 7m 0.sentientsep. it is taken that Eb > Esb > Es.wordpress. v) Equivalent thickness. edge or in between both. Some of the researchers have given single empirical formula while some of them have given according to position.enough to Transportation Engineering . vii. Temperature differential & Subgrade friction on Rigid pavement: (i) Stresses due to Load: The position of wheels of the vehicles are not constant. . these may be located at corner. Eb then as per Boussineq’s analysis. Esb. kg total subgrade support in kg. stress at interior.com 11 . [ (b) Edge loading.Since the slab is in contact with soil subgrade or the sub-base. .II notes by Shambhu Kumar Shah i.) According to A-T Goldback: Stress load due to corner load (Sc) is given by: Where. Sc = max.The variation in temperature across the depth of slab is caused by daily variation whereas an overall increase or decrease in slab temperature is caused by seasonal variation in temperature. as the mean temperature of the slab increases. the slab movements are restrained due to the friction between the bottom layer of the pavement and the soil layer. edge & corner loading (kg/cm2) h = slab thickness (cm) P = wheel load (kg) a = radius of wheel load distribution (cm) ℓ = radius of relative stiffness (cm) b = radius of resisting section (cm) (ii) Stresses due to Temperature differential: Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. the slab contracts causing tensile stress at the bottom due to frictional resistance.During summer season. . . compressive stress is developed at the bottom of slab as it tends to expand. (c) Corner loading. there is an overall expansion and contraction of the slab. the concrete pavement expands towards the expansion joints.nissan email: passurexam@yahoo. . ( ⁄ ) [ ( ⁄ ) ( √ ) ] ] ] Where. Se. (iii)Stresses due to Friction: Due to uniform temperature rise and fall in the cement concrete slab. Sc P h = = = stress due to corner load (kg/cm2) corner load assumed as a concentrated thickness of slab (cm) ii.This frictional resistance therefore tends to prevent the movements thereby inducing the frictional stress in the bottom fibre of cement concrete pavement.Similarly during winter season. . Si. Due to frictional resistance at the interface. softcopy by :.enough to Transportation Engineering .) According to Westergaard’s: The critical stresses at different locations are given by: [ (a) Interior loading. wordpress. (kg/cm3) ⁄ ) {about 2400 kg/m3} Combination of Stresses: The stresses developed due to different reasons should occur at a time or separately.) During Winter: The critical combination of stresses at the above regions occurs at the bottom fibre during the midday when the slab tends to warp downward.During this period maximum tensile stress is developed at bottom fibre due to warping and this is cumulative with the tensile stress due to the loading.Since the differential temperature is of lower magnitude during winter than in summer. Critical stress = load stress + warping stress – frictional stress ii.Critical stress combination = Load stress + Warping stress + Frictional stress .e. k= ⁄ Where. iii. .enough to Transportation Engineering . W = unit wt. of concrete.nissan URL kg/cm2 » www. i.The upward reaction at any point is assumed to be proportional to the deflection at that point. when the slab tends to warp upward. the Rigid Pavements are made of cement concrete.II 2014 .Rigid pavements should be analysed by Plate theory instead of Layered theory. k = modulus of subgrade reaction P = pressure sustained (kg/cm2) Δ = displacement level (taken as 0.com 12 .Critical stress combination = Load stress + Warping stress Design of Rigid Pavements Since. . i. The following critical combinations are considered. .) During Summer: The critical combination at interior and edge regions during midday occurs when the slab tends to warp downward.Unit stress developed in cement concrete pavement is given by: ( Where. P=kΔ Or.However. .sentientsep. .125 cm) k= ⁄ softcopy by :. frictional stress is compressive during monsoon. the load carrying capacity is mainly due to the rigidity and high modulus of elasticity of slab. Westergaard’s Analysis Westergaard considered the rigid pavement as thin elastic resting on liquid foundation.) At the corner region the critical combination occurs at the top fibre of slab during the midnight. . the combination (i) is worst for most of region of the country. warping stress is given by: ( ) ( ) √ Where. stresses in Rigid pavement: 1.For the corner region.The resultant deflection of the slab which is also the deformation of subgrade is a direct measure of the magnitude of subgrade pressure.com 13 . ℓ = radius of relative stiffness (cm) E = modulus of elasticity of cement concrete (kg/cm2) μ = Poisson’s ratio for concrete [ = 0. .The difference in temp between the top and bottom of the slab depends mainly on the slab thickness and the climatic conditions of the region.nissan = modulus of elasticity of concrete (kg/cm2) email: passurexam@yahoo. .II notes by Shambhu Kumar Shah Relative stiffness of slab to subgrade: A certain degree of resistance to slab defection is offered by the subgrade. . Warping Stresses: Whenever the top and bottom surfaces of a concrete pavement simultaneously possess different temperature.The pressure deformation characteristic of rigid pavement is thus a function of relative stiffness of slab to that of subgrade.The variation in temp. . across the depth of the slab is caused by daily variation whereas an overall increase or decrease in slab temperature is caused by seasonal variation in temp. .enough to Transportation Engineering . E softcopy by :.15 ] h = slab thickness (cm) k = subgrade modulus or modulus of subgrade reaction (kg/cm 3) Temperature stresses in Rigid Pavement Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. the slab tends to warp downward or upward inducing warping stresses. . Warping stresses 2. Westergaard defined this term as the Radius of relative stiffness: ⁄ * + ( ) where. This is dependent upon the stiffness or pressure-deformation properties of the subgrade material.Following are the types of temp. .The tendency of the slab to deflect depends upon its properties of flexural strength. Frictional stresses 1.The warping stress at the edge region is given by: (whichever is higher) ( ) . . IRC recommendations for design of rigid pavements: Design Parameters: The design wheel load is taken as 5100 kg with equivalent circular area of 15 cm and tyre inflation pressure ranging from 6.e.II e t Cx Cy μ a ℓ 2014 = thermal coeff.com 14 . of concrete per degree Celsius = temp.Unit stress developed in cement concrete pavement is given by: Where. The flexural strength of cement concrete used in the concrete should not be less than 40 kg/cm2. of concrete.enough to Transportation Engineering .Hence. frictional stress developed is higher due to the greater movement i.3 kg/cm2.3 to 7. stress induced due to this. there is overall expansion and contraction of the slab. (kg/cm3) {about 2400 kg/cm3} f = coefficient of subgrade restraint L = slab length in m. is negligibly small whereas in long slab.sentientsep. A = P ( 1 + r ) n + 20 ( in CV / day ) The mean daily and annual temperature cycles are collected.15 ) = radius of contact = radius of stiffness 2.Since the slab is in contact with soil subgrade or the sub-base. - - W = unit wt. Traffic volume. 1. based on ⁄ in right angle to above direction = Poisson’s ratio ( 0.15 cm. . difference between top & bottom of slab in 0c = coefficient based on ⁄ in desired direction = coeff. Calculation of Stresses: . slab movements are restrained due to the friction between the bottom layer of pavement and soil layer.The temperature stress at edge is calculated as per Westergaard’s Analysis. Frictional Stresses: Due to uniform temperature rise and fall in the cement concrete slab. . the frictional resistance is induced in bottom fibre of the pavement. . B = slab width in m.wordpress. softcopy by :.In short slab.The wheel load stresses at the edge and corner region is calculated for the designed slab thickness as per Westergaard’s Analysis. . 2.nissan URL » www. 0. It is used across the longitudinal joint of cement concrete pavements. Design steps of Slab thickness: . Half-length of this bar is bonded in one cement concrete slab and the remaining portion is embedded in adjacent slab. . .5m in unreinforced slab of all thickness and for reinforced slab. but is kept free for the movement during expansion and contraction of the slab.The total stresses at the corner due to wheel load and warping is checked for slab thickness (h cm). .The width of slab is decided based on joint spacing and lane width. 4.The length of cement concrete slab is equal to the spacing of contraction joints. for all slab thickness. The warping stress at edge region is calculated and this value is subtracted from allowable flexural stress in concrete to find the residual strength in the pavement to support edge loads. softcopy by :.The maximum contraction joint spacing may be kept at 4.II 3. . Spacing of joints: . Design of Dowel bars: Dowel bars of expansion joints are mild steel round bars of short length.When the foundation surface is smooth.A trial thickness of slab is assumed for calculation the stresses. 5. Tie bars ensure two adjacent slabs to remain firmly together.notes by Shambhu Kumar Shah enough to Transportation Engineering .The load stress in edge region is found. . b) Maintaining the slab edge at the same level. . 6. c) Load transference is affected from one slab to the other.The maximum spacing recommended for 25 mm wide expansion joints is 140 m when the foundation is rough.The main function of dowel bar is:a) Allow opening and closing of the joint.r.The design thickness (h) is adjusted for the traffic intensity or classification at the end of design life and using the adjustment value from table recommended by IRC to obtain the final adjusted slab thickness. Design of Tie bars: Tie bars are made of mild steel deformed bars of limited length.nissan email:
[email protected]. The available factor of safety in edge load stress w. .com 15 . Spacing may be 90m for slab thickness up to 20cm & 120m for slab thickness up to 25cm. the residual strength is found. it may be 13m for slab thickness 15cm. . sentientsep.com ⁄ 16 .II 2014 Numericals Design a flexible pavement.07)10+2 = 290. thickness of wearing course = 50 mm Thickness of base course = 130 – 50 = 80 mm # Design a flexible pavement by using Asphalt Institute method from the following data of a stretch of existing two lane road. page no. Pavement will have bituminous surfacing. Solution: No.nissan ) URL ( ) » www. CBR of subgrade is 5%. and the maximum life of the pavement is 10 yrs.07 Construction period. n = 10 yrs. of CV/day. Construction period = 16 months CBR value of subgrade = 5 % Elastic modulus of Asphalt Concrete surface course = 2500 MPa Elastic modulus of bituminous treated base course = 1200 MPa Elastic modulus of granular sub-base course = 125 MPa Solution: Estimated traffic at the end of design life = estimated traffic at base period × growth factor × no. of working days × no.53 291 cv/day From Chart 7.11 (CBR Design Chart.enough to Transportation Engineering . curve D is chosen From Curve D. Correct traffic of 80kN equivalent single axle load=0. Total thickness over sub-base = 130mm (base + surface course) Actual thickness of sub-base = 380 – 130 = 250 mm Adopting. y = 2 yrs. A = P (1 + r) n + y = 129 (1 + 0. 351) For A = 291. of axles × lateral displacement factor Where. number of commercial vehicles per day for design is given by. Base material has CBR value of 80%. Design life of pavement.wordpress. r = 0. ( softcopy by :.95×103 ESAL/day Traffic growth rate = 7.5 % Design period = 15 yrs. for CBR = 5% (subgrade) Total thickness of pavement over the subgrade = 38 cm = 380 mm For CBR = 30%. The compacted sub-base poorly graded gravel layer has a CBR value of 30%. P = 129 cv/day Annual growth. Now. if 129 CV/day (commercial vehicles per day) exists and growth rate is 7% construction period of the pavement is 2 yrs. Solution: [( ) ] [ ] Here.enough to Transportation Engineering . 5 P = 1000 CV/day n =15 [( ) ] [ ] Design a highway pavement for a wheel load of 4100 kg with a tyre pressure of 5 kg/cm2 by McLeod method.5 kg/cm2 after 10 repetition of load at 0. Calculate the standard axle to be used in design. 2-way road is at present carrying traffic of 1000 CV/day at plain terrain. 0. ⁄ ⁄ ( ) ( ) A 2-lane. Mr = 50 MPa and 1. Equivalent thickness of bituminous treated base course.II notes by Shambhu Kumar Shah Estimated traffic at the end of design life = 0. ⁄ ⁄ ( ) ( ) For sub-base course. VDF LDF r y = = = = 2. period of construction is 5 yrs. Solution: Radius of contact (a): √ softcopy by :.10 ×365 ×2 ×0.com 17 .75.57 * 107 ESAL/day Full depth of asphalt concrete = 390 mm Use of AC surface course = 75 mm Remaining depth of asphalt concrete = 390 – 75 = 315 mm Use 200mm base course and 115mm sub-base course.95 * 103 ×30.75 = 1. the pavement is to be designed for 15 years after construction. For base course.5 cm deflection.5 0. plate yielding a pressure of 2.nissan email: passurexam@yahoo. Resistant modulus (Mr) = 10 × CBR = 10 × 5 = 50 MPa From graph. The plate bearing carried out on sub-grade soil using 30 cm dia. The rate of growth of traffic is 10% per annum. Equivalent thickness of granular sub-base.1.57 * 107 ESAL/day We have. k = 89 Required thickness of gravel base. The ratio of unit subgrade support on 32.20 (page 367).5cm deflection = 0.19 Required thickness of gravel base. ⁄ Using Chart 7. as 89 I.44 kg/cm2 Design sub-grade support on 32. Base course constant for 30.5cm deflection = 0. plate is obtained as 90.wordpress.95 Unit support at 0.2 cm dia. Base course constant (k) for 32.4 cm dia.2cm dia. # softcopy by :.4cm dia.99 × 2.5 = 2. ⁄ Using Chart 7.5mm by McLeod method.com 18 . # Plate bearing test conducted on subgrade soil using 30cm diameter plate yielded 2. plate at 0.19.5cm deflection is 0.nissan URL » www. plate is obtained from chart 7.5cm deflection is 0.enough to Transportation Engineering . plate. plate.2cm dia. Design a highway pavement for a wheel load of 5100 kg and tyre pressure of 7 kg/cm2 for allowable deflection of 7.5 = 2.5 kg/cm2 after 10 repetitions at 5mm deflection. Provide 5cm of bituminous surfacing out of this thickness.sentientsep. Provide 5cm of bituminous surfacing out of this thickness.4cm dia. plate at 0. from graph 7.95 × 2.99 Unit support at 0.II 2014 Perimeter over area ratio. (Refer charts). Solution: Radius of contact (a): √ Perimeter area ratio.48 kg/cm2 Design sub-grade support on 30. The ratio of unit subgrade support on 30.20 (page 367).e. 0 67.0 10. The following were the result.2 5.5 12.0 2.5 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Penetration (mm) → softcopy by :.5 1.5 It is desired to use following materials for different pavement layers. Traffic survey revealed present ADT of commercial vehicles as 1200.0 99.5 0.0 30 20 2.0 4.5 48.0 75.0 56.5 5. mm Load. Solution: The plot is made between loads (kg) vs. b) Suggest design without use of poorly graded gravels.5 2.5 89. penetration (mm).II notes by Shambhu Kumar Shah Soil sub grade sample was obtained from the project site and CBR test was conducted at field density.nissan email: passurexam@yahoo. The pavement construction is to be completed in three years after last traffic count.0 16.5 28. Annual rate of growth of traffic is found to be 8%.2 1. kg 0.0 3. a) Design pavement section by CBR method as recommended by IRC.0 0. Compacted sandy soil with 7% CBR Poorly graded gravel with 20% CBR Well graded gravel with 95% CBR Minimum thickness of bituminous concrete surfacing may be taken as 5cm. 110 100 90 80 Load (kg) → 70 60 50 40 5.0 40.1 7.com 19 13 .enough to Transportation Engineering . Penetration (mm) Load (kg) Penetration.5 106. A= P (1 + r) n + 10 = 1200 [ 1 + ] 3 + 10 = 3260 vehicles/day 55 cm 21 cm 8 cm Bituminous surfacing ↕8cm 13 cm Well graded gravel. CBR = 4 % 40 cm For A = 3260 vehicles/day. A = π × Pressure at 2.5mm penetration = Adopt CBR value = 4 % Calculation for design thickness of different layers: No.9 softcopy by :. Pavement thickness required = 21 cm Well graded gravel with 95 % CBR Pavement thickness required = 8 cm # Design the pavement section by triaxial test method using the following data: Wheel load = 4100 kg Radius of contact area = 15 cm Traffic coefficient. design curve F is used (from fig.5 Rain fall coefficient.6 cm2 kg/cm2 ⁄ Similarly.11. Pressure at 5mm penetration = kg/cm2 CBR values of soil at. Total pavement thickness over subgrade = 55 cm Compacted sandy soil with CBR = 7 % Pavement thickness above compacted subgrade = 40 cm Poorly graded gravel with 20 % CBR.nissan URL » www. Area of plunger of dia. CBR = 20 % 15 cm Compacted soil. X = 1.wordpress.5 mm penetration = = 19. of vehicles for design.enough to Transportation Engineering . for CBR = 4 %. 7.com 20 . CBR = 95 % 19 cm Poorly graded gravel. CBR = 7 % Soil subgrade. page 351) From curve.sentientsep. (d) 5cm is. 2.II 2014 From graph. Y = 0. Load at 2.5 & 5 mm penetration (after correction) are 55 & 78 kg resp. the pavement thickness is given by: ⁄ {√( ) }( ⁄ {√( ) ) }( ) = 65.II notes by Shambhu Kumar Shah Design deflection. Eb = 400 kg/cm2 E-value of 7.nissan ⁄ = 0. Eb = 400 kg/cm2 63.2 cm [ Soil subgrade.: ⁄ ] [ ] Required thickness of base course ( ) = 55. Δ = 0.2 7.5 cm thick bituminous concrete surface course = 1000 kg/cm2 Solution: Assuming the pavement to consist of single layer of base course material only.74) √ email: passurexam@yahoo. edge and corner regions of a cement concrete pavement using Westergaard’s stress equation. Use the following data: Wheel load.5 cm Bituminous surfacing ↕7. Ec be equivalent to the thickness tb of base course. μ = 0.5 cm bituminous concrete surface course. i.7 cm Base course. k = 6 kg/cm3 Radius of contact area. P = 5100 kg Modulus of elasticity of cement concrete. # = 65. a = 15 cm Solution: Radius of relative stiffness (ℓ ) is given by: ⁄ ⁄ * ( ) + * ( ) + The equivalent of resisting section is given by: ⁄ √ softcopy by :.5cm 55.9 cm Here. Es = 100 kg/cm2 E-value of base course material.833 (< 1. h = 18 cm Poisson’s ratio of concrete. Es = 100 kg/cm2 # Calculate the stresses at interior.7 cm. E= 3 × 105 kg/cm2 Pavement thickness.15 Modulus of subgrade reaction.25 cm E-value of subgrade soil. Ec = 1000 kg/cm2 Let.enough to Transportation Engineering .com 21 .e.9 – 10. E-value for 7. com ⁄ ⁄ ] 22 . * [ ( ( ⁄ ) ⁄ ) + ] Stress at the edge. Radius of relative stiffness.5 m Now. μ = 0. ⁄ ⁄ * ( ) + ( [ ⁄ Here.sentientsep.enough to Transportation Engineering .5 % v) Temperature variation.10C vi) Modulus of sub-grade reaction. E = 3 × 105 kg/cm2 ix) Poisson’s ratio.5 m Lane width (w) = 3. t = 13.15 x) Coefficient of thermal expansion (α) = 10 –5 /0C Solution: Trial 1: Select the thickness of slab (h) = 20 cm (20~25) Contraction joint spacing (L) = 4.II 2014 Stress at interior region. k = 6 kg/cm3 vii) Concrete flexure strength = 40 kg/cm2 viii) Modulus of elasticity of concrete. softcopy by :. [ ( √ ) ] [ ( √ ) ] Design a cement concrete for the following condition: i) Design wheel load = 4100 kg ii) Present traffic = 300 CV/day iii) Design life = 20 yrs.wordpress. iv) Traffic growth rate = 7.nissan * URL ) + ⁄ » www. * [ ( ( ⁄ ) ⁄ ) + ] Stress at the corner. edge load stress (Se) is obtained from Chart 7.25.87 kg/cm2 For.com 23 .9.6. ok. h = 23 cm and k = 6 kg/cm2. page 377) 2 < 40 kg/cm . ( ) Residual strength of concrete. Cy = 0.9 For = 4. page 376) = 1. For = 5. ( ( ) ) Residual strength of concrete. Design traffic volume = P (1 + r) n = 300 (1 + From chart. Corner load stress (Sc).77 (From chart 7. Edge temperature stress. = Flexure strength – Edge temp stress = 40 – 17. = Flexure strength – Edge temp stress = 40 – 15. edge load stress (Se) = 24 kg/cm2 Available factor of safety = ⁄ (from Chart 7. not safe.23. page 380).69 = 22. Now.13 = 24.23 (page 376) Se = 29 kg/cm2 Available factor of safety = = 0.65 Use.31 kg/cm2 For.769 < 1.24.II notes by Shambhu Kumar Shah From chart 7. # softcopy by :.nissan email: passurexam@yahoo. Trial 2: Try.29.25 (page 380). h = 23 cm ⁄ ⁄ * ( ) + * ( ) + ⁄ For ⁄ = 5. for h = 23 cm and k = 6 kg/cm2 Sc = 24 kg/cm2 (from chart 7. ht = 0 h = hs + ht = 23 + 0 ⁄ ) 20 = 1275 = 23 cm So. Cx . Cx > C y Edge temperature stress. Cx = 0.04 > 1.enough to Transportation Engineering . ok. h = 20 cm and k = 6 kg/cm2. Adopt slab thickness = 23cm. Cx = 0. II softcopy by :.sentientsep.enough to Transportation Engineering .nissan URL » www.com 2014 24 .wordpress. ) Lifting equipment: i) Backhoe → to lift construction materials to certain heights ii) Crane → to lift construction materials as per crane type softcopy by :.) Earth moving equipment: i) Bull dozer.II 2. ROAD CONSTRUCTION TECHNOLOGY Tools. soil etc. v) Impact rammer → used in small area. where difficult to operate other equipment. sand & aggregate v) Bituminous pavers vi) Cement concreter pavers 5. Scrapper → shallow excavation ii) Power shovel → excavation in soft and medium soil iii) Dragline → to excavate soft soil iv) Clamshell → excavation in soft and medium soil v) Excavator → for excavation work vi) Trench digger → for deep excavation 2.) Levelling equipment: i) Grader → to make surface of certain gradient 3. crust. 4. Equipment: 1. Equipment and Plants used in Road construction A.) Paving equipment: i) Binder spreader → to spread the binder ii) Aggregate spreader → to spread aggregate iii) Heating kettle for binder iv) Cement concrete mixer → to mix cement.nissan email:
[email protected] by Shambhu Kumar Shah enough to Transportation Engineering .com 25 . Tools: i) Hand shovel → for excavation in soft soil ii) Peak → for excavation in hard soil iii) Chisel → for excavation in hard soil iv) Hand rammer → for compaction v) Brushes → for cleaning vi) Wheel barrow → for carrying materials vii) Trowel → for mixing of mortar and masonry B.) Compaction equipment: i) Vibrating roller → in cohesion less soil ii) Pneumatic roller → in cohesive and cohesion less soil iii) sheep’s foot roller → in cohesive soil iv) Smooth wheel roller → for granular soil like gravel. Not needing manpower for unloading.wordpress.nissan URL » www.) Hoe: Hoe is meant to excavate below the natural surface where the machine is stationed. .Bulldozer is suitable for clearing site.enough to Transportation Engineering . hauling and discharging the material in uniformly thick layer. FA and binders iv) Aggregate crusher plant → breaking stones as per size of aggregate v) Washing plant → to wash aggregate vi) Screening plant → to screen aggregate Earth excavation equipment and their suitability i. iii.) Clamshell: This equipment is useful for excavation of soft to medium materials and loose materials at or below existing ground surface.The power shovel can effectively operate to excavate earth from lower level when the depth of the face to be excavated is not too shallow. ii.It can exert high tooth pressure and hence can excavate stiff materials which normally can’t be excavated by dragline. v.II 2014 6. .Scrapper is suitable for digging. ii) Trucks → to shift the construction materials in large quantity and longer distances. iii) Mini dumpers → to shift the construction materials in small quantity and shorter distances.) Drag line: Dragline is suitable to excavate soft earth and to deposit in nearby or to load into wagons. fine aggregates and binders iii) Cold premix mixing plant → mixing of CA. opening up pilot roads and hauling earth for short distance about 100m.) Bulldozer & Scraper: These are used for shallow excavation work and for hauling the earth for relatively short distances.) Transporting equipment: i) Dumping trucks (Tipper) → to shift materials. softcopy by :.) Power shovel: It is primarily used to excavate earth of all classes except rock and to load it into wagons. . iv.com 26 . Plants: i) Cement concrete plant → mixing cement concrete ii) Asphalt concrete cement → mixing of course aggregate.sentientsep. . C. transporting & dumping it as a fill or spoil bank.II Activities and Techniques used in Road Construction Following activities and techniques are used as per nature. soft rock or even in hard rock. the grading operation is started so as to bring the vertical profile of the subgrade to designed grade and camber. roots. . rubbish and other organic matter should be removed. . softcopy by :.Earth excavation work may be divided as excavation or cutting. Next. Excavation It is the process of cutting or loosening & removing earth including rock from its original position. grading (embankments or cut) and compaction. 1) Bulldozer & Scraper: (i) Site clearance (iv) Excavation for borrow pit (ii) E/W in filling for embankment (v) Excavation for structural (iii) Excavation for cutting foundations (vi) Disposal of surplus earth 2) Drainage works: (i) Minor bridges (iii) Side drains (ii) Causeways (iv) Culverts 3) Protection works: (i) Earth retaining structures (iv) Landslide stabilisation (ii) Slope protection works (v) Bridge protection works (iii) Gully control works 4) Pavement works: (i) Subgrade preparation works (iii) Base works (ii) Sub-base works (iv) Surface works 5) Miscellaneous works: (i) Road ancillaries (iii) Bio-engineering works (ii) Traffic works (iv) Information works for traffic & pedestrians Various works for Road construction - Preparation of subgrade Subgrade is the lower most portion of the highway construction. grading and compaction. It may be situated on embankment or excavation or at existing ground surface. In all the cases.notes by Shambhu Kumar Shah enough to Transportation Engineering . site should be cleared off and top soil consisting grass. type of work and elements of road to be constructed. before preparing subgrade.com 27 .nissan email: passurexam@yahoo. It is most essential to compact the top of the subgrade adequately before placing the pavement layers.The excavation or cutting may be needed in soil. The preparation of subgrade includes site clearance. by Swedish Circular Arc Analysis etc.sentientsep.enough to Transportation Engineering . consequently cracks may appear after application of load through vehicles and hence it may failure.5. the foundation stability is evaluated & factor of safety is estimated by various approaches.com 28 . .r.II 2014 Fill / Embankment When it is required to raise the grade line of a highway above the existing ground level.nissan URL » www. iii) To maintain the design standard of highway w.Hence the stability of the slope should be checked or the slope should be designed providing minimum factor of safety of 1.t. softcopy by :. .If the embankment foundation consists of compressible soil with high moisture content. . the consolidation can occur due to the increase of load and the embankment may be failure. in case of compressible soil foundation should be minimum just after the completion of the embankment.wordpress. Remedial measures: Such problems can be eliminated by following ways: (i) Stability of foundation (ii) Stability of slopes i) Stability of foundation When the embankment foundation consists of weak soil just beneath or at a certain depth below in the form of weak stratum. E. ii) Stability of slopes The embankment slopes should be stable enough to eliminate the possibility of a failure under adverse moisture and other conditions.For this. . .Flatter slopes are preferred due to aesthetic or other reasons.g.The factor of safety. The grade line may be raised due to following reasons: i) To keep the subgrade above the high GWT.The settlement of fill is generally due to inadequate compaction during construction. it becomes necessary to construct embankments. Following are the design elements of highway embankments: a) Height d) Stability of foundation b) Fill material e) Stability of slopes c) Settlement Problems in the construction of high embankment The embankment may settle after the completion of construction either due to consolidation and settlement of the foundation or due to the settlement of fill or due to both. vertical sand drain should be constructed to increase the rate of gain in strength for compressible soil foundations. ii) To prevent damage to pavement due to surface water & capillary water. . it is essential to consider the stability of the foundation against a failure.Also. . the vertical alignment. It is suitable to compact non-plastic silts and fine sands.The gross weight of such roller ranges between 4 to 18 tons.It is more suited to compact clayey soil.notes by Shambhu Kumar Shah enough to Transportation Engineering . which would give maximum dry density for a particular type and amount of compaction. reduces settlement and lowers the adverse effects of moisture.There are also vibrator mounted roller to give combined effects of rolling and vibration. . (iii) Vibrators These are most suited for compacting dry cohesion less granular material. . under a loading platform. (a) Smooth wheeled roller The smooth wheeled rollers are suitable to roll wide ranges of soils. a number of pneumatic wheels are mounted on two or more axles. . (iv) Watering (jetting & ponding) It is considered to be an efficient method of compacting cohesion less sand.nissan email:
[email protected] increases the density and stability.It is well known fact that there is an optimum moisture content (OMC) for a soil. .II Compaction It is a mechanical process by which air is expelled out from soil mass to reduce the void and to make the soil dense. (b) Pneumatic tyred roller In this type of roller. which is slowly increased and then decreased. . preferably granular soils and pavement materials for the various layers. softcopy by :. .About 24 or more number of passes of the roller may be necessary to obtain adequate compaction.com 29 . (ii) Rammers These are useful to compact small areas and where the rollers can’t operate such as compaction of trenches. Factors affecting compaction i) Moisture content ii) Amount of compaction iii) Type of compaction iv) Soil type v) Addition of admixture Compacting Equipment Following are the various types of compacting equipment: (i) Roller The principle of rollers is the application of pressure. foundations and slopes. (c) Sheepsfoot roller Roller consists of hollow steel cylinder with projecting feet. . the desired value of which may be achieved by increasing the number of passes for the selected equipment and thickness of each layer. .If the stability of local soil is not adequate for supporting wheel loads. sand replacement method is considered quite satisfactory.t. stability. the density of soil starts decreases. w = unit wt. = moisture content = unit wt.As the water content increases further beyond this limit.com 30 . of soil Soil Stabilisation Soil stabilisation is a method of improving the qualities of inferior soil w. it is essential to have proper field control in compaction.Dry density may be found by any suitable method i.r.sentientsep.II 2014 Field Control for Compaction For adequate quality control in construction.nissan URL » www.wordpress. . Following are the techniques of soil stabilisation: (a) Proportioning technique (e) Water repelling agent (b) Cementing agent (f) Heat treatment (c) Modifying agent (g) Chemical stabilisation (d) Water proofing agent softcopy by :. then the next control is the dry density. density. This limit is known as optimum moisture content (OMC). strength.enough to Transportation Engineering . compaction curve OMC Moisture content → The theoretical relationship between moisture content and dry density is: Where. of soil solids.e.If the moisture is controlled at the OMC. . the properties are improved by soil stabilisation techniques. . . Following are two field control tests: (i) Measurement of moisture content (ii) Measurement of dry density The moisture content of the soil may be found before compaction by any one of the rapid method suitable at the site. Dry density → Moisture density relationship Density of soil increases with increase in water content up to certain limit.A certain percentage (≈ 95 or 100 %) of the standard density is generally aimed at in the field compaction. bearing capacity etc. but it is not very suitable under freezing temperature. cement and water are mixed and well compacted to form a strong base course. as the material has poor resistance to abrasion and impact. . soil. (iii) Soil-lime stabilisation Soil-lime has been widely used either as a modifier for clayey soil or as a binder. .Soil-lime is quite suitable as sub-base course for high types of pavements and base course for pavements with low traffic. there is an increase in the strength and durability of soil-cement and a decrease in volume change. the method is called mechanical stabilisation. having less affinity with water.When clayey soils with high plasticity are treated with lime. . the plasticity index is decreased and the soil becomes friable and easy to be pulverised.It is also quite suitable in warm regions. . this can’t be used as a surface course.notes by Shambhu Kumar Shah enough to Transportation Engineering .By the increasing percentage of cement added. (iv) Soil-bitumen stabilisation The basic principles in bituminous stabilisation are water proofing and binding. .II Method of Soil Stabilisation (i) Mechanical soil-stabilisation Correctly proportioned construction materials (aggregate and soil) when adequately compacted to get a mechanically stable layer.nissan email: passurexam@yahoo. moisture movement and plasticity. . . .Most commonly used materials are cutback and emulsion. softcopy by :. .The two basic principles in this method are: (a) proportioning (b) compaction .Soil-cement stabilisation can be used as a sub-base or base course of all type of pavements.However.Mechanical stabilisation has been successfully applied for sub-base and base course and also used as surface course for low cost roads. (ii) Soil-cement stabilisation In this method.By water proofing the inherent strength and other properties of soil could be retained.Bituminous stabilised layer may be used as a sub-base or base course of ordinary roads and even as surface course for roads with low traffic in low rainfall regions. .com 31 . The crushed stone aggregate should be generally hard.sentientsep. loose materials etc.II 2014 Construction of Water Bound Macadam (WBM) Roads 1) General The term Macadam is the present day means. base course or surfacing course. durable and of acceptable shape. Its thickness for WBM sub-base course in normally 10cm compacted thickness.com 32 . softcopy by :.The WBM may be used as a sub-base. free from flaky & elongated particles. the pavement course made of crushed or broken aggregate mechanically interlocked by rolling and the voids filled with screening and binding material with the assistance of water. The screening consists of aggregates of smaller size.Rolling is started from the edges. (v) Application of screening: After the rolling.enough to Transportation Engineering . the roller being run forward and backward until the edges are compacted. to a thickness equal to that of the compacted WBM layer. . generally of the same material as the coarse aggregates. (ii) Provision of lateral confinement: This may be done by constructing the shoulder to advance. compaction is done by three wheeled power roller of capacity 6 – 10 tonnes or alternatively by an equivalent vibratory roller. the dry screenings are applied gradually over the surface to fill interstices in 3 or more application. (iii) Spreading of coarse aggregates: The coarse aggregates are spread uniformly to proper profile to even thickness upon the prepared foundation. c) Binding materials: Binding material consisting of fine grained materials is used in WBM construction to prevent ravelling of stones. Dry rolling is continued to spread screening and brooming is carried out. 2) Materials a) Coarse aggregates: The coarse aggregates used in WBM generally consists of hard varieties of crushed aggregates or broken stones. b) Screenings: The screenings are used to fill up the voids in the compacted layer of coarse aggregates. are cleaned. The foundation layer is prepared to the required grade & camber and dust. . (iv) Rolling: After spreading the coarse aggregates.nissan URL » www. 3) Construction procedure (i) Preparation of foundation for receiving the WBM course: The foundation for receiving new layer of WBM may be either the subgrade or sub-base or base course.wordpress. This is followed by rolling with 6 – 10 tonnes roller. softcopy by :. following are the different types of bituminous pavement construction: (i) Interface treatment (a) Prime coat (b) Tack coat (ii) Bituminous surface dressing (iii) Seal coat (iv) Grouted or penetration type construction (a) Penetration Macadam (b) Built-up spray grout (v) Premix (a) Bituminous bound macadam (b) Carpet (c) Bituminous concrete (d) Sheet asphalt (e) Mastic asphalt (i) Interface treatment The treatment with bituminous material over the existing pavement layer is called interface treatment. the WBM course is allowed to set over-night. (vii) Application of binding materials: After then binding material is applied at a uniform and slow rate at two or more successive thin layer. Construction of Bituminous Pavement Bituminous pavements are in common use in Nepal and abroad. swept and rolled. Additional screening are applied and rolled till coarse aggregates are well bonded and firmly set. the surface is sprinkled with water.No traffic is allowed till the WBM layer sets and dries out. Therefore. On the next day the hungry spots are located and are filled with screening or binding material.After each application.II (vi) Sprinkling and grouting: After the application of screening.Flexible pavement could be strengthened in stages by constructing bituminous pavement layers one after another in a certain period of time unlike the cement concrete pavement construction. It is possible to construct relatively thin bituminous pavement layers over an existing pavement. (viii) Setting and drying: After final compaction. which is necessary to provide the bond between the old and the new layers. . . . the surface is sprinkled with water and wet slurry swept with brooms to fill voids. Types: Based on the method of construction. . lightly sprinkled with water if necessary and rolled. these are commonly adopted as wearing course.notes by Shambhu Kumar Shah enough to Transportation Engineering .com 33 .nissan email: passurexam@yahoo. softcopy by :. (ii) Bituminous surface dressing (BSD) Bituminous surface dressing (BSD) is provided over an existing pavement to serve as thin wearing coat. .The single coat surfacing dressing consists of a single application of bituminous binder material followed by spreading of aggregate cover & rolling.8 kg/10m2 area depending in the type of surface.5 and 10 mm sizes. Function of seal coat to seal the surfacing against the ingress of water.II 2014 a) Prime coat: Bituminous prime coat is the first application of a low viscosity liquid bituminous material over an existing porous or absorbent pavement surface like WBM base course.PC consists of all aggregates passing 20mm & retained on 6. . premixed with bitumen or tar binder are compacted to a thickness of 20 mm to serve as a surface course of the pavement.The seal coat is a very thin layer of surface treatment or a single coat surface dressing. .3mm sieve.Its rate of application is 4. to enliven an existing dry or weathered bituminous surface. (iii) Seal coat Seal coat is usually recommended as a top coat over certain bituminous pavements which are no impervious.The rate of bituminous primer is @ 7. .sentientsep.enough to Transportation Engineering .When the surface dressing is similarly done in two layers.wordpress. (iv) Bituminous premixed carpet Premixed Carpet (PC) consists of coarse aggregates of 12.9–9. . . . b) Tack coat: Bituminous tack coat is the application of bituminous material over an existing pavement surface which is relatively impervious like an existing bituminous surface or a pervious surface like WBM which has already been treated by a prime coat. such as open graded bituminous construction like premixed carpet and grouted macadam. it is called two coat bituminous surface dressing.6 kg per 10m2 area.It is an open graded construction and is covered by a suitable seal coat such as premixed sand-bitumen seal coat before opening to traffic.The main object of priming is to plug in the capillary voids of the porous surface and to bond the loose mineral particles on the existing surface. which is usually applied over an existing black top surface. .com 34 .3 – 14. to develop the skid resistant texture.nissan URL » www. a) Specification of materials: (i) Bitumen: grade ranges between ⁄ and ⁄ . Water absorption 1 % max. (ii) Aggregate: Los Angles abrasion value 35 % max.II (v) Bituminous concrete or Asphalt concrete (AC) Bituminous concrete or Asphalt concrete is a dense graded premixed bituminous mix which is well compacted to form a high quality pavement surface course. density. Impact value 30 % max. Marshall Method is used to fulfil the requirements of stability. uniform spraying of the bituminous binder is done at specified rate. iii) Application of stone chippings: The cover material i.The thickness of bituminous concrete surface course layer usually ranges from 40 to 75 mm.Care should be taken that excessive binder is not applied which may causes bleeding. Construction procedure for surface dressing The bituminous surface dressing (BSD) is done either in a single coat or in two coats over the existing bituminous pavement and for renewal or as a wearing course over a WBM road. softcopy by :. . .A prime coat is applied if the existing base course has a pervious surface like WBM.e. ii) Application of binder: On a prepared surface using a mechanical sprayer. depressions etc.The appropriate temperature for surface dressing is over 160C. .com 35 . Flakiness index 25 % max.Generally.notes by Shambhu Kumar Shah enough to Transportation Engineering . fine aggregates. mineral filler & bitumen and the mix is designed by an appropriate method. . . .nissan email: passurexam@yahoo. are rectified before the treatment is done.The AC consists of a carefully proportioned mixture of coarse aggregates. flexibility and voids. b) Plants and equipment: (i) Bitumen heater (iii) Mechanical blower and hand brushes (ii) Mechanical sprayer (iv) Roller c) Construction Procedure: (1st coat & 2nd coat) i) Preparation of existing surface: The existing surface is prepared to the proper profile and ruts. stone chippings as per the requirement are spread to cover the surface uniformly. . FA and mineral filler coated with bitumen binder and the mix is prepared in a hot-mix plant. v) Application of binder.wordpress. Construction procedure for Bituminous Concrete The bituminous concrete is the highest quality of construction in the group of black to surfaces. 0. stone chipping and rolling for 2nd coat: The process ii).enough to Transportation Engineering .The mixture contains dense grading of CA.sentientsep.com 36 .II 2014 iv) Rolling of 1st or final coat: The rolling is done with a roller of 6–8 tonnes wt.The road section is opened to traffic after 24 hrs.25 mm units 8 to 16 Void in mix 3–5 % Voids filled with bitumen 75–85 % b) Plants and equipment: (i) Hot mix plant (iii) Bitumen distributor (v) Pneumatic roller (ii) Bitumen sprayer (iv) Mechanical finisher c) Construction Procedure: i) Preparation of existing base course: The existing surface is prepared by removing the pot holes or ruts if any. . Flakiness index 25 % max.The irregularities are filled in with premix chippings at least a week before laying surface course. vi) Finishing and opening to traffic: The surface is checked for longitudinal and cross profile using a straight edge of length 3 m and variation in surface greater than 6 mm are corrected. (ii) Aggregates and filler: Los Angles abrasion value 40 % max. . (iii) Bituminous concrete mix: Marshall Stability value. iii) & iv) is repeated again properly for treatment of 2nd coat. This is the final rolling if the surface treatment is in single coat. Impact value 30 % max. after the cover material is spread.Rolling is started from the edges proceeding towards the centre longitudinally with overlapping not less than one third of the roller tread. minimum 340 kg Marshall Flow value.nissan URL » www. . . a) Specification of materials: (i) Binder: Bitumen of grade ⁄ . ⁄ or ⁄ may be chosen depending on climatic condition of locality. softcopy by :.If the 2nd coat is applied then the rolling is done again after the treatment of 2nd coat. nissan email: passurexam@yahoo. Temp.notes by Shambhu Kumar Shah enough to Transportation Engineering . field density test is conducted to check whether it is at least 95% of density is obtained in laboratory. iv) Rolling: The mix after placing on the base course. .Variation in thickness greater than 6mm per 4. .The bitumen may be heated up to 150 – 177 0C and the aggregate temperature should not differ by over 14 0C form the binder temperature.5m length is not allowed. softcopy by :. Rolling can be done by following type of roller: Initial rolling → 8 – 12 tonnes roller Intermediate rolling → 15 – 30 tonnes pneumatic roller Final rolling → 8 – 12 tonnes tandem roller . is thoroughly compacted by rolling at a spread not more than 5 km/hr. a bay or one slab in alternate succession is constructed leaving the next or intermediate bay to follow up after a gap of one week or so.Periodical checks are made for i. Temp. vi) Finished surface: Longitudinal undulation should not exceed 8mm per 300m length & cross profile should not have undulation greater than 4mm.II ii) Application of tack coat: 7. . A tack coat of bitumen is applied @ 6 – iii) Preparation and placing of premix: The premix is prepared in hot mix plant of a required capacity with the desired quality control.The hot mix is carried form mixer to the location and spread by mechanical paver at a temp.For every 100 m2 of compacted surface. Construction Procedure of Plain Concrete Pavement The construction of cement concrete pavement is divided into two groups: (1) Construction of pavement slab (2) Construction of joints 1) Construction Procedure of Cement Concrete Pavement Slab: There are two modes of construction of concrete slab: (i) Alternate bay method: In this method. of mix during mixing & compaction .At least one sample for every 100 tonnes of mix is tested by Marshall Test for above requirements.com 37 .5 kg / 10 m2 area. of aggregate ii. .The wheels of roller are kept damp with water. Aggregate grading iii. of 121 0C – 163 0C. v) Quality control of bituminous concrete construction: Routine checks are carried out at site to ensure quality of mixture & pavement surface. . Grade of bitumen iv. b) Plants and equipment: (i) Concrete mixture (vi) Float (ii) Batching device (vii) Straight edge (iii) Wheel barrow (viii) Belt (iv) Vibrating screed (ix) Fibre brush (v) Internal vibrators (x) Edging tool c) Construction Procedure: i) Preparation of subgrade & sub-base: The subgrade or sub-base should have following requirements: No soft spots are present in the subgrade or sub-base.This technique provides additional working convenience for laying of slab but it has the drawback that large no. softcopy by :. ii) Placing of form works: The form works used may be of steel or wooden. of transverse joints are to be provided. . iii) Batching of material and mixing: Coarse and fine aggregates are measured by weight as per required proportion and cement is measured by number of bags.Construction joints are provided at the end of the day’s job. .The mix should be uniform in colour and homogenous.The mixing of concrete is done in batch mixer which will ensure a uniform distribution of materials throughout the mass.II 2014 . (ii) Continuous bay method: In this method. The subgrade is prepared & checked at least 2 days in advance of concreting. Aggregate (coarse and fine) Proportioning of concrete: .nissan URL » www.Compressive strength 280kg/cm2 at 28 days.enough to Transportation Engineering .wordpress. all the slabs or bays are laid in sequence. . Uniformly compacted subgrade or sub-base extends at least 30cm on either side of concrete width. The forms are jointed neatly and are set with exactness to the required grade and alignment. The subgrade is properly drained. which has the advantage that construction work is running on one half while essential traffic could be diverted on other half end.sentientsep. a) Materials: Cement (OPC).com 38 . notes by Shambhu Kumar Shah enough to Transportation Engineering - II iv) Transporting & placing of concrete: The cement concrete is mixed in quantities such that it can be used within 30 minutes. Care should be taken to see that no segregation is occurred during transportation. - The spreading of concrete is done uniformly. v) Compaction and finishing: The surface of pavement is compacted either by power driven finishing machine or by a vibrating hand screed. The concrete is further compacted by longitudinal float to take out the excessive water. vi) Curing: After 24 hrs. of completion of concrete work, the whole concreting surface is covered with jute mats and the mats are thoroughly saturated with water. - The concreting surface is cured regularly and uniformly for 14 days. vii) Open to traffic: When the concrete attains the required strength or after 28 days of curing the concrete road is opened to the traffic. 2) Construction of Joints There are mainly two types of joints in construction of concrete roads. (i) Longitudinal joints (ii) Transverse joints → (a) Expansion joints (b) Contraction joints (c) Warping joints (d) Construction joints i. Longitudinal joints: Longitudinal joints are provided in cement concrete roads having width over 4.5 m. - Such joints are provided, To allow differential shrinkage & swelling due to rapid changes in subgrade moisture. To prevent longitudinal cracking in concrete pavement. ii. (a) Expansion joints: These joints are provided to allow for expansion of the slab due to rise in slab temperature above the construction temp. of cement concrete. - It is provided at interval of 50 – 60 m. ii. (b) Contraction joints: These joints are provided to permit the contraction of slab. These joints are spaced closer than expansion joints. - The maximum spacing of contraction joint is; Unreinforced slab → 4.5 m Reinforced slab (20 cm thickness) → 14 m. softcopy by :- nissan email:
[email protected] 39 enough to Transportation Engineering - II 2014 ii. (c) Warping joints: Warping joints are provided to relieve stresses included due to warping. ii. (d) Construction joints: It is impossible to construct the whole length of the road in a day, so there is discontinuity in construction at certain section. The joints provided at the end of a day work, is called construction joint. Causes of providing joints in cement concrete pavements: Joints are provided in cement concrete roads for expansion, contraction and warping of the slab due to the variation in the temperature of slab. - Changes of temp. causes expansion of slab horizontally, if there is an increase in slab temperature above the temperature during which the slab was laid. - Similarly, there is contraction of slab also when the temperature falls below the temperature that the slab was laid. - By about mid night the temp. of the bottom slab is higher than the temperature of the slab top, so the slab warps up during this time. Hence, due to above reasons joints are provided in c.c. pavement. Mass Haul Diagram It is a graphical representation of the amount of earthwork involved in road construction and the manner in which may be most economically handled. - Each ordinate in the diagram given below is the balance of materials obtained from cut and used in fill. Haul: In earthwork calculations, the term haul has dual meaning. It is used to describe the distance over which material is moved and also the volumes distance of material used. softcopy by :- nissan URL » www.sentientsep.wordpress.com 40 notes by Shambhu Kumar Shah enough to Transportation Engineering - II Free haul: It is the distance to which the contractor is supposed to move the earth without any additional charge. The charge of free haul is covered by the unit rate of e/w. Overhaul: It is the distance in excess of free haul for which the contractor will be paid extra for each unit of haulages. Economic overhaul: It is a distance to which material from excavation to embankment can be moved more economically than to get material form borrow opening. It can be determined by: a + b.L = (c + a) ⁄ Also, If haul distance be F then, F + L = F + ⁄ Where, a = cost of roadway excavation b = overhaul and tipping in embankment c = cost of borrow pit material L = economical overhaul distance softcopy by :- nissan email:
[email protected] 41 v) Rolling and finishing the paving mix: The rolling is done with 8 – 10 tonnes tandem roller.The rolling is commenced from the edges of the pavement construction towards the centre and uniform overlapping is provided. iv) Placement: The bituminous paving mixture is then immediately placed on the desired location and is spread with rakes to a pre-determined thickness. iii) Premix preparation: The bitumen binder and aggregates are separately heated to the specified temperature of tolerance ±100C and are then placed in the mixer.nissan URL » www. a) Specification of materials: (i) Grade of bitumen: ⁄ . .com 42 .enough to Transportation Engineering . 35 % max. . .The camber profile is checked with a template.The mixing is done till a homogeneous mixture is obtained.II 2014 Construction procedure of Bituminous Bound Macadam road Bituminous bound macadam is a premix laid immediately after mixing and then compacted. softcopy by :. .The roller wheels are kept damp such that the paving mix may not stick to the wheels. . It is suitable only as a base or binder course.Also. . 15 % max.wordpress. (iii) Spreader (iv) Roller c) Construction Procedure: i) Preparation of existing layer: The existing layer is prepared to a proper profile. ⁄ (ii) Aggregates: Los Angles abrasion value Impact value Flakiness index b) Plants and equipment: (i) Sprayer (ii) Mechanical mixer & ⁄ 50 % max. in 300m length. Pot holes are patched and irregularities are made even. number of undulation (>10mm) should be less than 30 nos. ii) Tack coat or prime coat application: A tack coat is applied of thin layer of bitumen binder on the existing black top or WBM layer either using the sprayer or pouring can in proper quantity.A variation greater than 6mm per 3m length is not allowed in the cross profile.sentientsep. The maintenance schedule listed above of routine type and the repairs are carried out at regular interval like day to day and seasonal. (v) Settlement of foundation of embankment of the fill material itself.notes by Shambhu Kumar Shah enough to Transportation Engineering .II 3. 2) Periodic maintenance: It includes renewal of wearing course of pavement surface and preventive maintenance of various items. (iv) Increase in magnitude of wheel loads and the number of load repetitions due to increase in traffic volume. snow fall. arboriculture etc. (ii) Defects in construction method and quality control during construction. Since the highways are exposed to the moving traffic and adverse climatic conditions. Causes of pavement failure: (i) Defects in the quality of materials used. It includes following activities: a) Filling up pot holes and patch repair b) Maintenance of shoulders and cross slope c) Up-keep of road side drains d) Clearing chocked culverts e) Maintenance of miscellaneous items like road signs. frost action etc. high water table. soil erosion.The maintenance operations involve the assessment of road condition.nissan email: passurexam@yahoo. (iii) Inadequate surface or sub-surface drainage in the locality. REPAIR & REHABILITATION Highway Maintenance Highway maintenance is defined as preserving and keeping the serviceable conditions of highway as normal as possible and practicable. .com 43 . whether it is designed and constructed with scientific bias or not. Classification of Maintenance work Highway maintenance work may be broadly classified as: 1) Routine maintenance 3) Special repairs 2) Periodic maintenance 4) Emergency maintenance 1) Routine maintenance: Routine maintenances are needed for any type of road. HIGHWAY MAINTENANCE. they would positively wear out. (vi) Environmental factors including heavy rainfall. diagnosis of problems and adopting the most appropriate maintenance steps. softcopy by :. This is achieved by inspection. man power and equipment. availability of materials. prioritization and planning.nissan URL » www. traffic. softcopy by :. f) Improvement of highway geometrics 4) Emergency maintenance: This maintenance is necessary when any unfavourable conditions occur due to landslides. .The maintenance of these defects may or may not be possible at a time due to limited fund. Prioritisation and Planning of Maintenance Operation After the construction of road.II 2014 3) Special repairs: Special repairs and strengthening of pavements are needed to prevent pavement failure.wordpress. vii) Maintenance cost. Inspection. a lot of defects are found which must be maintained. vi) Availability of funds. Factors to be considered in the maintenance management system: Following factors should be included: i) Minimum acceptable serviceability standards for the maintenance of different categories of roads. So the maintenance of roads should be done according to priorities list without the interference of political parties. the main aim is to get reliable service at minimum possible cost for the whole life. . climate.com 44 .It includes the diversion work temporarily to allow the traffic to pass around the obstructions. v) Type & extent of maintenance requirement and their economic valuation. .sentientsep. ii) Field surveys for the evaluation of maintenance requirements. environmental condition etc. iv) Estimation of rate of deterioration of the pavement under the prevailing set of condition. road wash out due to floods such that the road is closed to pass the traffic. iii) Various factors influencing the maintenance needs such as subgrade soil. drainage.During inspection. It includes: a) Strengthening of pavement structure or overlay construction b) Reconstruction of pavement c) Widening of roads d) Repairs of damages caused by floods e) Providing additional safety measures like islands etc.enough to Transportation Engineering . Wearing course So the stability of pavement structure should be maintained as a whole such that each layer should be stable within itself and thereby make the total pavement maintain its stability. . . 2) Failure in Sub-base or Base course: Following are the main causes of sub-base or base courses failure: ) Inadequate stability or strength ) Loss of binding action ) Loss of base course materials ) Inadequate wearing course ) Use of inferior materials and crushing of base materials ) Lack of lateral confinement for the granular base course 3) Failure in Wearing course: This failure is observed due to following reasons: ) Lack of proper mix design ) Improper gradation of aggregates ) Inadequate binder content ) Inferior type of binder ) Inadequate compaction ) Influence of climate ) Temperature maintain for mixing and placing softcopy by :.II Pavement Failures The pavement failure is defined by the formation of pot holes. 1) Failure in Subgrade: It may be fail due to following two reasons: i) Inadequate stability: It may be due to inherent weakness of the soil itself or excessive moisture or improper compaction. Subgrade b.Stability is the resistance to deformation under stress.The deformation of soil subgrade is found to increase with the increase in number of load repetitions. A.notes by Shambhu Kumar Shah enough to Transportation Engineering . ruts.nissan email: passurexam@yahoo. localised depressions and settlements. Failures in Flexible Pavement The flexible pavement is failed due to the failure of: a.com 45 . Sub-base or base c. ii) Excessive stress application: It may be due to inadequate pavement thickness or loads in excess of design value. cracks.The failure of any one or more components of the pavement structure develops the waves and corrugations on the pavement surface. . enough to Transportation Engineering .This may be caused by the repeated application of heavy wheel loads resulting in fatigue failure.Settlement of fill & sliding of side slopes also would cause this type of failure. . . i) ii) Consolidation or pavement layer: Formation of ruts is mainly due to the consolidation of one or more layers of pavement.This may also be due to moisture variations resulting swelling and shrinkage of subgrade.sentientsep.nissan URL » www. .com 46 . iii) Shear failure and cracking: Shear failures are associated with the inherent weakness of the pavement mixture. .The repeated application of loads along same wheel path cause cumulative deformation resulting in consolidation deformation or longitudinal ruts. softcopy by :. the shearing resistance being low due to inadequate stability or excessive heavy loading. iv) Longitudinal cracking Longitudinal cracking is caused in pavement traversing through the full pavement thickness due to frost action and differential volume changes in subgrade.II 2014 Typical flexible pavement failures: i) Alligator (map) cracking v) Frost heaving ii) Consolidation or pavement vi) Lack of binding (keying) to the lower layer course iii) Shear failure vii) Reflection cracking iv) Longitudinal cracking viii) Formation of waves and corrugation Alligator (map) cracking: This is the most common type of failure and occurs due to relative movement of pavement layer materials.wordpress. Such conditions are occurred in case when bituminous surfacing is provided over the existing cement concrete base course of soil cement base course. .It may result in formation of patches or pot holes.II v) Frost heaving: In the case of frost heaving. . viii) Formation of waves and corrugation: Such type of failure is also common failure and occurs due to poor subgrade condition. improper gradation or mix etc. vi) Lack of binding (keying) to the lower course: Slipping occurs when the surface course is not keyed / bound with the underlying base. vii) Reflection cracking: This type of cracking is observed in bituminous overlays provided over existing cement concrete pavements. defective rolling.The cracks reflected on bituminous surfacing and allow surface water to seep through cracks and cause damage to the soil subgrade. B. . there is mostly a localised heaving-up pavement portion depending upon the ground water and climatic condition.com 47 .nissan iv) Warping cracks v) Mud pumping vi) Structural cracks email:
[email protected] by Shambhu Kumar Shah enough to Transportation Engineering . Failures in Rigid Pavement The failures of rigid pavement are mainly due to following two factors: i) Deficiency of pavement materials: a) Soft aggregates b) Poor workmanship in joint construction c) Poor joint filler and sealer material d) Poor surface finish e) Improper and insufficient curing ii) Structural inadequacy of pavement system: a) Inadequate pavement thickness b) Inadequate subgrade support and poor subgrade soil c) Incorrect spacing of joints Typical rigid pavement failures: i) Scaling of cement concrete ii) Shrinkage cracks iii) Spalling of joints softcopy by :. iii) Spalling of joints: Sometimes when pre-formed filler materials are placed during casting of pavement slabs.Following are the factors which cause mud pumping: i) Extent of slab deflection ii) Type of subgrade soil iii) Amount of free water vi) Structural cracks: Inadequate pavement thickness for the amount and type of vehicles is the prime reason for the structural cracking.sentientsep.The placements of cracks are in longitudinal as well as in transverse direction. this result in development of excessive stresses due to warping and the slab develops cracking at the edges in an irregular pattern. the shrinkage cracks normally develop.com 48 .enough to Transportation Engineering .nissan URL » www. ii) Formation of longitudinal ruts along wheel path of vehicles.This forms an overhang of a concrete layer on the top side. Maintenance of Roads Following maintenance techniques are used for different types of roads: 1. .II i) 2014 Scaling of cement concrete: The scaling is mainly attributed due to the deficiency in the mix or presence of some chemical impurities which damage the mix. joints show excessive cracking and subsidence on later.Due to this defect. ii) Shrinkage cracks: During the curing operation of cement concrete pavements immediately after the construction. iii) Formation of cross ruts along the surface after monsoon due to surface water. .Largely the pavements are found to crack at the corners and edges. Maintenance of Earthen road The damages in earthen roads which may need frequent maintenance are: i) Formation of dust in dry weather. . softcopy by :. the placement is somehow dislocated and filler is thus placed at an angle. iv) Warping cracks: If the joints are not well designed to accommodate the warping of slabs at edges. .wordpress. . v) Mud pumping: Mud pumping is recognised when the soil slurry ejects out through the joints and cracks of cement concrete pavement caused during the downward movement of slab under the heavy wheel loads. . 2.Formation of cross ruts may be due to excessive cross slope.The material so placed in the pot hole. it is necessary to replace the soil binder periodically. .Due to the combined effects of traffic and the rain water. treatment with calcium chloride etc. Corrugations or rutting or shoving develop in such pavement surfaces.notes by Shambhu Kumar Shah enough to Transportation Engineering . ) Pot holes and ruts formed should be patched up. The patch repair work is carried out by first cutting out rectangular shape of defective area to remove the defective materials to the affected depth. ii) Surface treatment: Excess of bitumen in the surface materials bleeds and the pavement becomes patchy and slippery. Following types of maintenance are carried out: ) To prevent the aggregate from getting loosened from surface course.Necessary rolling is done to develop permanent bond between the existing surface and the new materials. Surface treatment c.A premixed material (similar new materials to replacing materials) is then placed in the section.II . is well compacted by ramming having thickness slightly above the general road surface level for future compaction under traffic load.The dust nuisance may be remedied by frequent sprinkling of water. Such ruts should be repaired time to time during and after the monsoon or any type of surface treatment should be provided on the top. Patch repair b. . Resurfacing i) Patch repair: Patch repairs are carried out on the damage or improper road surface by cutting the pot holes to rectangular shape and the affected material in the section is removed until the sound materials are encountered.nissan email: passurexam@yahoo. . Then the same size of fresh aggregates is filled up and compacted well by ramming such that patch area is about 1cm above the general pavement surface. ) Dust nuisance can be effectively prevented by providing bituminous surface dressing course over WBM course. In dry weather dust is formed & during rains mud is formed. . which may not be avoid in untreated earth road in heavy rainfall areas. Generally.com 49 . 3. . Maintenance of WBM roads WBM roads are damaged rapidly due to the heavy mixed traffic & adverse climatic conditions. cut back or emulsion is used as binder.It is customary to spread blotting materials such as aggregates chips of maximum size about 10mm or coarse sand during summer. softcopy by :. stone aggregates are loosened and pot holes and ruts are also formed. Maintenance of Bituminous surface The maintenance works of bituminous surfacing mainly consists of: a. Formation of Wave & Corrugation and Its Remedies: Following are the main causes of formation of wave and corrugation: i) Defective rolling iii) Poor gradation or mix v) Unstable underlying ii) Poor subgrade condition iv) Compaction temp.Kerosene oil is applied on cleaned cracks and the cracks are then filled by suitable grade bituminous sealing compound. . 4.enough to Transportation Engineering . . warping stress etc.wordpress. the joint gap opens and cracks are formed in the old sealer material. Main defect in this type of road is formation of cracks. .nissan URL » www. . if they are well designed and constructed.The dirt.II 2014 iii) Resurfacing: In case the pavement is of inadequate thickness due to increase in traffic load and strengthening is necessary. Maintenance of Cement concrete road It may be noted that very little maintenance such as maintenance of joints only is needed for cement concrete roads. heated to liquid consistency. due to combined wheel load and warping stresses in the slab.sentientsep. which is called resurfacing. subsequently as the slabs contract during winter.Before these cracks get wide enough to permit infiltration of water. dividing the slab length into two or more proximately equal parts due to temperature stress like shrinkage stress.Hence. then an overlay of adequate thickness should be designed and constructed. layer softcopy by :.The maintenance work in such cracks involves first remedy of the basic cause of the failure and then re-casting the failed slab. they should be sealed off to prevent rapid deteriorations. b) Structural Cracks: These cracks are formed near the edge and corner regions of the slab. in between a pair of transverse or longitudinal joints. ) Maintenance of joints: During summer the joint sealer material is squeezed out of the expansion joints due to the expansion of slab. stiff brush and pressure blower.com 50 . . sand and other loose particles at the cracks are thoroughly cleaned using a sharp tool. . ) Treatment of Cracks: The cracks developed in cement concrete (cc) may be classified into two groups: a) Temperature Cracks: These are initially fine cracks or hair cracks formed across the slab. periodic maintenance of the joint sealer is essential both at expansion & contraction joints as a part of routine maintenance work of the cc pavement.The opened-up joints are cleaned with brush and refilled with suitable joint sealer material before the start of rainy seasons. ) Poor subgrade condition: Subgrade consisting of poor soils including highly plastic or organic soils and high water table close to subgrade surface may cause non-uniform and inadequate subgrade stability. All these would contribute to formation of corrugated pavement surface. the solution may be by subgrade treatment using a modifying agent for stabilization. ) Poor gradation or mix: Defective gradation or mix for the surface layer is another factor which gives rise to the wave formation. Pavement Evaluation Pavement evaluation involves a thorough study of various factors such as subgrade support. Usually another layer is laid after laying a levelling course.nissan email: passurexam@yahoo. this would need complete reconstruction. suitable subsurface drainage system is constructed to remedy the defect permanently. the wave formation would continue indefinitely. traffic loading and environmental conditions. If the failure is due to improper compaction of lower layers.notes by Shambhu Kumar Shah enough to Transportation Engineering . ) Compaction temperature: Very high temperature during mixing and compaction (rolling) of bituminous mix would make the resulting pavement surface layers with low stability and wavy surface is formed during rolling. (ii) To investigate structural adequacy of pavement. Remedial Measures: There are no ways to improve the road surface once the waves and corrugations are already formed. (iii) To provide safe and comfortable traffic operations. softcopy by :.com 51 .II ) Defective rolling: If the rolling during construction stage is improper thus leaving the formation of waves then the process being progressive. pavement composition and its thickness. Following are some remedial measures taken for this problem: If the instability of underlying layer is due to excessive moisture conditions. ) Unstable underlying layers: Weak underlying layers also cause the formation of waves due to repeated plying of vehicles on such roads. If the failure is due to subgrade soil which may be highly plastic expansive clay. Objectives: (i) To assess the requirements of pavement so that the maintenance and strengthening job could be planned in time. The present serviceability rating (PSR) is correlated with the physical measurements such as. softcopy by :. . In AASHO road test.nissan URL » www. ) - - Evaluation of pavement surface condition: The surface condition of flexible pavement may be evaluated by the unevenness. patches and cracks. Strengthening of Existing pavements For the successful maintenance of pavements it is essential that they have adequate stability to withstand the design traffic under prevailing climatic and subgrade conditions. profilometer or roughometer and is expressed as unevenness index (cm / km). an overlay would not serve the purpose. The surface condition of rigid pavements may be assessed by the cracks developed and by faulty joints affecting the riding quality of the pavement.II 2014 Approaches and Methods: Following are the various approaches & methods of pavement evaluation: ) Structural evaluation of pavement: The structural evaluation of both flexible and rigid pavement may be carried out by plate bearing test.enough to Transportation Engineering .So in such conditions.If the pavements have to support increased wheel loads and load repetitions.wordpress. .5 cm apart.Field investigations and tests carried out in various countries have shown that the performance of a flexible pavement is closely related to be elastic deflection under loads or its rebound deflection. the solution would be to remove existing pavement and then rebuild the same. ruts. Benkelman Beam is most commonly used.If the existing pavements have completely deteriorated. profilometer was used to record the variable slope angle of the surface formed by two probe wheels spaced 13. . which is called overlay. profilograph.Among various equipment used for this purpose.sentientsep. . the pavements rapidly undergo the distress and no amount of routine and periodic maintenance can help them. as the measurements are easy and simple. degree of cracking and patching etc. the strengthening of existing pavement may be done by providing additional thickness of the pavement of adequate thickness in one or more layers over the existing pavement. . .The structural capacity of the pavement may be assessed by the load carried at a specified deflection of the plate or by the amount of defection at a specified load on the plate. longitudinal and transverse profile of the pavement.com 52 . The pavement unevenness may be measured using unevenness indicator. thus slightly reducing the wheel load stress on the old rigid pavement.nissan email: passurexam@yahoo. Its thickness may be calculated as: hf = 2.II Overlay and its types: The strengthening of existing pavement by providing additional adequate thickness in one or more layers over the existing pavement. b. .com 53 . the wheel load is distributed through a larger area by the overlay. x and n depends upon the pavement and method of overlay construction. the interface between the old and new concrete can’t have perfect bond such that the two slabs could act as a monolithic one. ( ) Its thickness may be calculated as: W here. is called overlay. hf = flexible overlay thickness F = factor depending upon modulus of existing pavement he = existing rigid pavement thickness hd = design thickness of rigid pavement iii) Cement concrete or rigid overlay over rigid pavements: When a rigid or CC overlay is constructed over an existing rigid or cc pavement.Further the maximum temperature differential in the rigid pavement is also decreased due to the bituminous overlay. ho = overlay thickness required (cm) hd = total design thickness required (cm) he = total thickness of existing pavement (cm) ii) Flexible overlay over cement concrete or rigid pavements: A flexible or bituminous overlay when provided over a rigid pavement. It may be of following types: i) Flexible overlay over flexible pavements ii) Flexible overlay over cement concrete or rigid pavements iii) Cement concrete or rigid overlay over rigid pavements i) Flexible overlay over flexible pavements: The overlay thickness required over a flexible pavement may be determined by one of the following method: a) Conventional pavement design method b) Non-destructive testing method (like Benkelman deflection method) The overlay thickness required as per conventional method is given by: ho = hd + he Where. ho = rigid overlay thickness hd = design thickness he = existing pavement thickness Values of a.notes by Shambhu Kumar Shah enough to Transportation Engineering .5 (F × hd – he) Where. thus causing a substantial reduction in the warping stress and also in the maximum combined stress. softcopy by :. according to width of pavement. Procedure: The stretch of road length to be evaluated is first surveyed to assess the general condition of the pavement w.6 – 0.Larger rebound deflection indicates weaker pavement structure which may require earlier strengthening or higher overlay thickness.The CBR method of pavement design as recommended by the IRC is adopted for finding the total design thickness of the flexible pavement for the design traffic volume. cracks and undulations.) may be taken on each of the selected stretch.A minimum of 10 deflection observations (preferably 20 nos.com 54 . . The overlay thickness required is given by: ho = hd – he overlay = ho existing = he hd Fig: Overlay Design (ii) Overlay design by Benkelman Beam deflection method: Benkelman Beam is a device which can be conveniently used to measure the rebound deflection of a pavement due to dual wheel load assembly or the design wheel load.sentientsep. the ruts. . . fair & poor and length of each stretch should not be less than 500m.The stretches are classified and grouped into different classes such as good.The loading points on the pavement are located along wheel path on a line 0.t. there is an elastic recovery or rebound defection of the deformed pavement surface. .nissan URL » www.r. .The existing thickness of the pavement is found from test pits dug along the wheel path on the pavement. .enough to Transportation Engineering . .wordpress.9 m from the pavement edge.The amount of pavement deflection is a measure of the structural stability of the pavement system. Principle: A well compacted pavement section or one which has been well conditioned by traffic deforms elastically under each wheel load application such that when the load moves away. This is the basic principle of deflection method. softcopy by :.II 2014 Design of Overlay It may be designed by one of the following methods: i) Conventional design method ii) Non-destructive testing method (like Benkelman beam deflection method) (i) Conventional Design method: The total pavement thickness requirement is designed for the design traffic and the existing conditions of subgrade. 5 And.Df) + 2k (Di – Df) . and also the tyre pressure is checked.5 Where. The rebound deflection value D at any point is given by. if Di – Df > 2. Overlay thickness design: Overlay thickness design (ho) can be determined as. iv) Similarly. Similarly for next deflection point. between front and rear leg.7m from the point and a further distance of 9. between bearing of the beam & rear adjusting leg e = dist. iii) The initial dial gauge reading Do is noted. ii) The probe end of the Benkelman beam is inserted between the gaps of the dual wheel and is placed exactly over the observation point. d = dist. D = 2 (Do . above process is repeated. vi) The temperatures of pavement surface are recorded at interval of 1 hr. R Da Dc ̅ σ = deflection reduction factor (= 10 ~ 15) = allowable deflection (= 0. between dial gauge & rear adjusting leg f = dist.0m respectively. if Di – Df ≤ 2.enough to Transportation Engineering . D = 2 (Do – Df) .II notes by Shambhu Kumar Shah .75 ~ 1. following procedure is done: i) The truck is driven slowly parallel to the edge and stopped such that the left side rear wheel is centrally placed over the first point for deflection measurement. 1) For bituminous overlay: (cm) Where. intermediate gauge reading Di and final gauge reading Df is taken at a distance of 2. when the rate of change of pavement deflection is < 0.25 mm) ̅ = +σ = characteristic deflection = =√ mm (̅ (= mean deflection value) ) (= standard deviation) 2) For granular or WBM overlay: (mm) softcopy by :.nissan email:
[email protected] mm / minute.com 55 .After marking the deflection observation points. Di and Df form a set of readings at one deflection point. v) The three deflection dial reading Do. 0 mm 1. 1.45 Solution: ̅ √ (̅ ) ̅ Deflection after temperature correction = 1.5%. of yrs. 1.99 mm Assume. 1. 1. 5. no.25 cm # softcopy by :. 1. 1. if the pavement temperature during the test was 390C and the correction factor for subsequent increase in subgrade moisture content is 1.40.5 × ½ = 8.45. allowable deflection (Da) = 1.65.32. 1. The deflection values obtained in mm after making the necessary lag corrections are given below. 1.5 mm Where.531 * 1.6 kg/cm2 pressure.25 mm 1.com 56 . Design traffic. (n) = 2 A = P [1 + r] (n+10) = 750 [1 + 0. Adopt IRC guidance. 1. 1.50. 1.enough to Transportation Engineering .sentientsep.35.nissan URL » www. Assume an equivalency factor of 2.3 = 1.531 mm Corrected deflection for subgrade moisture = 1.25. determine the thickness of bituminous overlay required.52. Value of Da 1.0065 = 1. vehicles / day ( A is between 1500 – 4500) Overlay thickness of granular material.wordpress.36. 1.46.3. 2014 Projected design traffic (A) 1500 – 4500 450 – 1500 150 – 450 A = P [ 1 + r ] (n + 10) Numerical Benkelman Beam deflection studies were carried out on 15 selected points on a stretch of flexible pavement during summer season using a dual wheel load of 4085 kg. Thickness of bituminous overlay = 16.55.075] (2 + 10) So. Assume annual rate of growth of traffic as 7. If the present traffic consists of 750 commercial vehicles /day.60. 1. 1.0 mm = 1786 com. 1.II Da is given by.0 for bituminous overlay.48.4.557 – (39 – 35) × 0. .com 57 . Following are the various factors which affect human (road user) characteristics: i) Physical Characteristics: The physical characteristics of road users may be either permanent or temporary. .Permanent characteristics are the vision. tools. strength and the general reaction to traffic situations.notes by Shambhu Kumar Shah enough to Transportation Engineering .The various studies to be carried out on the actual traffic include speed. . convenient and economic movement of people and goods. TRAFFIC ENGINEERING Intro Traffic engineering is that branch of engineering which deals with the improvement of traffic performance of road networks and terminals. signals and islands are most common means to regulate and control the traffic. .Temporary characteristics are fatigue. Impact of Human and Vehicular characteristics on traffic engineering: 1) Human Characteristics: The human element is involved in all actions of the road users either as pedestrian. etc. sight distance.The planning is separate phase for major highways like express-ways. capacity. car driver or motorist.II 4. techniques and findings for safe. parking. cross section. . cyclist. Following are the main scope of traffic engineering: a) Traffic characteristics d) Planning and analysis b) Traffic studies and analysis e) Geometric design c) Traffic operation. rapid. accident studies. with least number of traffic accidents. all fall under the scope of traffic engineering. . volume.Improvement of road geometries like horizontal and vertical alignment. travel pattern.All these reduce alertness and increase the reaction time and also affect the quality of judgement. arterial roads and parking facilities.nissan email: passurexam@yahoo. . Scope of Traffic Engineering The basic object of traffic engineering is to achieve efficient. alcohol or drugs and illness. . destination.Traffic engineering deals with the application of scientific principles. origin. free and rapid flow of traffic. hearing.Study of traffic characteristics is the most essential prerequisite for any improvement of traffic facilities.Installation of traffic control devices like signs. control & regulation f) Administration and management . softcopy by :. . over taking distance. weight an maximum turning angle.The traffic stream may consist of mixed traffic or heavy traffic whereas the facilities to overtake faster vehicles may be limited. . iv) Environmental Characteristics: The various environmental factors such as fog. acceleration and braking characteristics.nissan URL » www.com 58 . .The speed and acceleration depends upon the power of the engine and the resistance to be overcome and are important in all the geometric design elements. at valley curves. affect the behaviour of road user. rules of roads and traffic regulation. . driving practice. . heavy sunlight.sentientsep. turning on sharp curves etc. because it is possible to design a road for a particular vehicle having standard dimension & weight but not for an indefinite vehicle.enough to Transportation Engineering . skill. The following vehicular characteristics affecting road design may be classified as: i) Static Characteristics: Static characteristics of vehicles affecting road design are the dimensions. . iii) Psychological Factors: The emotional factors such as attentiveness.The length of vehicle affects the capacity. psychology of road users will be quite useful for safe traffic operation.Knowledge of vehicle characteristics. rain.wordpress. superstition impatience. facilities to the traffic. . heat. softcopy by :. ii) Dynamic Characteristics: Dynamic characteristics of vehicles affecting road design are speed.The facilities to the traffic may be location of fuel station. . fear. parking. general attitude towards traffic regulation and maturity also come under this. anger. . maintenance workshop etc.The environmental conditions affecting the behaviour of road user are traffic stream characteristics.II 2014 ii) Mental Characteristics: Knowledge. intelligence.The deceleration & braking characteristics guide safe vehicle operation. . etc.The height of driver seat affects the visibility distance. 2) Vehicular Characteristics: It is quite important to study the various vehicular characteristics which affect the design & traffic performance. traffic behaviour.The height of vehicle affects the clearance of the overhead structures.The height of head light affects the head light sight dist. experience and literacy can affect the road user characteristics. atmospheric conditions and the locality. The regulations should be rational. recording and disposing traffic violation cases.com 59 . it is essential to impose adequate traffic regulation and traffic control devices.The general requirement of traffic control devices are: attention. meaning. driver and all other road users. TRAFFIC CONTROL DEVICES The various aids and devices used to control. ii) Vehicle controls: These include vehicle registration. pedestrian controls etc. time for response and respect of road users.notes by Shambhu Kumar Shah enough to Transportation Engineering .6m away from the edge of the kerb. Traffic regulations and laws cover the following four phases: i) Driver controls: These include driving licences for light and heavy motor vehicles. . Types of traffic signs are: (a) Regulatory or mandatory signs (b) Warning or cautionary signs (c) Informatory signs softcopy by :. fitness and inspection of vehicles. The signs should be placed such that they could be seen and recognised by the road users in time. speed limit. . financial responsibility & civil liability. requirements of vehicles. turning and overtaking etc. driver tests & minimum requirements. Traffic regulations: The traffic regulations should cover all aspects of control of vehicles. regulate and guide traffic may be called traffic control devices. equipment and accessories. prohibition signs.nissan email:
[email protected] edge of the sign adjacent to the road is not less than 0.II Traffic operation and regulations: In order to have safe traffic operations on roads. weight. maximum dimensions. Following are the most common traffic control devices: (1) Traffic signs (3) Markings (2) Traffic signals (4) Islands (1) Traffic signs The traffic sings are mounted on sign posts. iii) Flow regulations: Regulations of traffic flow have been laid down such as directions. It also includes regulatory signs like one way. iv) General controls: Some other general regulations and provisions are made to report accidents. No parking sign is meant to prohibit parking of vehicles at that place.way signs iv) Restriction end signs ii) Prohibitory signs v) Direction control signs iii) No parking / stopping signs vi) Speed limit signs . .The stop sign is intended to stop the vehicles on a roadway and the giveway sign is used to control the vehicles on a road so as to assign right of way to traffic. (b) Warning: Warning or cautionary signs are used to warn the road users of certain hazardous conditions that exist on or adjacent to the roadway. .enough to Transportation Engineering . safe and pleasant. the appropriate directions in which the vehicles are obliged to proceed. These are further classified as: i) Stop and give.com 60 . regulations and prohibitions.nissan URL » www.Speed limit signs are meant to restrict the speed of all or certain classes of vehicles on a particular stretch of a road.II 2014 (a) Regulatory signs: These signs are used to inform the road users of certain laws. These are divided into: Direction and place identification signs Parking signs Facility information signs softcopy by :.wordpress. . provide information to make travel easier. inform them of destination and distance. use of horns or entry of certain vehicle class. (c) Informatory Signs: These signs are used to guide the road users along routes.sentientsep. .They have a white back ground.The warning signs are in the shape of equilateral triangle with its apex pointing upwards. red border and black symbols.Direction control signs indicate by arrows. .Prohibitory signs are meant to prohibit certain traffic movements. . They provide all the vehicles to move approximately at same reasonable speed along the major road traffic. .The red light is meant for ‘stop’. Types of Traffic signals: The signals are classified as follows: i) Traffic Control Signals: The traffic control signals have three coloured light glows facing each direction of traffic flow. provide meaning and time to respond with the minimum waste of time. Pedestrians can cross the roads safely at the signalised intersections. They reduce the accidents.com 61 . Advantages of traffic signals: They provide orderly movement of traffic and increase the traffic handling capacity at intersections. softcopy by :. the green light indicates ‘go’ and the amber or yellow light allows the ‘clearance time’.nissan email: passurexam@yahoo. Failure of the signal due to electric power or any other defect may cause confusion to the road users. Automatic traffic signal may work out to be economical compound to manual control. .enough to Transportation Engineering . Disadvantages: The rear-end collisions may increase.II notes by Shambhu Kumar Shah (2) Traffic signals Traffic signals are control devices which could alternately direct the traffic to stop and proceed at intersections using red and green traffic light signals automatically.The main requirements of traffic signal are to draw attention. Improper design and location of signals may lead to violations of the control system. Longitudinal solid lines are used as guiding or regulating lines and are not meant to be crossed by the driver. . . ii) Pedestrian Operated Signals: These signals are meant to give right of way to pedestrians to cross a road during walk period when vehicular traffic shall be stopped by red.Yellow colour markings are used to indicate parking restrictions.enough to Transportation Engineering . symbols by using paints in contrast with colour and brightness of the pavement. warn.Also the markings on kerb with alternate black and white line increase the visibility from long distance. culvert head walls etc. ii) Kerb Markings: These may indicate certain regulations like parking regulations. kerb. b) Manually operated signals: are those which are operated manually. level crossing gates.These obstructions may be supports for bridge. guide or regulate the traffic.Transverse solid lines indicate the position of stop lines for vehicles. a cycle of red. . . iv) Reflector Unit Markings: Reflector markers are used as hazard markers (yellow light) and guide markers for safe driving during night.com 62 . words.wordpress. patterns. sides of island etc. softcopy by :. c) Traffic actuated (automatic) signals: are those in which the timing of the phase & cycle are changed automatically according to traffic demand. . narrow bridges. These may be classified as: i) Pavement markings v) Road delineators ii) Kerb markings a) Roadway indicators iii) Object markings b) Hazard marker iv) Reflector unit markings c) Object marker i) Pavement Markings: Pavement markings may generally be white paint. . iii) Object Markings: Physical obstruction on or near the roadway are hazardous and hence should be properly marked. amber & green lights.These are made of lines. iii) Specific Traffic Signals: (3) Road Markings Road or traffic marking may be called special signs intended to control.sentientsep.nissan URL » www.II 2014 a) Fixed-time signals: are those in which the timings of the phase & cycle are set to repeat regularly. (iii)Pedestrian loading islands: These are provided at regular bus stops and similar places for the protection of passengers. Numericals A vehicle was stopped in 1. (ii) Channelizing islands: These are used to guide the traffic into proper channel through the intersection area.enough to Transportation Engineering .These are useful when the direction of flow is to be changed. . . .These can reduce the possible conflicts between traffic streams. particularly when the area is large. Solution: We have.com u = – at 63 . email: passurexam@yahoo. Determine the average skid resistance. (ii) v2 – u2 = 2as or. Following are the types of traffic islands based on the function: (i) Divisional islands (iii) Pedestrian loading islands (ii) Channelizing islands (iv) Rotary islands (i) Divisional islands: Divisional islands are intended to separate opposing flow of traffic on a highway with four or more lanes.II notes by Shambhu Kumar Shah (4) Traffic Islands Traffic islands are raised area constructed within the roadway to establish physical channels through which the vehicular traffic may be guided. . (iv) Rotary islands: Rotary island is the large central island of a rotary intersection and is much larger than the central island of channelized intersection. (i) v = u + at.It eliminates the head on collisions and also reduces the accidents.nissan v = o. 0 – a2t2 = 2as softcopy by :.4 sec by fully jamming the brakes and the skid marks measured 7 m.These are very useful as traffic control devices for intersection at grade. Based on approach volume.8 – 0. 18m wide road B.36 = 19.36 sec # Red time.2 sec Hence.36 sec GA (new) GB (new) = 23. Green time. Road A. GA = (tB + It) – AA Road B.36 + 3 = 23.2 + 4 + 19 + 3 = 49. An isolated signal with pedestrians’ indication is to be installed on a right angled intersection with road A.2 + 0.II 2014 Given. The heaviest volume per hour for each lane of road A & B are 275 and 225 respectively.8 × GB (adjust) = 0.8 sec GA (adjust) = 0.2) = 0. AA = 4 sec Amber time for road B. AB = 3 sec Initial interval to start crossing = 7 sec (= It ) Now. for A & B respectively. (t) = 1. The approach speeds are 55 and 40 kmph. RA RB softcopy by :. adopt cycle length (c) = 50 sec Adjusting the additional period of (50 – 49.wordpress. Design the timings of traffic and pedestrian signals.44 = 0.nissan = = GB + A B = GA + AA URL = 19.64 sec = 19 + 0. Solution: Assume. Green time is calculated as. L = (s) = 7 m Braking time.com # # 64 . 12m wide. GB = (tA + It) – AB = (10 + 7) – 4 = (15 + 7) – 3 = 13 sec = 19 sec Now. Total cycle length = GA+ AA + GB + AB = 23.36 sec = 27.2 m/s Amber time for road A.64 sec » www. # = 22.44 = 23.enough to Transportation Engineering . Pedestrian walking speed = 1.sentientsep. Braking distance.44 sec.64 + 4 = 0.4 sec. Sa Sb = 1250 PCU/hr.4 sec ≈ 67.com # 65 .25 Now. n = 2 = no. Y = ya + yb = 0. Solution: Normal flow. DWA = RB = 27.25 = 0.64 sec DWB = RA = 22.5 sec email:
[email protected] sec ≈ 29 sec Ga = ( ) = (67. respectively.9 Gb = ( ) = (67.64 sec # # The average normal flow of traffic on cross roads A and B during design period are 400 and 250 PCU/hr.nissan = 12 sec = 2 sec. All-red time (R) Assume. Design two phase traffic signal by Webster method. = 1000 PCU/hr. L = 2n + R = 2 × 2 + 12 = 16 sec where.57 Total lost time per cycle.5 – 16) = 22.36 sec WB = C – (RA +tB) = 50 – (22. for each road = GA + GB + R + AA + AB = 29 + 22.II notes by Shambhu Kumar Shah Design of pedestrian signal: Do not walk (DW) period. (co) = = = 67. Amber time (A) Total cycle time softcopy by :. Ratio.. Saturation flow. of phase R = 12 sec = red time required Now. the saturation flow values on these roads are estimated as 1250 and 100 PCU/hr.32 + 0.32 yb = = = 0. WA = C – (RB + tA) = 50 – (27.5 – 16) = 28. Optimum signal cycle. The all-red time required for pedestrian crossing is 12 sec.5 + 12 + 2 + 2 = 67. qa qb = 400 PCU/hr.36 sec # # For walk (w) period. = 250 PCU/hr.enough to Transportation Engineering .5 sec Here. ya = = = 0.64 + 15) = 7.36 + 10) = 17. II softcopy by :.com 2014 66 .nissan URL » www.wordpress.enough to Transportation Engineering .sentientsep. b) This study is used in planning.com 67 . The various traffic studies carried out are: 1) Traffic volume study 4) Traffic flow characteristics 2) Speed studies 5) Parking study i) Spot speed study 6) Accident study ii) Speed and delay study 7) Traffic capacity study 3) Origin and Destination (O & P) study 1) Traffic volume study: Traffic volume is the number of vehicles crossing a section of road per unit time at any selected period. magnetic detectors and radar detectors. b) Manual Counts: This method employs a field team to record traffic volume on the prescribed record sheets. .notes by Shambhu Kumar Shah enough to Transportation Engineering . traffic operation and control or existing and new facilities.Other methods of working the mechanical detectors are by photoelectric cells. . cross walks.Traffic volume is used as a quantity measure of flow. TRAFFIC STUDIES Intro Traffic studies or surveys are carried out to analyse the traffic characteristics.Traffic count is recorded by electrically operated counters and recorders capable of recording the impulses. geometric design and computing roadway capacity. d) Useful in structural design of pavement. signal timing.The commonly used units are vehicles/day and vehicles/hour. c) This study is used in the analysis of traffic pattern and trends.nissan email: passurexam@yahoo. . softcopy by :. . Following are the objects and uses of traffic volume studies: a) To measure the relative importance of roads and in deciding the priority for improvement and expansion. channelization etc Counting of traffic volume: Traffic volume counts may be done by following ways: a) Mechanical Counters: The mechanical counters can automatically record the total number of vehicles crossing a section of the road in a desired period. These studies help in deciding the geometric design feature and traffic control for safe and efficient traffic movements.II 5. e) Used for planning sidewalks. such as vehicle classification. time. .The arithmetic mean is taken as the average speed. d) To study the traffic capacity and decide the speed trends. it is possible to obtain data which can’t be collected by mechanical counters.wordpress. Overall speed or travel speed is the effective speed with which a vehicle traverses a particular route between two terminals. Presentation of Spot speed data (a) Average speed of vehicles: From the spot speed data of the selected samples. environment and driver.II 2014 . There are two types of speed studies carried out: i) Spot speed study: Following are the uses of spot speed study: a) To use in planning traffic control and in traffic regulations. frequency distribution tables are prepared by arranging the data in groups covering various speed ranges & the number of vehicles in such range. at a specified section or location. c) To use in accident studies.The drivers exceeding 85th percentile speed are usually considered to drive faster than the safe speed under existing conditions and hence this speed is adopted for the safe speed limit at this zone.enough to Transportation Engineering .nissan URL » www. Measurement of spot speed: (i) By finding running speed of vehicles over a short distance of < 50 m.sentientsep. (ii) By finding instantaneous speed while crossing a section. . 2) Speed studies: The actual speed of vehicles over a particular route may fluctuate widely depending on several factors such as geometric features.This method is very commonly adopted due to the specific advantages over other methods. place. . softcopy by :. Running speed is the average speed maintained by a vehicle over a particular stretch of road.By this method. Spot speed is instantaneous speed of veh. (b) Cumulative speed of vehicles: A graph is plotted with the average values of each speed group on the x-axis and the cumulative percentage of vehicles travelled at or below the different speeds on the y-axis. traffic conditions. while the vehicle is in motion. Travel time is the reciprocal of speed. b) To use in geometric design – for redesigning existing highway.com 68 . Average speed is the average of the spot speeds of all vehicles passing a given point on the highway. turning movements and counts. duration frequency and causes of the delay in the traffic stream.This curve will have a definite peak value of travel speed across the section and this speed is denoted as modal speed. .The 15th percentile speed represents the lower speed limit. softcopy by :. . . ii) Speed and delay study: The speed and delay studies give the running speeds. location.notes by Shambhu Kumar Shah - enough to Transportation Engineering . b) plan the schedule of different modes of transportation for the trip demand of commuters. . There are various methods of carrying out speed and delay study: (a) Floating car or riding check method (d) Elevated observations (b) License plate or vehicle number method (e) Photographic technique (c) Interview technique 3) Origin and destination (o & d) studies: The origin and destination (o & d) study is carried out mainly to a) plan the road network and other facilities for vehicular traffic. . The efficiency of the roadway is judged form the travel time.II 98th percentile speed is taken for the purpose of highway geometric design.The delay or the time lost by traffic during the travel period may be either due to fixed delays or operational delays.They also give the information such as the amount. . (c) Modal Average: A frequency distribution curve of spot speeds is plotted with speed of vehicles or average values of each speed group of vehicles on the x-axis and the % of vehicles on the y-axis. fluctuations in speeds and the delay between two stations of a road spaced far apart.The studies are utilised in finding the travel time and in benefit-cost analysis.nissan email: passurexam@yahoo. overall speeds.com 69 .This graph is called the speed distribution curve. as the data is collected quickly in short duration.II 2014 .These studies are most essential in planning new highway facilities and in improving some of the existing systems. route. by a group of persons and the answers to prescribed questionnaire are collected on the spot.This method is quite easy and quick as far as field work is concerned.sentientsep. ii) Licence plate method: The entire area under study is cordoned out and the observers are simultaneously stationed at all points of entry and exit on all the routes leading to and out of the area. . To locate intermediate stops of public transport.com 70 . . . Applications of O & D studies: To judge the adequacy of existing routes and to use in planning new network of roads. purpose of trip.enough to Transportation Engineering . To locate expressway or major routes along the desire lines.The method however involves a lot of office computation in tracing the trips through a network of stations. softcopy by :. . . . type of vehicle and number of passenger in each vehicle. To locate new bridges as per traffic demands.wordpress.nissan URL » www. To locate terminals and to plan terminal facilities. .The observers at all points note the license plate number (registration number) of the vehicles entering and leaving the cordoned area and the time. their origin and destination in each zone under study.O & D study gives information like the actual direction of travel.The information collected is time of origin & destination. Methods of collecting O & D data: Following are the methods for collecting the O & D data: i) Road side interview method iv) Tag-on-car method ii) Licence plate method v) Home interview method iii) Return post cart method i) Road side interview method: The vehicles are stopped at previously decided interview stations. and there is delay to vehicular movement.This method is simple and quick. selection of routes and length of the trip. To plan transportation system and mass transit facilities.The O & D studies of vehicular traffic determine their number. .The main drawback of the method is that the vehicles are stopped for interview. Weaving: Waving is the combination of diverging and merging. Following are the main aspects which are studied during parking studies: (i) Parking demand (ii) Parking characteristics (iii) Parking space inventory (i) Parking demand: The parking demand may be evaluated by different methods.In industrial. as shown in fig: Diverging: Diverging is the process of leaving the lane by the vehicle and gaining either left or right of the existing lane. Merging: Merging is the process of mixing the vehicle form left or right of main lane.com 71 .Also it can be done by noting the registration number of each parked vehicle at any desired time interval (such as 30 minutes. . the action is termed as weaving.The basic traffic manoeuvres are diverging.Diverging on left is easiest movement causing least problem of traffic conflicts. commercial and residential places with multi-storeyed building.II notes by Shambhu Kumar Shah 4) Traffic flow characteristics: Traffic stream has flow and counter flow along a common route. . 5) Parking study: Parking is one of the most important places in transportation system. parking demand is particularly high. One of the methods is by making cordon counts of the selected area and recording accumulation of vehicles during the peak hours by subtracting the outgoing traffic from the traffic volume entering the cordoned area. . . at relatively and small angle of crossing.nissan email: passurexam@yahoo. . unless the stream is separated into pair of one-way flows by proper design or regulation. demanded by automobile users especially in big cities.When a vehicle moves obliquely across the path of another vehicle moving in the same direction. Crossing: Crossing is the process of passing a lane perpendicular to other lane.enough to Transportation Engineering . merging and crossing. softcopy by :. 1 hour etc.). . . pedestrians etc. personal injuries or even casualties. Types of parking facilities: (a) On-street parking: - - When the parking facility is provided on kerb. 450. 6) Accident study: Accident in traffic engineering is defined as a phenomenon which may occur with the combination of vehicular traffic. . (b) Off-street parking: - When the parking facility is provided at a separate place away from the kerb.It is also necessary to study parking pattern.nissan URL » www. The main advantage of this method is that there is no undue congestion and delay on the road as in kerb parking. interference to smooth flow or traffic and accidents involved during parking and unparking.wordpress.enough to Transportation Engineering . The maximum vehicles that can be parked.com 72 . . Objectives: The following are the main objectives of the accident studies: i) To study the causes of accidents ii) To suggest corrective treatment at potential location. Parallel parking Angle parking accommodates more vehicles per unit length of kerb. 600 or 900 b. (iii) Paring space inventory: The area under study is fully surveyed and a map is prepared showing all places of parking facilities to meet the parking demand.II 2014 (ii) Parking characteristics: The study is directed to note the present parking practices prevalent in the area and general problems in parking. The chance of accidents in angle parking is more. Angle parking : 300. On-street parking is further divided into: a. presence of mixed traffic and pedestrians. But the main drawback is some of the owners will have to walk a greater distance after parking the vehicles.It is occurring due to complex flow patterns of vehicular traffic.sentientsep. Parallel parking is generally preferred when the widths of kerb for parking space as well as width of the street are limited.The traffic engineer has to strike a balance between capacity and parking demand and to design proper facilities for parking. 450 parking is considered the best one.Traffic accidents may involve property damages. is with an angle of 90 o. it is known as off-street parking. softcopy by :. it is on-street parking. 7) Traffic capacity study: Following related terms are often used in traffic capacity study: (i) Traffic volume (iii) Traffic capacity (v) Possible capacity (ii) Traffic density (iv) Basic capacity (vi) Practical capacity (i) Traffic volume: Traffic volume is the number of vehicles moving in a specified direction on a given lane or roadway that pass a given point or cross section during specified unit of time. carelessness in using the carriageway. improper lighting and improper traffic control devices. tyre burst or any other defect in vehicles. steering system. temporary effects due to fatigue.com 73 . Causes of accidents: Following are the causes of accidents: (i) Road users (a) Drivers (b) Pedestrians (c) Passengers (ii) Vehicle defects (iii) Road (a) Road condition (b) Road design (iv) Environmental factors (v) Other factors Drivers: Excessive speed and rash driving. Pedestrians: Violating regulations. snow. alcohol etc. fall under the causes of accidents due to drivers. semi-naked girl etc. fog. dust. carelessness. inadequate width of shoulders. .enough to Transportation Engineering . sign or signal. v) To make computation of financial losses. softcopy by :. violation of rules and regulation.nissan email:
[email protected] is expressed as vehicles/hour or vehicles/day. Passengers: Alighting from or getting into moving vehicles. sleep. Environmental factors: Unfavourable weather condition like mist. iv) To support proposed design. improper curve design. badly located advertisement boards or service stations. Road design: Defective geometric design like inadequate sight distance. smoke or heavy rainfall which restrict normal visibility and render driving unsafe. pot holes. ruts and other damaged conditions of the road surface. Vehicle defects: Failure of brakes. Other factors: Stay animals on the road. lighting system. incorrect sign and signals. Road condition: Slippery or skidding road surface.II notes by Shambhu Kumar Shah iii) To evaluate the existing design. no knowledge about traffic rules and regulation etc. length of vehicle or. S = 0.Traffic volume is the product of traffic density and traffic speed.e.The average spacing (s) between c/c of vehicles is equal to the average length of vehicles plus the clear spacing between the vehicles in the stream.II 2014 (ii) Traffic density: Traffic density is the number of vehicles occupying a unit length of lane of roadway at a given instant.7 sec) softcopy by :.com 74 .nissan URL » www. . Determination of theoretical maximum capacity: An estimate of theoretical maximum or basic capacity of a single lane may be made from the relation: (i) Here. V = avg. . . S = Sg + L Where.sentientsep.278 V * 0.It is expressed as vehicles/km. without traffic density being so great as to unreasonable delay. . m . S = 0. . hazard or restriction to the driver’s freedom to manoeuvre under the prevailing roadway and traffic conditions. kmph S = avg. vehicles/hour V = speed.It is the theoretical capacity.enough to Transportation Engineering . C = capacity of a single lane. (v) Possible capacity: Possible capacity is the maximum number of vehicles that can pass a given point on a lane or roadway during one hour under prevailing roadway and traffic condition. (vi) Practical capacity: Practical capacity is the maximum number of vehicle that can pass a given point on a lane or roadway during one hour./lane. speed in m/s & kmph resp.2 V + L (ii) t = reaction time (taken as 0.278 V t + L L = avg. (iv) Basic capacity: Basic capacity is the maximum number of passenger cars that can pass a given point on a lane or roadway during one hour under the most nearly ideal roadway and traffic conditions. i. vehicles/hr. (iii) Traffic capacity: Traffic capacity is the ability of a roadway to accommodate traffic volume. i. S = 0. c/c spacing of vehicles OR space headway.e.It is expressed as the maximum number of vehicles in a lane or a roadway that can pass a given point in unit time.7 + L v. =vt+L Sg = minimum space gap in m or.The basic capacity depends upon the speed (v) and spacing (s).wordpress. ) are converted to one common standard vehicle unit. i. vehicles/hour (3600 sec) Ht = minimum time headway in second Passenger Car Unit (PCU) It is quite difficult to estimate the traffic volume and capacity of roadway facilities under mixed traffic flow. traffic control devices etc. acceleration and braking characteristics. Factors affecting practical capacity: Following are some important factors that affect the practical capacity: i) Lane width: As the lane width decreases. unless the different vehicles classes (such as cars. . time headway decreases and after reaching a minimum value at an optimum speed. .Thus in mixed traffic flow. it is a common practice to consider the passenger car as the standard vehicle unit to convert the other vehicle classes and this unit is called passenger car unit (PCU). ii) Lateral clearance: Vertical obstructions such as retaining wall or parked vehicles near the traffic lane reduce the effective width of lane and thus reduction in the capacity of lane. pedal cycles. buses. we get the theoretical capacity of traffic lane with homogeneous traffic flow. rural or urban roads. or PCU/lane/hr. power. trucks. the maximum theoretical capacity of a traffic lane may be obtained.Hence. Factors affecting PCU values: Vehicles characteristics such as dimensions.85m from the pavement edge to the obstruction is considered desirable so that capacity is not affected adversely. softcopy by :. .II By putting the value of ‘S’ from eqn (ii) to the eqn (i). bullock carts etc. starts increasing. the practical capacity of a traffic lane also decreases.com 75 . Transverse and longitudinal gaps or clearances between moving vehicles. one way traffic.Hence. Roadway characteristics such as road geometrics including gradient.notes by Shambhu Kumar Shah enough to Transportation Engineering . if the minimum time headway (Ht) is taken. motorcycles.nissan email: passurexam@yahoo. the traffic volume and capacity are expressed as PCU/hr. and traffic density as PCU/km length of lane. Where. Regulation and control of traffic such as speed limit.e. curve etc.. vans.A minimum clearance of 1. Environmental and climatic conditions. . speed. It has been observed that the increase in speed of traffic stream. C = capacity. presence of intersections etc. . thus reducing capacity. Presentation of Traffic volume data: i) Annual Average Daily Traffic (AADT): AADT is the total volume of vehicle traffic of a particular highway or road for a year divided by 365 days. resulting in a great reduction in the capacity of lane.nissan URL » www. vehicular and driver characteristics. . softcopy by :. weekly or hourly as per requirement.sentientsep.It is also useful for analysing the rate of traffic accidents on a roadway. .II 2014 iii) Width of shoulder: Narrow shoulders reduce the effective width of traffic lanes as the vehicles travel towards the centre of the pavement. one or two way traffic movement. vi) Presence of intersection at grade: Intersections restrict free flow of traffic and thus adversely affect the capacity of lane.com 76 . .enough to Transportation Engineering . design facilities and economic considerations. iv) Commercial vehicles: Large commercial vehicles like truck and buses occupy greater space and also heavy commercial vehicles may travel at lower speeds especially on grades which may affect the other traffic in the same lane.One of the most important uses of AADT is for determining funding for the maintenance and improvement of highway.e.wordpress.AADT is useful for the measurement of busyness of the road.The 30th highest volume is hourly volume which is generally taken for design purposes in both view point i. It is usually the 30th highest hourly volume for the design year. the capacity will decrease. vii) Other factors: The other factors that affect the capacity of lane are number of traffic lane. iii) Thirtieth (30th) Highest Hourly Volume: It is also known as Design Hourly Volume (DHV). generally taken 20 yrs. . from the time of construction completion.Its measurement may be seasonal. ii) Average Daily Traffic (ADT): It is the volume of traffic counted on the roadway over a given time period (greater than 1 day but less than 1 year) divided by the number of days in that period. . v) Alignment: If the alignment and geometrics are no up to the design standards.Average daily traffic also estimates to monitor the growth in traffic on a roadway and for funding of major improvement. 41 3. cumulative speed distribution curve is plotted.00 2.53 11.06 3.47 24.enough to Transportation Engineering . of vehicles observed 255 119 43 33 9 Determine: (i) Upper & lower values of speed limits for regulation of mixed traffic.00 76.41 12 18 68 89 204 255 119 43 33 9 850 total cumulative freq. kmph → softcopy by :. kmph 0 to 10 10 to 20 20 to 30 30 to 40 40 to 50 No. kmph mid speed.00 5. % 1. of vehicles observed 12 18 68 89 204 Speed range.00 10.II notes by Shambhu Kumar Shah Numerical s Spot studies were carried out at a certain stretch of a highway and the consolidated data collected are given below: Speed range.00 95.12 8.53 22.nissan email:
[email protected] 98.88 1. kmph frequency 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 5 15 25 35 45 55 65 75 85 95 frequency % = 1.00 46. cumulative frequency % → 100 98 % 90 85 % 80 70 60 50 40 30 20 15 % 10 0 0 10 20 30 40 50 60 70 80 90 100 mid speed. Solution: Frequency distribution of spot speed data: speed range.00 14.94 100.06 100 Using the values of mid speed and cumulative frequency % column.00 90.00 30. (ii) The design speed for checking geometric design elements of highway. kmph 50 to 60 60 to 70 70 to 80 80 to 90 90 to 100 No.com 77 . √ √ √ √ softcopy by :. collide with each other.sentientsep.4 & 6 tonnes.com 78 .55. Original speed of vehicles before application of brakes are obtained. A from west and B from south. vehicle A skids in a direction 500 north of west and vehicle B 600 east of north. The initial skid distances of the vehicles A & B are 38 and 20 m respectively before collision. √ √ √ √ Speeds of vehicles just before collision.nissan URL » www. If the weight of vehicles A & B are 4. The average skid resistance of the pavement is found to be 0.enough to Transportation Engineering .wordpress. After the collision. The skid distances after collision are 15 and 36 m respectively.II i) Upper speed limit for regulation = 85th percentile speed = 60 kmph # ii) Lower speed limit for regulation = 15th percentile speed = 30 kmph # iii) Speed to check design elements = 98th percentile speed = 82 kmph # 2014 Two vehicles A & B approaching at right angles. Solution: Speeds of vehicles just after collision. calculate the original speeds of the vehicles. iii) Adequate visibility should be available for vehicles approaching intersection. ROAD INTERSECTIONS Intro General area of road or street about which two or more roads join or cross including the roadway and roadside facilities for traffic movement within it. crossing and weaving are called intersections at grade. the area of conflict should be as small as possible. Basic requirements of intersections i) At the intersection. ii) The relative speed and particularly the angle of approach of vehicle should be small. by a traffic lane or more.II 6. v) Geometric features like turning radius and width of pavement should be adequately provided.When the pavement is widened at the intersection area. diverging. vii) Good lighting at night time is desirable. . unless controlled by traffic signals or police. is called road intersections. it is known as flared intersection. vi) Proper signs should be provided on the road. viii) If the number of pedestrians and cyclist are large. softcopy by :. Types of Intersections: i) Intersections at grades a) Un-channelized intersections b) Channelized intersections c) Rotary intersections ii) Grade separated intersections a) Over-pass intersections b) Under-pass intersections 1) Intersections at grades: All road intersections which meet at about the same level allowing traffic manoeuvres like merging. easiest in design. separate provision should be made for the safe passage in intersections. iv) Sudden change of path should be avoided.notes by Shambhu Kumar Shah enough to Transportation Engineering .nissan email: passurexam@yahoo. a) Un-channelized intersections: The un-channelized (all paved) intersections are the lowest class of intersection.com 79 . it is called plain intersection.When no additional pavement width for turning movement is provided. . but most complex in traffic operations resulting in maximum conflict area and more number of accidents. c) Rotary intersections: A rotary intersection or traffic rotary is an enlarged road intersection where all converging vehicles are forced to move round a large central island in one direction (clockwise) before they can weave out of traffic flow into their respective directions radiating from the central island. to control their speed and angle of approach and to decrease the conflict area at the intersection. Speed control can be established over vehicles entering the intersection.enough to Transportation Engineering . The channelizing islands provide proper place for installation of design and other traffic control devices. softcopy by :. thus reducing the total conflict area available in the unchannelized intersection.nissan URL » www.com 80 . . Points of conflicts can be separated. which help to channelized turning traffic.sentientsep. .The main objects of providing rotary intersection are to eliminate the necessity of stopping even for crossing streams of vehicles and to reduce the area of conflict.II 2014 b) Channelized intersections: Channelized intersection is achieved by introducing islands into the intersectional area. Angle between intersecting streams of traffic may be kept as desired in a favourable way.The islands of proper shape and size are designed. Both the major and minor conflict area within the intersection can considerably be decreased. Advantages of channelized intersections: Vehicles can be confined to definite paths.wordpress. nissan email: passurexam@yahoo. Total cost may be very high where space is limited & costly built up areas. There is no necessity of traffic police or signal to control the traffic. Limitations These require comparatively large area of land. These are advantageous when the number of intersecting roads is between 4 and 7. The capacity of rotary intersection is the highest (i. The possible number of accidents & severity of accidents are quite low. Hence the journey is more consistent and confortable when compared with any other intersection at grade. In places where there is mixed traffic and large number of cyclists and pedestrians. the operation and control of traffic become complex. 3000 vehicles/hour) than other intersections. It is the simplest traffic controlled intersection and its maintenance cost is almost nil. All traffic including those turning right or going straight across the rotary have equal opportunity as those turning left. The variable cost of operation of automobile is less at a traffic rotary than at a signalized intersection.notes by Shambhu Kumar Shah enough to Transportation Engineering . These are unsuitable in the intersecting roads having more than 7. softcopy by :.II Elements of Rotary Intersections: Advantages and Disadvantages of Traffic Rotary: Advantages Crossing manoeuvre is converted into weaving or merging and diverging operations.e.com 81 . wordpress.This type of intersection causes least delay and hazard to the intersections at grade from the point of view of traffic safety and efficient operation. Design of Intersections At the intersection there are through. rotary become troublesome. merge or cross. which should be minimum. When distance between intersections is less. the relative speed will also be low.It depends on the absolute speed of intersecting vehicles and the angle between them. its construction can’t be justified. .enough to Transportation Engineering . 2) Grade separated intersections Grade separated intersection design is the highest form of intersection treatment.The point where the possible path of two vehicles intersect is called conflict points and the area containing conflict points is called conflict area. . . (ii) Manoeuvre areas: Manoeuvre areas are those areas where there is a potential collision. When the traffic volume is low.When the angle of merging is small. Following factors are to be considered in intersection design: (i) Relative speed (ii) Manoeuvre areas a) Elemental manoeuvre areas b) Multiple manoeuvre areas (i) Relative speed: Relative speed is the vector difference in the velocities of two vehicles in the same flow and is the sum of the speeds of approaching vehicles from opposite direction.sentientsep. .Elemental manoeuvre areas are those formed by only two single oneway lanes of flows when they diverge. . turning and crossing traffic and these traffic movements may be handled in different ways depending upon the type of intersection and its design.II 2014 These are also unsuitable where the angle of intersection of two roads is too acute.Multiple manoeuvre areas are those formed by two one-lane one-way flows are present. softcopy by :.As the relative speed increases. .nissan URL » www. channels of approach and departure is influenced. . the judgement of drivers regarding time and distance is likely to be more inaccurate and the possibility and severity of accident will increase.com 82 . These are the simplest manoeuvres. Traffic operations are much more complex and hence are to be avoided in the intersection design. where there is limited right of way like built up or urban area.nissan email: passurexam@yahoo. There is overall increase in comfort and convenience to the motorists and saving in travel time. it is called over-pass. Disadvantages It is very costly to provide complete grade separation & interchange facilities.Separation of intersection roads by means of a bridge thus eliminating all crossing conflicts at the intersections. grade separation may introduce undesirable crests and sags in vertical alignment. It is possible to adopt grade separation for all likely angles.notes by Shambhu Kumar Shah enough to Transportation Engineering .A highway grade separation is achieved by means of vertical level. Advantages and Disadvantages of Grade Separation Advantages: It provides maximum facility to cross the traffic and avoids accidents while crossing.com 83 . Factors to be considered in traffic rotary Following are various design factors to be considered in traffic rotary: i) Design speed viii) Channelizing islands ii) Shape of central islands ix) Camber and super elevation iii) Radius of rotary roadway x) Sight distance and grade iv) Weaving angle & weaving distance xi) Lighting v) Width of carriageway xii) Traffic signs vi) Entrance and exit curves xiii) Provision for cyclists & pedestrians vii) Capacity of the rotary softcopy by :. . There is increased safety for turning traffic.The grade separation may be either by an over-bridge or under-bridge. Grade separation is an essential part of controlled access highway. Construction of grade separation is costly. In flat or plain terrain. b) Under-pass When the highway is taken by depressing its profile below the general GL to cross another road by means of an under-bridge.II . even right turn movement is made quite easy. it is known as under-pass. . difficult and undesirable. a) Over-pass When the major highway is taken by raising its profile above the general ground level by embankment and an over-bridge across another highway. nissan URL » www.sentientsep.com 2014 84 .wordpress.II softcopy by :.enough to Transportation Engineering . It is economical to use the largest lamp size in a luminaire which will provide sufficient uniformity of pavement brightness. Factors influencing night visibility Following factors affect the night visibility of the object: i) Amount and distribution of light flux from the lamps ii) Size of the object iii) Brightness of the object iv) Brightness of the background v) Reflecting characteristics of the pavement surface vi) Glare on the eyes of the driver vii) Time available to seen an object Design factors of Highway Lighting Various factors to be considered in the design of road lighting are: i. When the brightness of object is less than that of background. discernment is by reverse silhouette.) Spacing of lighting units vi. On urban roads where the density of population is also high. projections above the pavement surface such as island or vehicles may be seen by this process of reverse silhouette. its type.nissan email: passurexam@yahoo. TRAFFIC LIGHTS - Importance of Road Lighting One of the various causes of increased accident rate during night may be attributed to poor night visibility. Highway lighting is particularly more important at intersections. size and colour depends on several considerations in addition to distribution of light flux. i.When the brightness of the object is more than that of the immediate background. discernment is principally by silhouette. like feeling of security and protection. i) softcopy by :. but road lighting may be considered as an added facility to the road users. If brightness of pavement is uniformly increased. The various lamps used are filament.) Luminaire distribution of light v.) Lighting layouts Lamps The colour of the lamp. fluorescent etc. when object appears darker than road surface.) Height & overhang of mounting ii.) Lamps iv.II 7.com 85 .) Lateral placement iii. level crossings and in places where there is restriction of traffic to movements. bridge site. road lighting has other advantages.e. The objects adjacent to the roadway. . discernment by silhouette is enhanced.notes by Shambhu Kumar Shah enough to Transportation Engineering . Head lights of vehicles may be sufficient for safe night driving. free movement of traffic is obstructed. the utilisation coefficient charts are available for determination of average lux of intensity over the roadway surface where lamp lumen. softcopy by :. width of pared area and spacing of lighting poles are known. higher values being preferred where possible. single side lighting is sufficient but for two way lane or wider roads.sentientsep. it is necessary to have proper distribution of light. vi) Lighting layouts The lighting layout may be of single side. shadow and the glare effect from street lamps depend also on the mounting height. The distribution should be downward so that high percentage of lamp light is utilised for illuminating the pavement and adjacent area. The illumination is necessary for traffic sigh and objects. If they are too close to the carriageway. Special care should be taken while locating the lights on curves. iii) Spacing of light units The spacing of lighting units is often influenced by the electrical distribution poles. The lights are located on outside of the curves to provide better visibility. Usual mounting heights range from 6m to 10m. property lines. v) Lateral placement Street lighting poles should not be installed close to the pavement edge.enough to Transportation Engineering . iv) Height and overhang of mounting The distribution of light. staggered (both sides) or central. road layout and type of side features & their illumination. For single lane or narrow roads. Design of Highway Lighting System For various types of luminaire distribution. decreasing the capacity of roadway. The minimum vertical clearance required for electric power lines up to 650 volts has been specified as 6m above pavement surface (as per IRC). mounting height.wordpress.com 86 .nissan URL » www. Lights are installed at closer spacing on curves than on straights. Large lamps with high mountings and wide spacing should be preferred from economy point of view. staggered lighting should be installed.II 2014 ii) Luminaire distribution of light To have the best utility of the luminaire or source of light. lux = 6.II notes by Shambhu Kumar Shah 0. Solution: The ratio. Numerical Design a street lighting system for the following conditions: Street width : 15 m Mounting height : 7. From the chart 5.com 87 .4 0.6 street side 0. Coefficient of utilization = 0.8 email:
[email protected] Assume maintenance factor = 80 % softcopy by :.3 0.5 m Lamp size : 6000 lumen Luminaire type : II Calculate the spacing between lighting units to produce avg.2 house side 0.1 0 0 1 2 3 4 5 6 Ratio.enough to Transportation Engineering .5 0.nissan = 0. Fig: Coefficient of utilisation The following relationship is used for computation of spacing: - The maintenance factor is taken as 80 %.7 Coefficient of utilization 0.46 (page 256). com 2014 88 .nissan URL » www.enough to Transportation Engineering .wordpress.II softcopy by :.sentientsep. ix) Bridge should be economical in terms of construction and maintenance. telephones etc. iv) Suitable high banks above high flood level on each side.notes by Shambhu Kumar Shah enough to Transportation Engineering . vii) Absence of expensive river training works. According to the span (NRS 2027): (i) Minor Bridge (span < 20 m but total length is < 20 m) (ii) Medium Bridge (span < 20 m but total length is > 20 m) (iii) Major Bridge (span > 20 m) softcopy by :. . v) Foundation should be kept on firm ground and they should be kept at sufficient depth to avoid damage by floods. vi) Bridge should fit into surrounding landscape.com 89 . x) Economical approaches which should not be very high or long or liable to flank attacks of the river during flood. ix) Proximity to a direct alignment of the road to be connected. vi) Absence of sharp curves in approaches. Characteristics of an Ideal Bridge: i) The line of bridge should not have serious deviation from the line of approach road.nissan email: passurexam@yahoo. iii) The width of bridge should be sufficient to cater future traffic. viii) Bridge surface should be similar to road surface.II 8. v) Rock or other hard erodible strata close to the river bed level.According to NRS 2027 the cross drainage structure whose span length is more than 6m is called bridge and less than 6m is called culvert. iv) Bridge should carry standard loading with reasonable factor of safety. viii) Avoidance of expensive ground water construction. Classification of Bridges A. BRIDGE AND TUNNELING BRIDGE A structure constructed over an obstacle to provide the passage is known as Bridge. ii) Steady river flow without serious whirl and cross currents. Choice of Location of Bridge Site The characteristics of location of bridge site are as follows: i) A straight reach of the river. iii) A narrow channel with firm banks. ii) It should be in level. vii) Bridge should provide passage for services like water pipe. guard stones etc. According to loading (NRS 2027): (i) Major Bridge (HS 20 – 44 or IRC class AA or any other equivalent loading or class 70R additional loading) (ii) Medium or Minor Bridge (HS 15 – 44 or IRC class A or any other equivalent loading) (iii) Temporary bridge (HS 15 – 44 or IRC class B or any other equivalent loading or class 70R additional loading) C. parapet walls. C = 4.com 90 . Decking consisting of girders or trusses or cables and slab.enough to Transportation Engineering .5 H Where. Length of Clear Span: i.wordpress. Hydraulic Analysis of Bridge 1. From Lacey’s formula. Linear Waterway: i. Approaches to bridge to connect the road or railway to the bridge proper. River training works like revetment for slopes for embankment at abutment and aprons for bed necessary at upstream & downstream side.nissan URL » www. v. iv. W = C√ . For masonry arch bridge: ii. Foundation for the abutments and piers or towers. Linear Waterway. ii. According to the Structure: (i) RCC T-bridge or RCC simply supported bridge (ii) Cantilever bridge (single or double) (iii) Arch bridge (iv) Suspended or suspension bridge (v) Stayed cable bridge (vi) Steel bridge (vii) Movable bridge D. deck slab etc. Linear waterway is width of stream for one edge to another. for large alluvial deposit Where. vii.sentientsep. S=2H S = clear span H = height of abutment on pier including foundation 2. ii.5 softcopy by :.II 2014 B. vi. For RCC bridge: S = 1.5 ~ 6. trusses. According to the Materials: (i) Timber Bridge (iv) Steel Bridge (ii) RCC Bridge (v) Floating Bridge (pantron bridge or boat bridge) (iii) Masonry Bridge Components of a Bridge The components of bridge are classified into two groups: a) Substructure: portion below the bearings b) Superstructure: portion above the bearings Following are the different component parts of the bridge: i. Bearing for the girder. Handrails. Abutment and piers or towers. iii. roads and vehicles through mountain and underground water bodies. Q = C A ii.com 91 . Purposes ) To provide passage ways for rail. Design Discharge: ⅔ i. ) To relief the congestion on surface road. under the water bodies or through mountains.5 Note: When a bridge is constructed across a contracted stream. N = number of span 4. water on the upstream will rise up.nissan email: passurexam@yahoo. 5. Number of Spans: i. If w < span length (s). Afflux: * Where. ) To avoid the long routes around the mountain.5 ~ 6. According to Purpose D. According to Supporting Arrangement (ii) Free flowing tunnels (i) Tunnel supported by shot Crete (ii) Tunnel supported by RSJ section C. ii. If w > span length (s). ) To carry water for power generation. According to Shape (i) Traffic tunnels (i) Circular (ii) Conveyance tunnels (ii) D-shaped (iii) Mining tunnels (iii) Semi-elliptical (iv) Horse-shoe B.II notes by Shambhu Kumar Shah 3. According to Pressure (i) Pressure tunnels E. single span bridge. From empirical relationship. From area velocity method. + x = afflux in meter L = width of stream v = velocity of normal flow c = 4. w = N S Where. Types of Tunnels: The tunnels can be classified on following basis: A. ) To provide access for water supply. According to Lining (iii) Tunnel supported by shotcret & RSJ section (i) Lined tunnels (iv) Tunnel supported by RCC (ii) Unlined tunnels softcopy by :. Q = A V TUNNEL A tunnel is an underground structure beneath the ground.enough to Transportation Engineering . This rise in water level near the bridge site is called afflux. waste water collector etc. iii) Semi-elliptical section: This section is more stable. These sections are structurally strong to withstand external rock and water pressures. Survey of Tunnel Alignment While selecting the alignment following points should be considered: i) Shortest iii) Easily available ii) Straight iv) Careful selection of Entry & Exit location softcopy by :. circular section is considered the best. compacted metamorphic rocks where external pressure due to rock & water are not very large.nissan URL » www. it is difficult for excavation. hard.II Component parts of tunnel Following are the components of tunnel: (1) Rib beam (2) Rock bolting (3) Shotcrete 2014 (4) Lining Tunnel cross-sections Following cross sections are generally used: i) Circular section iv) Horse shoe section ii) D-shaped section v) Rectangular or square section iii) Semi-elliptical section i) Circular section: The circular section is most suitable for structural considerations.In a case where the tunnel is subjected to high internal pressure but does not have good quality or rock. .wordpress. As the shape of the arch nearly coincides with the line of pressure. iv) Horse shoe section: These sections are compromise between circular and D-shaped section.sentientsep.com 92 . However. ii) D-shaped section: This section is suitable for tunnels located in good quality in fact sedimentary rocks & massive external igneous. particularly where the cross section area is small.enough to Transportation Engineering . the arch section can be made relatively thinner keeping stress within allowable limits. Attempts made in seal off the rock by grouting with cement. . v) To bring down the temperature raised by diesel engines. v) The electric circuit of the lighting should be divided into a number of independent circuits with their isolators and fuse boxes separate.nissan email: passurexam@yahoo. The problem may be due to surface as well as subsoil water. Object of Ventilation Following are the main objective of ventilation: i) To replace the used air by fresh air in tunnel. softcopy by :. The drainage arrangements for keeping off and removing off water may be classified into three systems: i) Pre-drainage ii) Dewatering of tunnel or drainage during construction iii) Permanent drainage iv) Incandescent lamps should be fixed in the centre of the roof of the tunnel. iv) To remove the excessive moisture. it is not always possible to follow a straight alignment because of the following parameters affecting the design of tunnels: (i) Topography (ii) Geological section along the alignment (iii) Ground and/or rock water loads along the alignment (iv) Rock mechanics properties (v) Creep or tectonic movement along the tunnel (vi) Other parameters: a) Rock temperature b) Presence of methane gas c) Geometric design Tunnel Drainage Since the tunnel is constructed below the original ground level. chemical or concrete linings.notes by Shambhu Kumar Shah enough to Transportation Engineering . Ventilation of Tunnels The process of removing used or vitiated air by fresh air from tunnel is called ventilation.com 93 . therefore tunnel have drainage problem.II However. vi) Provision of flood lights should be made at suitable interval for detailed inspection for the particular length of spot. ii) To remove harmful obnoxious gases and dust for safe working space. iii) To supply oxygen for workers in the tunnels. enough to Transportation Engineering - II 2014 Methods of Ventilation Ventilation can be done by following two methods: ) Natural Method: This method is normally applicable in short tunnels. The natural draft can be depended to renew the air inside the tunnel. - In straight reaches where uniform grade exists, tunnel up to 100m length would need not any artificial ventilation. ) Artificial Method: In this method, artificial measures are done to control moisture, dust and temperature in the tunnel. It is also known as mechanical ventilations. Following are the three artificial method of ventilation: a. Blowing in fresh air b. Exhausting foul air by ducts c. Combination of blowing in and exhaust system Lining of Tunnels Tunnel lining is a part of support design. It can take form of shotcrete lining, concrete lining or steel lining. Following are some of the methods used for tunnel lining: i) Unsupported rock v) Segmental system ii) Rock reinforcement lining vi) Monolithic concrete iii) Shotcrete lining vii) Precast pipe segments iv) Steel ribs Objectives: i) To reduce the losses in system. ii) To protect steel ribs from deterioration. iii) To protect the turbine form loose rock particle falling into the water. iv) To take part of internal pressure induced by water. Method of Tunnelling: The choice of a particular method depends upon the nature of the strata and the geometry of the tunnel section. It may broadly be divided in following categories: 1. Tunnelling in firm ground i) Traditional methods a) Full face method b) Top beading and benching method c) Drift method ii) Excavation by tunnelling method 2. Tunnelling in soft ground 3. Tunnelling in rock softcopy by :- nissan URL » www.sentientsep.wordpress.com 94 notes by Shambhu Kumar Shah enough to Transportation Engineering - II 1. Tunnelling in firm ground: The methods to be adopted depend upon the shape, size of available equipment. The methods adopted fall under the following categories: i) Traditional methods: (Drilling and Blasting) Depending upon the type of strata, size of tunnel and method adopted; excavation is supported by temporary wooden supports or permanent steel supports. Different methods under this category are: a) Full face method: This method is suitable for comparatively firm soils where the excavated portion can hold itself for sufficient time to permit mucking and supporting operations to be completed. - The method is recommended for tunnel or small size. - Excavation is done in three section i.e. top, middle & bottom. b) Top beading and benching method: The beading is excavated and supported to the full length or part length of the tunnel before benching is started. - The heading is always ahead of the benching by a convenient length and may be formed by excavation the full width of the tunnel above the springing line. c) Drift method: In the case of large tunnels a pilot tunnel or drift is made in the side or at the centre of the tunnel. - The drift is then widened by drilling holes on its face as shown in figure. ii) Excavation by tunnelling method: This method is suitable for large tunnel in soft soil. - In this method excavation is done and support is also arranged simultaneously. 2. Tunnelling in soft ground: In case of soft soil requiring instantaneous support; drilling and blasting is not done. - In this method the board driven ahead to support the ground ahead of the last rib are known as spiles. - The fore poles act as cantilevers beyond breasting and carry the weight of the ground till the steel rib supports their forward ends. softcopy by :- nissan email:
[email protected] 95 enough to Transportation Engineering - II 2014 - The soil should be excavated out after removing the breast boards and the new rib is created in position. 3. Tunnelling in rock: Tunnels are driven in rock by repeating in sequence the operation of drilling hole in the rock face, loading the holes, with explosive, blasting, removing and disposing off the broken rock. The following are commonly adopted method of tunnelling in rock: i) Full face method ii) Top heading and benching method iii) Drift method - - - - - Hydraulic Analysis of River: The hydraulic analysis is required for new locations, proposed facility replacements and widening of existing facilities. So, flood frequency for design and checks must be considered for new location, replacement or modification of facility. The intent of design flood is to establish conditions under which the highway facility will provide uninterrupted service with minimal damage to the highway. The design flood must not overtop the highway. A check flood must be applied on proposed highway or stream crossing facilities to determine whether a proposed crossing will cause significant damage to the highway or to any other property. Analysis should include a comparison of existing conditions for interim and estimated future watershed characteristics. Occasionally, flood control system may have been constructed that significantly reduce runoff rates at the highway site. Hydraulic analysis is required not only for the selection of proper stable and durable site conditions to implement the proposed facilities (i.e. highway, bridge etc.) replacement and widening of existing facilities but also for the replacement or relocation of any kind, bridge superstructure replacement if the hydraulic opening of the bridge is changed in anyway, channel modifications including the placement of bank stabilization material, scouring action of bridge foundation by high current of flood, fill placed in flood plain, excavation in flood plain, overtopping of bridge due to HFL etc. Occasionally abridge or culvert will be inundated by backwater from a downstream river. Hence, in this case hydraulic analysis is conducted to control tail water. Hydraulic analysis is required to provide channel restoration plan which help the avoidance of barriers for fish/aquatic movement, maintain or improve water quality, recreation, aesthetics and flow capacity. softcopy by :- nissan URL » www.sentientsep.wordpress.com 96 sentientsep.notes by Shambhu Kumar Shah enough to Transportation Engineering .wordpress.nissan email:
[email protected] The End Thank You Wishing you all the very best! For more updates Visit: www.com 97 .com softcopy by :.