FUNCTIONAL REQUIREMENTS AND EVALUATIONOF PAVEMENTS FUNCTIONAL REQUIREMENTS OF FLEXIBLE PAVEMENTS Requirements of Road Users The road pavements have to be constructed and maintained in such a way that they fulfil the functional requirements of the road users, to provide safe, comfortable and fast movement in their vehicles at reasonably low vehicle operation cost. The common road users, judge the functional requirements of a road pavement in terms of riding comfort; they may also recognise the importance of fast movement and ability to stop the vehicles on applying brakes, without undue skidding; however majority of the road users may not be aware of the increase in the vehicle operation cost due to pavement undulations. Therefore the functional requirements of the road pavements from road users point of view may be summed up as: The pavement surface should not become too slippery during service life or in other words the surface should retain sufficiently high skid resistance value for safe operation at design speed including stopping requirements, under adverse surface conditions. The pavement surface should be even along the longitudinal path to provide good riding quality for vehicles moving at the design speed. The unevenness and longitudinal undulations cause vertical oscillations in moving vehicles, resulting in poor riding comfort. The transverse profile of the pavement should be retained with appropriate camber or super elevation during the design life, without too much o permanent deformation of pavement surface along the wheel path in the form of ruts. In other words, the rut depth should not be excessive, as this could affect the riding quality, especially in the case of fast moving operations. The pavement surface should not be permitted to develop cracks as this is a clear indication of the pavement distress that has started developing. These cracks permit easy flow of water from the surface in to the pavement layers and the subgrade, resulting in the rapid deterioration of pavement due to the combined effects of traffic loads and environmental effects. The pavement surface should not be permitted to develop pot holes. If the pot holes are properly patched as soon as they start developing, the pavement life could be prolonged considerably. If the potholes left unattended, they become larger in size and depth, resulting in the breaking up of pavement with the need to take up rehabilitation measures. The riding quality of pavement surface should not be affected by the other types of surface disintegration in the form of spalling, ravelling or stripping. 1 Therefore it is desirable to provide an even or plane surface with least undulations or unevenness. thus resulting in less safety or more risk at any speed. stripping. It is desirable to investigate the actual type of cracking and possible remedial measures. Rutting Excessive rutting causes discomfort to fast moving vehicles.Skid Resistance In order to allow for safe speed reduction and stopping. or to provide safe traffic operation. the braking distance required will be high. EVALUATION OF PAVEMENT SURFACE CONDITION Skid Resistance When vehicles moving at high speeds apply brakes to slow down or to stop. may occur. Various other types of failures or pavement distress such as ravelling. the friction between the tyre and the pavement surface is called in to play. the vehicles are subjected to vertical oscillations of varying magnitude and frequency. Other Surface Defects The fine hair cracks that develop on bituminous pavement surface should be taken as a caution signal indicating the start of pavement distress and deterioration. all of these decrease the riding comfort and the riding comfort and performance assessment by the road user. particularly during lane change and in overtaking operations.. etc. Excessive rutting also indicates deterioration of structural condition of the pavement. increase in discomfort to the passengers and higher rate of fatigue to the drivers and other occupants of the vehicles. If the coefficient of friction or the skid resistance of the pavement surface is low. Therefore one of the important components of 2 . Therefore the rutting of pavement surface may be limited to a desirable limit. Longitudinal Surface Profile If the longitudinal profile of the pavement surface is undulated or uneven. causing increase in fuel consumption in vehicles. the wheels would correspondingly skid along the pavement surface and maximum possible friction is developed. the road surface should have sufficient skid resistance under the adverse pavement surface conditions. If attempt is made to partially or fully lock the wheels by applying brakes. the skid resistance of pavement surface should be uniformly high and the variation in the skid resistance across and along the pavement should be minimum. increase in wear and tear of all moving parts and in the tyres. Therefore from safety requirements. when automobiles travel at high speed. bitumen content etc. the factors such as the tyre surface characteristics ( treaded or smoothened /bald ). also are some of the important factors.the road user related pavement evaluation is evaluation of road safety in terms of skid resistance measurement. this decrease is prominently seen pavement surface. However the tread pattern and type of tyre may not have significant influence on skid resistance of pavement. etc. age of pavement. tyre pressure and load on the tyre could affect the skid resistance. Pavement Surface Condition The skid resistance of a pavement surface varies depending on wheather the surface is dry or is clean and wet or there is snow or ice or mud or oil or dry sand on pavement surface . construction and maintenance practices.. aggregate-polishing value. affect the macro texture of the pavement surface. particularly on the wet pavement. bituminous surface. Other Factors The other factors which affect the skid resistance of pavement are temperture. The properties of the mix such as gradation. degree of brake application. cement concrete surface. (open graded or dense graded). which in turn affects the skid resistance. and their surface finish affect the skid resistance. speed. etc Methods of Measuring Skid Resistance The method of measurement of skid resistance may be divided in to three groups: i) Laboratory methods ii) Methods using portable equipment iii) Semi field model tests using mounted vehicle test iv) Dynamic test methods on actual 3 . The presence of these materials on pavement surface could cause reduction in skid resistance to different degrees depending on several factors including the macro texture of the pavement surface. Speed Speed of the vehicle and braking efficiency or extent of locking affects the skid speed. traffic and its smoothening effect on pavement surface along the wheel path. Usually the skid resistance is found to decrease with skid speed. etc. Tyre Characteristics As the friction depends on the tyre pavement interface. The type of the aggregates and the characteristics such as micro texture. shape etc. Factors Affecting Skid Resistance Type of pavement Surface Different types of pavement surfaces such as WBM. pavement surface and v Test vehicle method. resulting in oscillations. Bangalore University. The increase in the cost may be due to a) increase vehicle operation cost b) increase in the travel time and consequent increase in time cost of vehicle and time cost of passengers. measured in terms of angle. the losses due to uneven pavements of National Highways in India in terms of increased vehicle operation cost is in the order of Rs 200 crores per year. Dynamic Trailer Type Skid Resistance tester is a very useful equipment for high speed testing of pavement surface. its weight. It was estimated by RUCS that based on 1982 price level. it slides through specified length of the test surface. Pavement Unevenness (Roughness) The serviceability of a pavement is largely a function of its unevenness.. it is possible to determine the skid resistance tester working on a slightly different principle has been designed and fabricated at the Department of Civil Engineering. Types of Undulations The undulations or unevenness of pavement surface may be classified in to three categories: i) rough surface profile with minor corrugation which cause some discomfort and vibrations. especially in light vehicles ii) uneven surface with small depressions and humps resulting in considerable discomfort due to oscillations which depend on the vehicle type. tyre size. suspension details and speed. c) increase in the intangible costs such as early fatigue of drivers. On stretches with the above type of pavement surface. The pavement undulations imparts acceleration to the vehicles and the passengers. discomfort of passengers and higher accident rates. Of the various test methods. increase in fuel consumption wear and tear of the tyres and moving parts of the vehicle and discomfort to the passengers. a few of the most commonly used methods are given below: Portable Pendulum Type Tester This is a very simple portable test method which can be used for testing specimens in the laboratory or for conducting in situ tests over existing pavements. Studies made at the AASHO road test have shown that 95% of the information about serviceability of a pavement s contributed by the unevenness of its surface profile. The dynamic Fifth wheel Type Skid Resistance Tester has several advantages over trailer type and this equipment has also been designed and developed at Department of civil Engg. loses some energy due to the frictional resistance and hence swings and rises to a lower height on the other side. From this loss in weight. When the pendulum arm with the test rubber fixed on the shoe of the pendulum is released. the small vehicles 4 . along with other necessary instrumentation. The road User Cost study (RUCS) conducted in India has revealed that there is a large wastage in the form of increased road user costs in the country due to bad and uneven / undulated pavement surface on most of the highways. are subjected to considerable discomfort even at low speeds. particularly due to settlement of embankment or its foundation. drainage and environmental factor. Causes and Remedial Measures Often the major contributing causes for unevenness in pavement are poor or inadequate sub surface drainage. Factors on Affecting Unevenness (Roughness) The formation of unevenness on pavement surface is due to the combination of reasons which include defects and short comings in the design. inferior subgrade soil. Methods of Evaluation of Unevenness The evaluation of undulations or unevenness in the pavements may be divided in to three broad classifications: 5 . use of boulder or brick soling etc. The first step before trying any remedial measure to deal with the undulations of pavement surface is to carry out investigations and identifications of the actual causes for the situation. If the defect is limited to the problem in top layers ( in the form of surface corrugations). But the common large scale undulations in pavement surface in the form of unevenness due depressions and humps of larger magnitudes causing increase in vehicle operation cost and considerable discomfort to passengers of automobiles may be due to the problems at the subgrade level. in adequate pavement thickness unscientific construction practices ( such as improper compaction of subgrade. iii) uneven surface with large scale depressions. The common defective practices prevalent in India such as subgrade not being adequately compacted during initial construction and the use of boulder stone or bricks on edge as soling or foundation course (which results in non uniform settlement of this lower sub base layer because of lack of interlocking between the stones or bricks) are the primary causes for such undulations. The size of the undulation (magnitude and amplitude) could give an indication regarding the depth at which the problem has started. The development of corrugations on the surface may be due to defective materials or construction of top layers. construction and quality control in road construction. as a levelling course followed by a resurfacing layer of appropriate specification is likely to provide a fairly satisfactory pavement surface. the remedy is also relatively simple.0 m length. subgrade soil type and traffic loading.) and excessive magnitude of load and their repetitions with reference to the pavement structure. However such profiles will be of very great importance for high speed movement of vehicles such as on high speed highways and runways. the depressions could be negligibly small. The formations of large waves may be generally due to the differential settlement of the embankment fill material or the embankment foundation itself. There may not be noticeable minor undulations in such cases and hence under a straight edge of 3. There are large number of equipment developed by various organisations based on the principle of moving straight edge or moving datum resting on two pairs of wheel which rolls or traverses along the pavement surfaces and this vertical movement ( up and down ) with respect to thr temporary datum is utilised to indicate or to measure unevenness. The straight edge method is also a very slow and cumbersome method of evaluation. The straight edge ( usually of 3. The development of multiple wheel profilometers is considered to be a definite improvement to overcome this draw back.5m length). When placed on the pavement surface tests. which is a single wheel trailer unit. The equipment using this principle. for checking the finished pavement layers soon after the construction. etc) and grouped. Methods Based on Physical Measurement One of the oldest methods of measuring undulations on the surface is by observing the spot levels with reference to reference datum. Methods which are based on certain physical measurement of the surface undulations. the vertical oscillations of which is integrated while hauled by a vehicle at specified speed is the most commonly used methods to evaluate the undulations in terms of unevenness Index value in mm/km. Use of straight edge for measurement of unevenness is very simple method which has been specified by the Indian Roads Congress. Methods which are based on indirect measurement in terms of human response to surface undulations during riding. 8 to 10. 6 . Other type of equipment which was used in AASHO road test is for the measurement of variation of the slope values of a unit mounted on a pair of wheels. This is very slow and tedious method and interpretation of evaluation of common pavement undulations is difficult. However moving datum resting on two sets of wheels does give a relatively steady datum for obtaining a fairly reliable data of undulations. Methods which are based on subjective assessment or rating of the surface characteristics and no measurement is involved. The depressions are then classified ( such as 6 to 8. The Bump integrator.on the top of the highest spots or humps of the surface and the depression below the straight edge are measured in mm using a wedge scale or vertical bit of scale. However this method is ideally suited to evaluate large size waves on highway and runway pavements which can not be measured by other methods. available in India ( CRRI design) are the unevenness indicator and profilograph.0m length and in some cases of 4. 91 log (0.) +( B1 D1 + B2 D2 + …….91 log ( 1+SV) – 1.01 C+P 7 .Indirect Measure Method The principles of indirect response method is by psycho. Present Serviceability Index ( PSI) Pavement serviceability measurement in terms of PSI is subjective assessment of pavement surface condition. The rating is done based on subjective point rating scale. R1 is a function pavement unevenness or slope variance.physical approach. One of the typical equations developed after the AASHO road test for pavement serviceability of flexible pavement is given by: PSI = 5. Huchinson developed the technique of ‘Tracking Task’ and the tracking error is used for the evaluation of pavement undulations and this has been correlated with Present Serviceability Rating of the pavement. The most commonly known approach is the development of PSI equation in the form PSI = C+ ( A1 R1+ .03 – 1.4 R – 30) .38 ( RD)2 – 0. B2 … are coefficients.01 C+P = 5. ASSESSMENT OF FUNCTONAL REQUIREMET Physical Measurements The commonly used physical measurements for surface condition or functional evaluation of the pavement are Unevenness Index or slope variance along the wheel paths Rut depth along wheel paths Cracking (percentage of cracked area or length of classified cracks per unit area) Present Serviceability Rating ( PSR) The PSR value is obtained by the rating panel in five point rating scale or a ten point rating scale after classifying the qualitative ratings as very poor..38 (RD)2 – 0. The mean value of individual value is taken as PSR. good and very good.03 – 1. B1. poor. ……. But the method such as uneven index measure method is an objective assessment. fair.) Where C. The rating values have also been correlated with the evaluation using physical measurement of pavement surface.1. A1. D1 is a function of rut depth of surface and D2 is a function of surface deterioration expressed in terms of cracking and patching. Rating Technique A trained team is utilised to rate the pavement serviceability either by visual rating or by riding in a test vehicle. the pavement condition indicator or the values of PSI are made use of. Law Model 690 Digital Non Contact Profilometer French APL Longitudinal Profile Analyser South Dakota DOT Profilometer 8 . the common methods of measuring pavement surface undulations prevalent in India are by: Straight edge Spot Levels Unevenness indicator Profilograph Unevenness Integrator or Bump Integrator Some of the other sophisticated equipment available in other countries are: K.Applications of Present Serviceability Index / Pavement Condition Indicator In Pavement Design The AASHO method of flexible pavement design introduces the user definition of pavement failure in terms of serviceability Pt at the end of the time.5 The Asphalt Institute method of designing full. In the basic thickness relationship. the cut off region indicating failed condition of each pavement / curve is decided based on the PSI COMMON METHODS OF MEASURING SURFACE UNDULATIONS The methods of measuring pavement surface undulations can be broadly classified in to two groups viz. By physical Techniques By Indirect Techniques Under Physical Technique.5 In Overlay Design For deciding allowable deflection and failure criterion for the development of the design overlay design chart. t rather than based on the strict structural failure concept..0 to 2.5 to denote failure.depth asphaltic pavement makes use of the asphaltic pavement performance serviceability concept provided by the AASHO road test results by selecting a terminal serviceability of 2. T= a0 + a1 log W + a2 L1 + a3 L1 L2. W is the load application in terms of standard axle load to serviceability Pt = 2.J. In the charts which are developed with corrected characteristic deflection values from the Benkelman beam rebound deflection studies versus cumulative standard axles for different values of initial deflection. The commonly used terminal value of PSI on Pt = 2. it is possible to obtain all the types of undulations of the pavement surface. When the straight edge is placed on the pavement surface. soon after construction as part of quality control measures.J.0 metres apart and the probe wheel placed in between the datum wheels moves up and down relative to the temporary datum. it rests over the high spots along the line ( in the longitudinal or transverse direction of the pavement) and the undulations measured are in the form of depth of depressed portion of the pavement surface below the bottom of the straight edge which is taken as the reference line or the temporary datum.The datum line does not represent an absolute datum or reference line as the depth of certain depression at a spot of pavement depends both on the length of the straight edge used and its relative location on placement over the spot under consideration. Using the spot level values and distances. Law 8300 Roughness Surveyor Dynatest 5000 Roughness Distress Meter ROMDAS ( ROad Mesurement Data Acquisition System) Straight Edge Method The plain sliding straight edge is probably the oldest and simplest method. Unevenness Indicator Developed at CRRI has a moving datum resting on two sets of datum wheels 3. including very large size waves which can not be measured by ordinary methods using 3. and the actual surface profile of the pavement could be plotted. This is very convenient and rapid method especially for locating or for making the spots having undulations more than the 9 . Spot Level Method Spot level measurements ( using a levelling instrument and levelling staff) along the desired line on the pavement surface at known distance intervals could br used to evaluate the undulations of pavement surface. The vertical movement of the probe wheel ( both humps and depressions) could be measured with the help of the pointer and calibrated dial. it is possible to represent the undulations in terms of slope variance as one of the parameters required to evaluate the riding quality of two pavement.0 or 4.0 m long straight edge has been recommended by the IRC. Automatic Road Analyser or ARAN Portable Universal Roughness Device or PURD Swedish Laser Road Surface Tester K. the field work and the method of measurement by the straight edge is tedious and time consuming. the references datum line is at a fixed level and therefore the undulations noted are absolute values with reference to the fixed datum. However.5 m straight edge in some cases. Except minor corrugations of the surface. for checking the surface of the new pavement layers in general and 4.5 metres straight edge or other moving datum type of instrument. Since the spot level observations are with reference to a bench mark. In India a 3. Though this is a useful instrument developed in India this is not being commonly used for evaluating the unevenness of the pavement surface. However. Measurement of Pavement Unevenness Index by Using Bump Integrator ( Roughometer) This device was originally described at the annual meeting of Highway Research Board in 1940 and has since remained unchanged apart from various mechanical modifications. In addition. both counters being located in the towing vehicle. During testing. the unit is towed at a constant speed of 30 kmph and the uni directional vertical movements of the wheel with respect to the chassis are totalised by an integrator unit and is recorded in inches on an electromagnetic counter. The vertical motion of the wheel is damped by two large dash pots. Distance is measured by recording the wheel revolutions on another counter . to full size scale and the chart moves as the instrument is hauled forward and the horizontal scale obtained is 1 in 200. the probe wheel placed in between the datum wheels moves up and down relative to the temporary datum. Profilograph Developed at CRRI also is an equipment mounted on two sets of datum wheels 3. the profile of the pavement surface as sensed by this trailer unit is also recorded on a chart. A modified version of this unit was developed at the CRRI. After traversing the given length of stretches of road both integrated undulation reading and wheel revolution reading in the eletro magnetic counters are to be recorded.desired limit particularly during construction of pavement as part of quality control checks and also for patch repair work during maintenance work. the bump integrator trailer unit is to be attached to a vehicle and is hauled along the desired wheel path of test stretches four to five times at a uniform speed of 30 km sped. the wheel being supported in a heavy chassis by two single leaf springs on ball bearing shackles. Also the bump integrator readings from the counter are generally in inches per test 10 . London. The unit comprises of single wheel trailer. the inherent limitation of the moving datum mounted on two sets of datum wheel causing frequent changes in the datum or references line is inevitable and this limitation is present in all such equipment. To evaluate the unevenness index values of the given stretch of the road. Significant mechanical improvements to the original equipment were carried out by Road Research Laboratory. In this equipment.0 meters apart. The readings obtained from the field study may not represent the unevenness index per km length. The vertical movements are graphically recorded on a chart to indicate the undulations relative to the temporary datum. as the test stretch may be lesser or more than one km. 11 . although this is not / absolute value as the instrument tends to show high response on those irregularities that are ironed out by its springs ( large spring movement) and low response on those not ironed out by its springs ( small spring movement). Hence it is necessary to convert the readings obtained from the field in to cm/km or mm/km. Limitations of Equipment Variation in results are likely due to the following reasons Suspension of trailer unit: The stiffness and condition of the spring and dash pots in the suspension affect the measured values. change in tension or snapping of the cord. Also the performance of the dashpots is very sensitive to the fluid level. The device offers a rapid means of measuring unevenness or riding quality. Dash pot fluid: The viscosity of the dash pot fluid causes variations damping effects and therefore variation in results. reset to zero not functioning. etc. Applications The bump integrator provides a measure of the work done by a vehicle suspension in traversing a road and hence is an indication of the extra energy required or the extra cost to the travelling community caused by unevenness. The following relation may be used: UI= ( B/W) x R x 2. so that the field work can be completed quite fast without any hindrance to the movement of traffic like other slower devices. Road Wheel: If the radius of the working wheel gets altered due to wear and tear of the tyres. wear. erroneous results are likely to occur in the unit. there is a possible variation in unevenness index values as well as in the calculation of length of stretch from the number of revolutions. Variation in fluid level in the dashpots causes variations in the measured values of unevenness index Load: If the standard weight of the unit gets altered. cm/km B= Bump readings from the field ( after initial setting to zero) R= Number of revolutions per km ( 460) W= Number of wheel revolutions from the field. Consistent results can be obtained if unit is operated correctly. Therefore it is necessary to have sufficient knowledge about the unit such that the defects could be checked and rectified in time.54 Where UI= Unevenness Index. internal slipping and run on. and the simple numerical output is easy to handle for long lengths of road where a graphic record is tedious to evaluate. Integrator: Some inherent problem are associated with the integrator unit namely. the unevenness readings are also likely to be affected.stretch. It also provides a measure of riding quality or passenger comfort. Due to any such defects. Rating technique is an indirect method adopted for the assessment of riding quality of the pavement surface. Earlier. The rating may be done either by visual inspection of the pavement surface or by assessing the riding quality of road by travelling in a test vehicle at the desired test speed. that is. color. patching. a pavement was considered to be either satisfactory or unsatisfactory which is in the need of repair or replacement. who is influenced by several attributes of the pavement including the following: Response to motion as characterised by the particular pavement vehiclehuman interaction for particular speed. Many popular design systems involve determination of the pavement thickness required to hold certain set of computed stresses or strains below some specified levels. Serviceability must be defined relative to the purpose for which the pavement is constructed. but not much information was available prior to AASHO road test to relate such pavement distress to functional behavior. The notions of a stimulus continuum and a judgement continuum must be introduced to comprehend the principles of psychophysical measurement. little attention was paid to the evaluation of pavement performance. A stimulus or physical continuum refers to changes in some 12 . In other words measurement should relate explicitly to the user. which is essentially a subjective evaluation. to give an even comfortable and safe ride. shoulder conditions etc. The ideas of relative performance were not adequately developed. did not consider the level of performance desired. Until the pavement serviceability concept was developed during the AASHO road test. Thus a method of performance evaluation was badly needed for the use in the pavement engineering at the time of AASHO road test and it was fulfilled with the Serviceability Concept developed by Carey and Irick. The assessment of the riding quality is considered to be the most important component of the pavement surface condition evaluation. Response to appearance.PAVEMENT SERVICEABILITY CONCEPTS The functional performance of the pavement is concerned with pavement performance from the point of view of the road users. as characterized by such factors as cracking. Most pavement design concepts in general use. It is clear that the cracks will occur if the pavement is over stressed. PRESENT SERVICEABILITY RATING Psycho Physical Scale Psycho – Physics is concerned with the determination of quantitative relationships between physical stimuli and corresponding psychological or sensory events. undulations. raters are assumed to be inter changeable. 2 and 3 adopted by different agencies) and raters assign appropriate number to each stimulus in time with these cues. The following psychological model is the basis for the subjective determination of pavement serviceability: Serviceability is a discriminate attribute of the highway pavements and raters are capable of making direct quantitative judgement of the amount of this attribute associated with any pavement section. Rating scale methods are most popular psychometric scaling procedures that depend on human judgement. Each rater’s judgement is considered to be direct repeat of the level of serviceability of any pavement on a linear subjective continuum of this attribute. An example being the AASHO road test scale typically consisting of sequence of numbers defined by definition or cues (as given in Table 1. Different organisations have developed their own scale for the use in Present Serviceability Rating procedure. percieved frequency of vibration or subjective weight. frequency of vibration or weight in kilograms. It is implicitly assumed that the scale value estimate may be obtained from the replications by an individual. A numerical rating scale. The origin and units in which the judgements are expressed may be arbitary but they must remain constant. in the form of an externally communicated judgment by an observer. Some variability in judgement with respect to serviceability of any pavement may occur as in the case with any measurement procedure. or from judgements by a number of raters. Psychometric Scaling Procedures Several methods of rating scales have been developed and widely used. That is. It is not possible to measure directly quantities on the response continuum because these may only be estimated by observing an external verbal or symbolic response of an observer. It is from these judgements that evidence concerning that the response continuum must be derived. that is. but they are all essentially alike in that they require the assignments of the objects by inspection. Rating Procedure Rating Panels: It is obvious that the rating panel members have to be so selected they form the representative cross section of the intelligent road users. either along the unbroken continuum or in ordered categories along the continuum. It is usual to 13 . Corresponding to these physical stimuli are certain sensory experiences or response continuation such as pitch. This variability is treated as random error and the individual estimates may be averaged to provide an estimate of the scale value of serviceability.physical property such as frequency of sound waves. Analysis of Rating Data After collecting the data on each selected stretch the data sheets are collected from the raters.indicate highway engineers and reaserch personnel in addition to ordinary highway users.05 to 0. formation of panel size and number of panels. The most probable rating is the average of ratings of all rating panels taken together for each test stretch.0 3 12 8 5 4 3 2 2 The optimum size of rating panel for any combination of E and P can be obtained from the above table. Panel Size The difference between overall rating and the panel rating would gradually diminish with increase in number of members in the panel. 14 . After the subjects are trained.9 3 1.10) over a range of permissible errors ( 0. visually observing the pavement surface condition including the degree of deterioration of surface based on undulations / unevenness.4 17 0. The rating values given by the individual raters is termed as IPSR. n for P= 31 0. the subjects are to be taken in test vehicle driven at a standard uniform speed of 30 km along the test stretches and are trained to assess the present serviceability rating value according to comfort condition. patching. For the rating by riding technique. for assessing the pavement surface by both visual and riding rating techniques. Orientation of Rating Panels An initial orientation program is to be conducted for the raters or the subjects.6 8 0.10 21 0. the raters are asked to evaluate the pavements of selected stretches by both visual and riding rating techniques.3 No of raters. The panel sizes can therefore be so fixed as to ensure any stipulated degree of accuracy for the ratings. The mean value of a panel is termed as PSR. The subjects are to be trained to rate the pavement surface of the typical road stretches by walking along the road.As pointed out by Guilford and Huchinson several systematic errors must be removed from the raw judgements.7 6 0. cracking.05 P = 0. by limiting the value of maximum rating error.8 4 0.0) as fallows Permissible Error E 0. rutting. and other surface distress. The data collected from the test stretches are to be mathematically analysed to get the PSR values. Nakamura and Michael have given the number of raters required to estimate the overall rating for two probability levels (0. to get the true rating values of the pavement.3 to 1.5 11 0. unevenness index values obtained from different mechanical instrument or slope variance and rut depth Extent of surface distress is in the form of cracking and patching etc. With these parameters and assumptions the mathematical models were developed both for flexible and rigid pavements. SV = Average slope variance of left and right wheel paths RD = Average rut depth in wheel path in inches C = Cracked area of pavement in Sq.8 log ( 1+ SV ) – 0. ft of pavement sections Similar studies were conducted by different other Highway agencies like Minnesota and Virginia State Highways Departments of the USA. The ground parameters considered are : change in pavement profile. To develop the mathematical models. which could predict the PSR values. But the Materials Division of the Washington Department of Highway has developed a different type of mathematical model which is in form : R R = GR x G D Where R R = Final Rating GR = Ride Rating = 100 – (10 x ride score) GD = Defect Rating = 100 – (Defects values for pavement defects) 15 . mathematical models were developed correlating the PSR values as obtained by the Rating Panel. both longitudinal and transverse i.09 C+ P Where.38 RD2 – 0.01 ( C + P ) 1/2 For Rigid Pavements PSI = 5. and the physical measurements of various ground parameters affecting the pavement serviceability ratings in the opinion of Rating Panel members.03 – 1.SERVICEABILITY MODELS To obviate the necessity of frequent service rating sessions and to enable smaller test sections to be assessed with reasonable accuracy.41 – 1. Carey and Irick established five fundamental assumption which can be refered in the literature.. obtained from panel ratings with good accuracy in terms of Present Serviceability Index (PSI).91 log ( 1+ SV) – 1.e. The PSI equations developed are in the form : For flexible pavement: PSI = 5. ft / 1000 sq. IRC. World Bank Publication. IRC. In India also the PSI models were developed by CRRI. New Delhi. 5. HRB. Mc Graw Hill Company. V. 16 . Indian Roads Congress.479 – 3. m / 100 Sq. Patterson. “ Surface Unevenness of Highway Pavements” .m) REFERENCES 1. Washington D. 1964. “ Road Conditions and Traffic Safety” MIR Publications. HMSO.2T R = Roughness (U I) inches / mile T = Twice average surface texture depth in hundredths of an inch. Baltimore. 3.In Australia. G.315 – 3. The Johns Hopkins University Press..570 log R – 0. Indian Roads Congress. Indian Roads Congress.. 4. 1978. Pitters and Head developed a model which is in the form: PSI = 14. Highway Research Board. 2. Huchinson.943 log R By considering both roughness and surface distress: PSI = 12. Appropriate Serviceability indices for pavements under Indian conditions which are in the form by considering Roughness ( U I ) alone PSI = 13. Highway Research Record. 10. Babkov. Moscow.. “ Principles of Subjective Rating Scale Construction” . “ The Design and Performance of Road Pavements” TRRL. London.. 8.184 – 2. Special Publication – 11. Hand Book of Quality Control for Construction of Roads and Runways”. 1977. No 46. Special Publications 16. State of the Art : Pavement Slipperiness and Skid Resistance. Mc Graw Hill Book Co. HRB Bull 250.F. Croney. Haas and Hudson “ Pavement Management System”. “ The Pavement Servicebility Performance Concept”. and Irick D. “ Road Deterioration and Maintenance Effects Models for Planning and Management” .0205 D.F.N. 1960.C.327 log RC Where RC = Corrected roughness (Unevenness) = R. B. Carrey W. IRC Special Report. 6. Ralph Haas and W. 7. John Wiley and sons. New York. 9. “ Pavement Management System”. Where R = Roughness ( U I) obtained by Bump Integrator at 30 kmph in cm/km D = Surface distress ( cracking and patching area in Sq. Ronald Hudson. “ Principles of Pavement Design” Second Edition. Yoder and Witczak. Proceedings of the International Conference on Roads and Transport Problems”. “ Role of Road Roughness in Vehicle Ride”. Tata Mc Graw Hill Publishing Company. No 836. Washington D. Road Research Special Report. CRRI. Painter L. 1980. M.G. New Delhi.C. and Sayers. All India Serviceability Rating Study for Highway Pavements”. 1962. New Delhi. C.. 1977. TRR.11. 13. 17 . “ An Alternative Analysis of Present Serviceability Index”. 12. Michigan. Gillespie... T.J. No 2. TRB. First International Conference on Structural Design of Asphaltic Pavements. 14. 1981.E. Krishnamurthy and Justo.D. “ Applications of Psycho – physical method for evaluation of riding quality of road pavements”..
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