IRC 8 1-1997GUIDELINES FOR STRENGTHENING OF FLEXIBLE ROAD PAVEMENTS USING BENKELMAN BEAM DEFLECTION TECHNIQUE (First Revision) INDIAN ROADS CONGRESS 1997 << IRC:81~i997 GUIDELINES FOR STRENGTHENING OF FLEXIBLE ROAD PAVEMENTS USING BENKELMAN BEAM DEFLECTION TECHNIQUE (First Revision) Published by THE INDJAN ROADS CONGRESS Jamnagar House, Shahjahan Road, New Dethi4lOOll 1997 Pnce Rs. 120/.. lP~us Packing & Postage) << IRC:8 11997 First published : November, 1981 Reprinted: March, 1991 First Revision : July, 1997 .Repr~nted Octoher~20(Xi) (with amendntents (Rights ofPublication and of iran,’~Lnon arc reserved) Printed at Dee Kay Printers, New i)elhi (500 copies) << Mb.CPWD. S-487. Tawartnalani I)r. Kadiyali & Associates. CS. Dhir RN. 4. Ministry of Surface Transport (Roads Wing). Ml’.C.). New Delhi Engineer-in-Chief. PWI).. NEW DELHI AddI. CR. Narain. ER. 96) 1. Al). E-23. Qtrs.A-1/133. Safdarjang Enclave. of India. P. CSIR (Retd. Garg Dr. Public health Engg. MOST (i) << . New Delhi-I 10048 * ADC(R) being not in position. Dr. New Delhi-I 10029 Chief Engineer (Mcch. Lucknow-22&X)1 Engineer-in-Chief. Shanna (Member-Secretary) CC. Gandhinagar-382fl10 Synthetic Asphalts. Roorkee Secretary to the Govt. Narain* (Convenor) S. 103. R & H Depu.). Govt. 3. Environment & Forests (Retd. Sachivalaya Complex.). New l)elhi-l 10011 Professor & Coordinator. the meeting was presided by Shri AD. Narayanan II.IRC:81-1997 MEMBERS OF THE HIGHWAYS SPECIFICATIONS AND STANDARDS COMMITTEE (As on 313. Kadiyali Chief Consultant. DG(RD). 9. 5. town Hall. Chembur. New Delhi Chief Engineer (R) Stds/R. Bangalore-560009 6. Bombay-400074 Chief Engineer (CCC). Ministry of Surface Transport (Roads Wing). Jayawant KS. Martin Marg. 10. lInd Floor.14. New Delhi-I 10021 Chief Engineer (Nil. H. Central Govt. Gupta 8. of Gujaral.. Greater Kailash-1. Block No. Agarwal Maj. ER. St. AK.P.. Dr. University of Roorkee. Nirman Bhawan. Centre ci iransport Engg. 2. DirectorCeneral ~S&P). Matik DC (RD).. Delhi-I 1(X)(Ws Director. 12.). 7. Municipal Corporation of Delhi. Ananda Rao Circle. UP. Jamdar MB.. Pooja Mahul Road. Ministry of Surface Transport (Roads Wing).1). Ramesh 13. LI. New Dellii-l 10003 Director. Singh 24... Saxena 23. Prof. New Delhi-I 10049 Transport Engg. College. 9. Ltd. ofCivil Engg. Indian Roads Construction Corpn.. VinodKumar 18.. Bahadurshah Jafar Marg.E. Justo (ii) << . MOST (Retd). 20. Delhi-Mathura Road.J.T. 27. New Delhi-I 10018 National Council for Cement & Building Materials. Deptt. Artrnachal Pradesh. South Extn. Madrar-600025 Chief Engineer (Civil). Ceotechnical Engg. hanagar-791 Ill Director. 6. New Delhi Prof. I)elhi-Mathura Road. Rao 19.CRRI. 21.K.Scn 26. New E)elhi Chief Engineer (Plsnnning). Ring Road. HauzKhas. New Delhi-I 10016 ‘Badr’i’.. National Institute for Training of Highway Engineers. NinanKoshi The Director General. RAT Mehta R. 28.G. Prof. P. Rao Prof. Ministry of Surface Transport (Roads Wing). Civil. 22.L. Faculty of Engg. Okhla. Manak Bhawan. DC(RD). Minion of Surface ‘Iransport (Roads Wing).Core. Scope Complex. Swaminathan B. DV. Bangalore University. Bureau of Indian Standards. of Civil Engg. S. 56. Dr. R. Regional Engg. Nalanda Apartment. 17. 6th floor. 15.O. Section. Megu M. Bangalore 16. Raghava Chad.t.New Delhi Chief Engineer fI’&T). (IV. Jor Bagh. of Civil Engg. Koul Prof.A. Madras -600028 Chief Engineer (Zone-I). C. C. Central Road Research Institute. Lodhi Rosd. Thinivankadam Street. Guindy. Purans. Division. 25. Central Road Research Institute. 174. The Director A.). New Delhi-I h(XX)2 Dy. Warangal Director & Head (Civil Engg.G. New Delhi-I 10020 Prof. P-21. New Delhi-I 10020 Highway Research Station. PWD. 50. I. Vikaspuri.IRC:8 1-1997 14. P. l)irector & lhead. G. AK. Srivastava 34. Engineers & Management Associates. Guram. Faridahad MS. OP. Indian Roads Congress Ex-Officio 38. 36. Deptt. New Delhi. Narendra Singh R. LI-in-Chief’s Branch. Kashmir Ilouse. Punjab PWD. Delhi-I 10092 13-190. Director General/DS Dte. Jam President. Noida-201301 (iii) << . Block-B. N. lihatia R. 32./R Ministry of Surface Transport (Roads Wing). New Delhi-I 10001 D.IRC:81 -1997 29. Kashmir House. CT. Sharma - 33.S. Lc. Ranganathan 118164. of Transport Planning. Treasurer. Chad Prof.N. H. Indian Roads Congress DG(RD) & lion.K. institutional Area.. Army Hqrs. Patiala A. Core-8. Dy. Narain S. Sector-16A. 7. DIIQ P0. Kakateeya Apartments. 2nd Floor. New Delhi-I 10011 Director (Technical).New Dclhi-110003 ChiefConsultant. Plot 86. 31. General Border Roads.W. Vasant Kunj. Oil Coordination Committee. ADB Project. (len. Nirman Kunj. indraprastha Estate. 2. 37. RN. Mishra 35.1.dhi Road. 3/5.S. B&R Branch. Sector 55. 4.110030 Chief Engineer (L) Std. New Delhi-I 10011 Prof. 39. Dl-lQ P0. Chief Engineer. 30. Scope Complex. New Delhi Project Director. & Head. L. - Ex-Officio Iix-Officio - CORRESPONDING MEMBERS 1. School of Planning & Architecture. God MR.C. Shukla 13-36. New Delhi Chief Engineer..D. Kothi No. Indian Roads Congress Secretary. Kachhwaha Maj. Kalkaji Extn.. Patparganj. 4. 6. 3. 7. 5. Inlroductiotl Scope I 3 2.IRC:81-1997 CONTENTS Page No. I. Basic Principles of Deflection Method Procedure for Deflection Survey Traffic Analysis of Data tbr Overlay Design Design of Overlay 3 3 13 17 17 << . C. tentative guidelines were published by the Indian Roads Congress under the title “Tentative Guidelines for Strengthening of Flexible Road Pavements Using Benkelman Beam Deflection Technique” IRC:81-1981. Based on the findings of this study and the experience gained over the years with the use of deflection method and other studies carried out in the country.IRC:81-1997 GUIDELINES FOR STRENGTHENING OF FLEXIBLE ROAD PAVEMENTS USING BENKELMAN BEAM DEFLECTION TECHNIQUE I. To lay down a uniform procedure for the design of flexible overlays using the Benkelman Beam deflection technique. The HSS Committee referred this draft back to the newly constituted Flexible Pavement Committee for in depth study. The tentativeguidelines (IRC:81-1981) has been in use since then and based on their application in practice for design of overlays for flexible pavements. 1994. It is widely used all over the World for evaluation of the requirements of strengthening of flexible pavemenLs. Benkclman devised the simple deflection beam in 1953 for measurement of pavementsurface deflection on the WASHO Test Road. the Flexible Pavement Committee prepared revised draft guidelines which were discussed by the Highways Specifications and Standards Committee during the meeting held on 12th May. 1 << . Deflection beam has been in use in India for more than two decades by different organizations. subgradc soil type and moisture and their influence on pavement deflection and service behaviour. INTRODUCT ION A. A research study entitled “Development of Methods such as Benkelman Beam Deflection Method for Evaluation of Structural Capacity of Existing Flexible Pavements and also for Estimation and Design of Overlays for Strengthening of any Weak Pavement” was also undertaken to collect data on pavement deflection values before and after overlaying and various other parameters like temperature. a lot of useful data have been collected and valuable experience gained. Goel (Lt. 1996. IRC (M. 1994 set up a Subgroup with the following members for carrying out the revision of the present IRC:8l. IRC (A.The draft prepared by the subgroup was approved by the Flexible Pavement Committee in its meeting held on i 3th February. Bhatia R.R. 13. Shukla Prof. 1996.Dhir 1.D. 5K. Sunil Bose and Shri Nirmal Jit Singh were also invited to auend the subgroup meetings.E. Sanwal Dr. of Directorate General Border Roads Ex-Offlelo Members President. IRC (S. Kadiyali Prof.P.G.S. 2 .IRC:81-1997 The above committee in its meeting held on 24th May. OP. Pandey Prof. Marathe The guidelines were approved by the Highways Specifications and Standards Cotnmittee in its meeting held on 19th March. P. M. Ganju) Chief Engineer (R) S&R. V. Arya The subgroup held six meetings and discussed at length various aspects of the guidelines in view of the changing loading conditions as well the findings of the Research Project R-6 of MOST.C. AK. S.S. Gupta Prof.K. L.S.K. 1996 and by the Executive Committee in its meeting on 17th April. Jam Convertor Member-Secretary Members Prof.K.S.C. MOST (SC.M. Gupta Prof.K. The guidelines were finally approved by << the Council in its meeting held at Darjeeling on 24th May. Justo Prof. C. A. lain Convenor Member-Secretary Members Prof. Sharma) V. V. Gupta R.1). S.E. Koti Padmakar D. Guram) DG(RD) & Honorary Tteasurer. Rao V. Narain) Secretary. Shri S.R.5.1981. Arora Prof. Dr. Sharma) Corresponding Members Hariom Prak ash SIt am~a MM.Col. Swaminathan Engineer-in-Chief Branch.K. Sharma Prof.13. Batn Dr. livani Prof OP. Jam Rep.P.C. Sood t)r. Justo CS. Srinivasan Prof. CC. C. AHQ I. 1996 (personnel given below).G. Prof.S. Bhatia Shri 1. By suitably placing the probe between the dual whee•••is of a loaded truck. Para 4. 3. 3.66 in long pivoted at a distance of 2. While the rebound deflection is the one related to pavement performance.recoverable deflection of the pavement or because of the influence of the deflection bowl on the front legs of the beam.2. General The deflection survey essentially consists of two operations: (i)condition survey for collecting the basic information of the road structure and based on this. The deformation or elastic deflection under a given load depends upon suhgrade soil type. the demarcation of the road into sections of more or less equal performance.3 discusses the method of deflection measurement and Annexure-1 gives the measuremepi procedure.2.IRC:81-1997 2. it is suggested to all the organisations intending to use the guidelines to keep a detailed tabulated record of periodical deflection measurements (both before and after strengthening).1. 2. and (ii) actual deflection measurements. SCOPE 2. BASiC PRINCIPLES OF DEFLECTION METHOD 3. traffic. Performance of flexible pavements is closely related to the elastic deflection of pavement under the wheel loads. 4. drainage conditions. pavement surface temperature etc. the residual deflection may he due to non. Rebound deflection is used lbr overlay design. Towards this end. its moisture content and compaction. it is possible to measure the rebound and residual deflecüons of the pavementstructure. PROCEDURE FOR DEFLECTION SURVEY 4. These guidelines are meant for evaluating the strengthening requirement of existing flexible road pavements using the Benkelman Beam Deflection Technique. climatic conditions. performance.1. etc. The recommendations are based on the findings of MOST Research study (R-6) and work done at various academic and research institutions in the country as well as the field experience gained over the years in addition to the findings from abroad which are relevant to Indian conditions. the thickness and quality of the pavement courses. Pavement deflection is measured by the Benkelman Beam which consists of a slender beam 3. << 3 .44 m from the tip (see Fig.!). The guidelines may require revision from time to time in the light of future experience and developments in the field.1. type and thickness of overlay provided. 1. Pavement Condition Survey 4. Table I. consists primarily of visual observations supplemented by simple measurements for rut-depth using a 3 metre straight edge.IRC:81 -1997 FIg. Criteria for Classitication of Pavement Sections Classification Good Fair Pavement condition No cracking.2. rutting less than 10 mm No cracking or cracking confined to single crack in the wheel track with rutting between 10 mm and 20mm Poor Extensive cracking and/or rutting greater than 20 mm. Based on these. Sections with cracking exceeding 20 per cent shall be treated as failed. 1. This phase of operation. which shall precede the actual deflection measurement.2. 4 << . Benkelman Beam 4. the road length shall be classified into sections of equal performance in accordance with the criteria given in Table 1. 4. 4. In case the pavement shows severe distress or signs of premature failure further investigations would be necessary to ascertain the causes and design remedial nicasures. The interval between the points should not be more than 50 m. For measuring pavement deflection the C.1.A.2.per cent respectively. 4. A number of metallic blocks of different thickness (measured accurately with a precision 5 << .3. This can he done by using the simple procedure described below: 4.IRC:81-1997 4. highest and lowest values in a group of ten should be compared with mean value. Deflection Measurements 4.3. the measurement points should be &)cm from the pavementedge if the lane width is less than 3. 5 Before. a standard truck having a sear axle weighing 8170 kg fitted with dual tyre inflated to a pressure of 5. the Benkelman Beam should be calibrated to ensure that the dial gauge and beam are working correctly.3. During actual tests. the total load and the tyre pressure are maintained within a tolerance of +/. it will be preferable if the length ofeach section is kept at a minimum of 1 km except in the case of localised failure or other situations requiring closer examination where minimum length of section may be suitably fixed.2.G.5 m and 9() em when the lane width is more than 3.2) minimum often points should be marked at equal distance in each lane of traffic for making the deflection observations in the outer wheel path.. For divided four lane highway.4.5 m from the pavementedge. As it is inexpedient to modify the overlay design at frequent intervals.60 kg/cm is used for loading the pavement. the points marked on adjacent lanes should be staggered. On roads having more than one lane.3 Variability of deflections in a given section should be considered for detecting spots where extra deflection measurements have to be made.1 per cent and ÷/. In this method.5 m.2. the measurement points should be 1. For this purpose.3.R.3.:. 4.third of mean then extra deflection measurements should be made at 25 m on either side of rxnnt where high or low values are observed. If the highest or lowest values differ from the mean by more than one. The beam is placed and levelled on a hard level ground. The data collected during the condition survey shall be recorded as per the Proforma given in Table 2. procedure (vide details given in Annexure-I) which is based on testing under static load may be adopted. starting the deflection measurements. In each road section of uniform performance (see para 4. In the transverse direction. IRC:8l-1997 Table 2 I I I ii i. a S I I I I 1 I I S I ii z I I 6 << .0 In I I. 7. 7 << . The standard temperature and the procedure for correction are discussed in para 4. Dcflections measured by the Benkclman Beam arc influenced by the pavement temperature. In India. If the beam is in order. desirable to conduct deflection measurements during this period.1. For the purpose of applying these guidelines. pavement temperature. a correction factor should be applied.6. For areas in thc country having a’tropicar climate.IRC:81-1997 micrometer) with perfectly plane faces are placed underthe probe and the dial gauge reading recorded each time. 4.. therefore. CorrectIon for Temperature Variations 4. vide para 4. Correction for temperature is not applicable in the case of roads with thin bituminous surfacings (such as premix carpet or surface dressing over a non-bituminous base) since these are usually unaffected by changes in temperatures. Correction need not however.5. The deflection measurements.4. and other information collected during the deflection study should be recorded in the proforrna given in Table 3. the dial gaugeon the beam should read one half the thiclness of the metallic block on which the probe was placed.4. mInimum 40 m). 4. the beam pivot should be checked for free and smooth operation. this period occurs during the recession of monsoon.3. it is intended that the pavement deflections should pertain to the period when the subgrade is at its weakest condition. If the dial gauge is functioning correciiy.).. It is. Otherwise.4. therefore. the dial gauge should be checked arid replaced if necessary. Where the same ~snot feasible. Measurements made when the pavement temperature is different than standard temperature would need to be corrected. For purposes of desiga. it is necessary that the measured deflections be corrected to a common standard temperature. be applied in the latter case if the road is subject to severe cracking or the bituminous layer is substantially stripped. secondly the striking plate beneath the dial gauge spindle should be checked to ensure that it i~ tightly secured and has not become grooved by the dial gauge stylus. Pavement deflections are also affected by seasonal variations in climate. subgrade soil & deflection.e.4. the standard temperature is recommended to be 35°C (also see para 4..4.5. therefore. For design purposes. But temperature correction will he required t~r pavements having a substantial thickness of bituminous construction (i.3. The stiffness ofbituminous layers changes with temperatureof the binder and consequently the surface deflections of a given pavement will vary depending on the temperature of the constituent bituminous layers. all deflection values should be related to a common temperature. 4. 4. 4.2. - Table 3. Available infctmation shows that the deflection-pavement temperature relationship is linear. t.IRC:Sl-l997 4. For example. Correction for temperature variation ~n deflection values measured at pavement temperature other than 35°Cshould’be 0.For convenience in the application of the temperature correction.01 mm for each degree centigrade change from the standard temperature of 35°C.ocation of test point and identification of lane 1 Note: 2 Type of Soil & P1 Moisture content Rebound Dial gauge reading Deflection tnitiai Intermediate Final (mm) 3 4 5 6 7 : : Yes/No 8 9 l’hevalues of pavement surface temperature will be measured at everyhctur during the deflection study 4. if the deflection is measured at a pavement temperature of 37°C. Whether temperature correction is to he applied Whether correction for seasonal variation is to be applied Pavement temperature. preferably when the temperature is uniform uLd is near the standard temperature of 35”C. it is recommended that the deflection measurements in such areas be made when the ambient temperature is greater than 20°C that no correction for temperature need be applied. Accordingly. In colder areas. In the absence of adequate data about deflection. mm.The correction will be positive for pavement temperature lower than 35°C and negative for pavement temperature higher than 35°C.4. and areas of altitude greater than l000m where the average clay temperature is less than 20°Cfor more than 4 months in a year. oftraffic lanes: Date and time orobaen’ation Climatic conditions (hot/humid/cold) Air temperature. Profonna for Recording Pavement Deflection Data Name of Road: Section: No. and 8 << . S.4.performance relationship.above a temperature of 30°C. he correction factor will be 0.No. “C Annual rainrall. as far as possible deflection measurements should be made during morning and evening hours on summer months. ~‘ : Yes/no . 4.4. the standard temperature of 35°Cwill not apply.3. C(’ .01) which t should be subtracted from the measured deflection to obtain the corrected value corresponding to standard pavement temperature of 35°C. it is reeommended that the deflection measurements should be taken when the pavement temperature is within the range of 30°C 35°C.02mm (=2 x . 4. The test pit shall be made good immedialely after taking soil sample and study of pavement composition.soils have been divided into three broad categories.9 m from the pavement edge for single and two lane pavements respectively at a depth of 50 mm to 100 mm below the subgrade level as shown in Fig. topography of the area and road profile. it is always desirable to take deflection measurements during the season when the pavement is in its weakest condition. The measurement should be made at a depth of 40 mm using a suitable short-stem mercury or a digital contact thermometer. 8. suhgrade.1. plasticity index and field moisture content. When deflections are measured during the dry months. Moisture correction factors (or seasonal correction factors) shall be~obtained from Figs. Correction for seasonal variation shall depend on type of suhgrade soil. type of subgrade soil and annual rainfall. in India. Since the pavement deflection is dependent upon change in the climatic season of the year. A soil sample of weight not less than 100gm should he collected using an auger from the subgrade underneath the dellection observation points i. Since. 0.S.6 m and 0. 2 to 7 for given field moisture content. 9 << .5. its field moisture content (at the time of deflection survey) and average annual rainfall in the area. deflection measurements should be confinedto this period as ft~ras possible.5. For this purpose a test pit at the shoulder (adjacent 10 pavement edge) shall be dug to a depth upto 15 cm below the subgrade level in every kilometer depending on the uniformity of suhgrade soil. In cases where temperature correction is to be applied. the pavement temperature should be measured during the deflection survey. namely low rainfall (annual rainfall 1300 mm) and high rainfall (annual rainfall >1 3(X) mm). 4. Correction for Seasonal Variation 4.IRC:81-l997 4.2.5.5. rainfall has been divided into two categories. this period occurs soon after monscx)n. they will require a correction factor which is defined as the ratio of the maximum deflection immediately alier monsoon to thai of the minimum deflection in the dry months. 4 The soil sample for determination of suhgrade type and its field moisture content shall be scooped from below the pavement as shown in Fig.e. a hole of about 45 mm deep and about 10 mm diameter should be drilled in the pavement and filled with glycerol and temperature can then be recorded after about 5 minutes. clayey with low plasticity (P1 15) and claycy with high plasticity (P1 > 15). Similarly.4. For this purpose. The suhgrade soil shall be tested as per IS-2720 for type of subgrade soil. For this purpose. namely sandy/gravelly. IRC:8 1-1997 36 1 32 25 2 24. S FIg. 211 tJ~JTh HLD 1~ 5516160 LDN~1Nl N Fig. 3. MoIsture correction factor for Sandy/Gravelly soil subgrade for low rainfall areas (Annual rain#all S 1300 mm) 1 54 I 40 2 I 32 N 1 25 N Is. 2. 1 20 1 2 105 M2IS1UCE CONILN1. Moisture correction factor for Sandy/Gravelly subgrade for high rainfall areas (Annual rainfall > 1300 mm) 10 << . ~ < 22 Fig. 4.W . 5.2 1.2 2.0 I I II I JI[]IJIIDhTI1TT~ 4 b 10 12 4 16 ~8 . 12 14 15 15 20 MOISTURE CONTSNT.4 C 0 2 . Moisture correct.6 0 C) SI IC 15 0 U SI :2 10 0 5 10 I i I~b. Moisture correction factor for clayey subgrade with low plastklty (P1 areas (Annual rainfall >1300mm) 15) for high rainfall Ii << .22 M0I~TURtCONTENT 1~) < Fig.Ion factor for elayey subgrade with low plastIcity (Pt areas (Annual rainfall 5 1300 mm) 22 15) for low rainfall 2.IRC:81-1997 2.) 1.0 IC 0 18 IC 0 U Sr 16 0 6.0 IC 0 1) C IC 1. S Fig.4 0 MOISTURE CONTENT.2 2.IRC:81 1997 2. 6. 0 U Sr 3 10 0 MOISTURE CONTENT. 7. Moisture correction factor for clayey subgrade with high plasticity (N> 15) for low rainfall areas (Annual rainfall 5 1300 mm) Sr 0 . Moisture correction factor for clayey subgrade with high plasticity (Pt> 15) for high rainfall areas (Annual rainfall > 1300 mm) 12 << .5 0 U Sr Sr 1.0 SI — 0 18 IC 0 U Sr Sr 16 0 U SI LI 1. S Fig. —PIT TO BE CUT ON S~DE OF’ PAVEMENT UPTO 50cm BELOW SUB BASE LEVEL 2 0 FIg. To obtain a realistic estimate of design traffic due consideration should be given to the existing traffic. 5.4 below. TRAFFIC Traffic in terms of million standard axle shall be considered for the design of overlay. possible changes in road network and land use of the area served. << 13 . The deflection values corrected for temperature shall be multiplied by the appropriate values of seasonal correction factors to obtain corrected values of deflection.1.4.5. only the number of commercial vehicles of laden weight of 3 tonnes or more and their axle loading will be considered. The traffic is considered in both directions in the case of two lane road and in the direction of heavier traffic in the case of multi lane divided highways. otherwise design traffic may be calculated as per the procedure given in IRC:37 and pam 5. General For purposes of the design. the probablegrowth of traffic and design life. 8. 5.IRC:81 -1997 ~lNOUS LAYERS — if/ . If sufficient data are available at the stretch with respect to the wheel load distribution of commercial vehicles or the vehicle damage factor and their transverse placement. thecumulative standard axles may be worked Out based on actual data. The annual rainfall data has to be obtained for that’particular area. Determination olfield moIsture content using auger 4. 3. in exceptional cases where this information is not available 3-day count could be used. Elasticity of transport demand.. it is recommended that an average value of 7. The design traffic is considered in tenns of the cumulative number of standard axles to be carried during the design life of the road.3.4.4.5 per cent may be adopted for roads in rural routes. (1) A The cumulative number of standard axles to he catered fOr tO the design Initial traffic. in tcmls of the number of commercial vehicles ~xr day duly modified to aecsslnt for lane distritiutisas as explained in paragraph 5. in the year of completion of constmctirsi. Computation of design traffic 5. Design life It is recommended that the design life for strengthening of major roads should be atleast 10 years.2. The following equation may he used to make the required calculation 365 x where. lateral distribution of traffic.2.1. Less important roads may. = a = = F << 14 . 5. If adequate data is not available. 5. normally be based on 7-day 24-hours classified traffic counts. the design life in years and the vehicle damage factor (number of standard axle per commercial vehicle) to convert commercial vehicles to standard axles. = = A l(1+rf - II xF . However. Tralflc growth rate An estimate of likely growth rate can be obtained as follows: a) b) c) By studying the past trend in traffic growth. N.4. 5. Annual growth rate of commercial vehicles Design life in years Vehicle damage factor (numher of standard axles ~r commercial vehicle) refer to paragraph 5.IRC:S 1-1997 Estimate of the initial daily average traffic flow Ibr any road shoult. however.4. the growth rate. Its eoniputation involves estimates of the initial volume of commercial vehicles per day. he designed for a shorter design period but not loss than 5 years in any case. (i) Single-lane roads (3. (iii) Four-lane single carriageway roads The design should be based on 40 per cent of the total number of commercial vehicles in both directions.75 m width) Traffic tends to be more channelised on single lane roads than on two lane roads and to allow for this concentration of wheel load repetitions. Ex: For dual three-lane carriageway distribution factor .2. the design should be based on the total number of commercial vehicles per day in both directions multiplied by two. However.IRC:8 1-1997 5. The design will normally be applied over the whole carriageway width.4. if in a particular situation a better estimate of the distribution of traffic between the carriageway lanes is available from iraffic surveys~~. (iv) Dual carriageway roads The design of dual two lane carriageway roads should be based on 75 per cent of the number ofcommercial vehicles in each direction. The distribution fader shall be reduced by 20 per cent for each additional lane. DistributIon of commercial traffic over the carriageway A realistic assessment of distribution of commercial traffic by direction and hy lane is necessary as it directly affects the total equivalent standard axle load ‘applications used in the design.d lane. same should be adopted the and the design is based on the traffic in the most heavily trafficke. (ii) Two-lane single carriageway roads The design should be based on 75 per cent of the total number of commercial vehicles in both directions. It is recommended that for the time being the following distribution may be assumed for design until more reliable data on placement of commercial vehicles on the carriageway lanes are available. Where significant difference between the << 15 .60 per cent The traffic in each direction may be assumed to be half the sum in both direclions when the Iatteronly is known. 5 4. The vehicle damage factor is arrived at from axle-load surveys on typical road sections so as to cover various influencing factors such as traffic mix.15(X) more than 1500 3.5 << 16 . the condition in the more heavily trafficked lane should be considered for design. Where sufficient information on axle load is not available. 5. time of the year.5 1. The AASHO axle load equivalence. lndlcatl~e VDF Values Initial traffic intensity in temis ofnumber of commercial vehicles per day (Traffic range) Terrain Rolling/Plain 1. The designer should take the exact value of VDF after conducting the axle load survey particularly in the case of major projects. terrain. State Highways and MDR’s which reveal excessive overloadng of commercial vehicles.IRC:81-l997 two streams can occur. type of iransportation.5 0-150 150. the same should be adopted and the design is based on the traffic in the most heavily traffic lane. However. the tentative indicative values of vehicle damage factor as given in Table 4 may he used.3. factors may be used for converting the axle load spectrum to an equivalent number of standard axles. road condition and degree of enforcement.5 • Hilly 0.4. the vehicle damage factor should be arrived at carefully by using the relevant available data or carrying out specific axle load surveys depending upon importance of the project. VehIcle damage factor The vehicle damage factor (VDF) is a multiplier for converting the number of commercial vehicles of different axle loads to the number of standard axle-load repetitions. Table 4. type of commodities carried. For designinga strengthening layeron an existing road pavement. Some surveys have been carried out in the country on National Highways.5 2. The design will normally be applied over the whole carriageway width. if on a particular situation a better estimate of the distribution of traffic between the carriageway lanes is available from traffic surveys. IRC:81 -1997 6.. standard deviation and characteristic deflection. The design curves relating characteristic pavementdeflection to the cumulative number of standard axles to be carried over the design life is given in Fig. The formulae to be used in the calculation are as follows: Mean Deflection. mm Characteristic deflection. (2) _________ fl - . — X = — . men Mean defiection.1.mm Number o deflection meaturemenra Standard deviation. ANALYSiS OF D-ATA FOR OVERLAY DESIGN ~. (1) Dr= ~+2r ‘for major arterial roads (like NH & SH) (ii)Dc= it + a for all other roads where X = = = = = n a Dc Individual deflection. 7. Overlay design for a given section is based not on individual deflection values but on a statistical analysis of all the measurements in the section corrected for temperature and seasonal variations. Characteristic Deflection. This involves calculation of mean deflection.1.9. 7. Characteristic Deflection 6.l.2.1. The characteristic deflection (Dc) value to be used for design purposes will be the same as given in equations (4) and (5).. The characteristic deflection for design purposes shall be taken as given in equations (4) and (5). mm These shall be recorded in the Proforma suggested in Table 5. Standard Deviation. DFSIGN OF OVERLAY 7. This will be determined as per the procedure given in Para 6.1. 17 << . IRC:8l-l997 Table 5 21 p I ii ~.. H It I i ~ I L~ a ‘I I ‘lIt ID U << 18 . 9. mm Fig.IRC:8l-1997 400 300 I: E 0 > C) ~ 0 LI 0 200 :3 0 c E :3 00 Chorocter~stkDeflection. Overlay Thickness Design Curves 19 << . Before implementing the overlay. the equivalent overlay thickness to be provided may be determined using appropriate equivalency factorsas suggested below: cm of Bituminous macadam = 1. the recommended minimum bituminous overlay thickness isSO mm bituminous macadam with an additional’surfacing course of 50 mm DBM or. 7. 20 << . pot holes.5. 9 is the overlay thickness in terms of bituminous macadam construction. For heavily trafficked roads.8. the existing surface shall be corrected and brought to proper profile by filling the cracks. The thickness of wearing course should be in conformity with IRC:37. In case other compositions are to be laid for strengthening.3. The type of material tobe used in o’~’erlayconstruction will depend on several factors such as the importance of the road.40 mm bituminous concrete. ruts and undulations. 7. The thickness deduced from Fig. The design traffic in terms of cumulative standard number of axles will be computed as per the procedure described in Para 5. Where structural deficiency is not indicated from deflection values.5 cm of WI3M/Wet Mix Macadarn/BUSG 0. the design traffic. No part of the overlay design thickness shall be used for correcting the surface irregularities. construction convenience and relative economics.4. From structural considerations. 7. thin surfacing may be provided to improve the riding quality as required.6.IRC:81-1997 7.7 cm ofDBM/AC/SDC I cnt of Bituminous macadam = 7. 7. it will be desirable to provide bituminous overlays.7. the thickness and condition of existing bituminous surfacing. << 21 .A. For dividcd four lane highway. The use of tyres with tubes and rib 20. the point should be located 60cm from the pavement edge if the lane width is less than 3. equipped with dual tyres.60 kg/cm Tyre pressure measuring gauge Thermometer (0-100°C)with 10 (3) (4) (5) Procedure (I) division A mandral for making 4.25 cm and at bottom 1 cm. METHOD) SCOPE This method of test covers a procedure for the determination of the rebound deflection of pavementunder static load of the rear axle ofa standard truck. Spacing between the tyre watts should be 30-40 mm. The point on the pavement to be tested is selected and marked.R.IRC:81-1997 Annexure-I STATIC LOAD DEFLECTION TEST PROCEDURE (C. For highways.5 cm deep hole in the pavement for temperature measurement. The dsameter of the hole at the surface shalt he 1. 12 ply inflated to a pressure of5. The tyres shall be lOx treads is recommended. EQUIPMENT The equipment shall includc~ (1) Benkelman ilearn (a) (b) (c) (d) Length ofprobe arm from pivot to probe point Length ofmeasurement arm from pivot to dial Distance from pivot to front legs Distance from pivot torear legs 244 cm 122cm 25 cm 166cm 33 cm (e) (2) Lateral spacing of front support legs A 5 tonne truck is reenmmcndcd as the reaction. The vehicle shall have 8170 kg rear axle load equaUy distributed over the two wheels.5 m and 9(1 cm from the pavement edge for wider lanes.5 in from the pavement edge. 2. the measurement points should he 1.G. the actual pavement (2) (3) If the differential readings obtained do not compare to 0. CALCULATIONS (I) Subtract the final dial reading frsmns the initial dial reading.025 mm per minute. i’he beam pivot arms are checked for free movement. The truck is driven forward a further 9 m. (4) (5) (6~ The truck is slowly driven a distance of 270cm and stopped. The tocking pin is removed from the beam and the legs are adjusted so that the plunger of the beam is in contact with the stem of the dial gauge.025 nun per minute. twice the final differential dial reading represents apparent pavement denectiun.) is recorded atleast once every hour inserting thermometer in the standard hssle and filling up the hole with glycerol. The dial gauge is set at approximately I em. (8) (9) (10) Pavement temperature (see para 4. Also subtract the intermediate reading from the initial reading.am is inserted between the duals and placed on the selected point. The probe of the Benketman be. if necessary. (II) The tyre pressure is checked at two or three hour intervals during the day and adjusted to the standard. If the differential readings obtained compare within 0. (7) An intermediate reading is recorded when the rate of recovery of the pavement is equal to or less than 0.4.025 mm per minute.025 mm. << 22 .IRC:81-l997 (2) (3) The dual wheels ofthe truck are centered above the selected point. The final reading is recorded when the rate of recovery of pavement is equal to or less than 0. The initial reading is recorded when the rate of defomsation of the pavement is equal or less than 0.025 mm deflection is twice the final differensial reading. IRC:8 1-1997 (4) Apparent deflections are corrected by means of the following fonnula XT=XA-+-2. 9 of Table 3) shall be the tssice of the Xi value. (5) The rebound deflection (%) (i. << .e. twice the difference between the final and intermediate dial readings.9l Y in which Xi = ‘l’nse pavensent deflection XA = Apparent pavement deflection = Vertical mssvement of the front legs i.e. en!.