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Talks about pavement engineering

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Summer Training Siddharth Srivastava A2315813131(1)Siddharth Srivastava

TRANSPORTATION_ENGINEERING_M5.pdfBASWESHWAR JIRWANKAR

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BBM PPT By HchakravartiHimanshu Chakravarti

ShibShib Sundar Banerjee

Design of Flexible Pavements 1 Amresh Kumar.pptxChandan Srivastava

- 1. BITSPilani Hyderabad Campus Structural Evaluation of Flexible Pavements
- 2. BITS Pilani, Hyderabad Campus I take this opportunity to sincerely thank the IRC, MoRT&H, BIS, CRRI, NHAI, PWDs, R&B, FHWA, NHI, ASTM, AASHTO, NCHRP, Shell, BITS Pilani, Contractors, Consultants, Researchers, my Teachers, my colleagues, my Alma mater, and my students. The contents of this presentation is prepared, directly or indirectly with the help of these resources, and only for the purpose of exchange of knowledge. Acknowledgements
- 3. BITS Pilani, Hyderabad Campus Flexible Pavement Layers
- 4. BITS Pilani, Hyderabad Campus Rutting in the Bituminous Layer Rutting https://civilblog.org/2015/09/18/10-different-types-of-failures-of-flexible-pavement/
- 5. BITS Pilani, Hyderabad Campus Bottom up Cracking https://commons.wikimedia.org/wiki/File:A sphalt_deterioration.jpg Bottom up Cracking
- 6. BITS Pilani, Hyderabad Campus Top-down Cracking Top-down Cracking Top-down Cracking Top-down Cracking
- 7. BITS Pilani, Hyderabad Campus Raveling Ravelling
- 8. BITS Pilani, Hyderabad Campus Pot Hole IRC:116-Specification for Readymade Bituminous Pothole Patching Mix Using Cutback Bitumen https://civilblog.org/2015/09/18/10-different-types-of-failures-of-flexible-pavement/
- 9. BITS Pilani, Hyderabad Campus Flexible Pavement Distresses Slippage Cracking Bitumen Bleeding Milled Surface
- 10. BITS Pilani, Hyderabad Campus Pavement Engineer Materials Engineering Chemistry Mechanical Engineering
- 11. BITS Pilani, Hyderabad Campus Types of Maintenance IRC: 82-2015 • Routine Maintenance Filling of pot holes • Preventive Maintenance To extend the functional life and delay rehabilitation • Periodic Maintenance Application of Renewal Coat
- 12. BITS Pilani, Hyderabad Campus All pavements deteriorate with time. Depending on the initial condition, traffic loading, and climatic conditions. It is necessary to evaluate the functional and structural condition of the pavement periodically. Need for maintenance and rehabilitation can be assessed based on the evaluation study. PavementEvaluation
- 13. BITS Pilani, Hyderabad Campus Evaluation of Pavement Performance Functional Performance: The ability of pavement to provide comfortable, safe, economical riding quality to the road users. [Pavement Condition Index (PCI), roughness, skid resistance] Structural Performance: Related to the load carrying capacity of the pavement. [Pavement response to load application] PavementEvaluation
- 14. BITS Pilani, Hyderabad Campus Structural evaluation of pavements can be either destructive or Non-destructive. Destructive evaluation: the pavement is cut open to find the in-situ condition, and the samples are collected for testing in the laboratory. Non-destructive evaluation: Load is applied on the pavement for measuring the structural response. Structural Evaluation
- 15. BITS Pilani, Hyderabad Campus Destructive Evaluation
- 16. BITS Pilani, Hyderabad Campus The general approach of structural evaluation is: 1. Application of specified load in a specified manner. 2. Measuring the surface deflection. 3. Back calculate the material properties from the measured deflections to the applied loads. GeneralApproach
- 17. BITS Pilani, Hyderabad Campus NDT Evaluation Static Load Testing of Pavements Example : Plate Load Test Plate Load Test
- 18. BITS Pilani, Hyderabad Campus Plate Load Test
- 19. BITS Pilani, Hyderabad Campus •The NDT load applications can be in different modes i. Static ii. Slow moving or Creep iii. Vibratory iv. Impulse NDT Evaluation
- 20. BITS Pilani, Hyderabad Campus Benkelman beam apparatus - Static/Creep Loading Benkelman beam is an apparatus used for measuring the surface deflection of pavement subjected to a standard truck load NDT Evaluation
- 21. BITS Pilani, Hyderabad Campus Western American State Highway Officials (WASHO) Method – Deflection is noted as the wheel load approaches the point. Benkelman Beam Evaluation of Pavements Maximum Deflection noted Deflection = 0
- 22. BITS Pilani, Hyderabad Campus • Canadian Good Roads Association (CGRA) method– Rebound deflection measured as the load is removed from a point. Benkelman Beam Evaluation of Pavements Deflection = 0 Maximum Initial Deflection
- 23. BITS Pilani, Hyderabad Campus • Single maximum rebound deflection is measured. • Structural response is measured under static or creep load and doesn’t representative a fast moving truck. • Structural capacity of the pavement is assessed based on a single deflection measurement. Benkelman Beam Evaluation
- 24. BITS Pilani, Hyderabad Campus • Determining the structural deficiency and design of overlay was a Research Project. • The test Sections in different parts of the country were evaluated by different educational institutions • The project was coordinated by CSIR-CRRI and reported as IRC:81-1997. R-6 Research Project of MoRTH
- 25. BITS Pilani, Hyderabad Campus Outcomes from the project were: 1. Limiting the Deflection value 2. N = k1(1/Initial Deflection)K2 3. Effectiveness of overlay thickness in reducing deflection 4. Equivalence of materials (in terms of BM) 5. Corrections to be applied to measured surface deflections 6. The information was summarised to arrive at an overlay thickness chart R-6 Research Project of MoRTH
- 26. BITS Pilani, Hyderabad Campus Overlay Design IRC:81-1997
- 27. BITS Pilani, Hyderabad Campus Pavements that do not have adequate structural strength to carry the projected future traffic will have to be strengthened by providing additional layer/s Overlay Overlay Existing Pavement Sub-grade
- 28. BITS Pilani, Hyderabad Campus • Guidelines for Strengthening of Flexible Road Pavements using Benkelman Beam Deflection T echnique • First version in 1981. First revision in 1997 • MORTH research scheme R – 6 entitled “Development of Methods such as Benkelman beam deflection method for evaluation of structural capacity of existing pavements and also for strengthening of any weak pavement” Indian Roads Congress Overlay Design
- 29. BITS Pilani, Hyderabad Campus • For evaluation of the strengthening requirement of existing flexible road pavements using Benkelman beam technique • Pavement performance is closely related to the elastic deflection of pavement under wheel loads • Elastic deflection under standard loading conditions depends upon subgrade soil type, moisture condition, degree of compaction, the thickness and quality of the pavement courses, drainage conditions, pavement surface temperature, etc. IRC:81 Scope and Principle
- 30. BITS Pilani, Hyderabad Campus Benkelman beam is a simple apparatus commonly used for measuring the surface deflection of a pavement under standard loading conditions Benkelman Beam 2.44 m 1.22 m
- 31. BITS Pilani, Hyderabad Campus Slender beam of length 3.66m hinged at 2.44m from the pivot Observed deflection Rebound deflection Benkelman Beam
- 32. BITS Pilani, Hyderabad Campus • Static/Creep Loading using Benkelman beam apparatus • Benkelman beam is used for measuring the pavement surface deflection subjected to a standard truck load Benkelman Beam
- 33. BITS Pilani, Hyderabad Campus Length of beam from Hinge to Probe = 2.44 m Length of beam from Hinge to Dial = 1.22 m Distance from Hinge to front legs = 0.25 m Distance from Hinge to rear legs = 1.66 m Lateral spacing of front support legs = 0.33 m CGRA Method – Beam Details
- 34. BITS Pilani, Hyderabad Campus 5 tonne truck is recommended to apply load Rear axle = 8170 kg (equally distributed over the two dual wheel sets Spacing between tyres = 30 – 40 mm Tyres – 10 X 20, 12 ply Tyre Pressure = 5.6 kg/cm2 (0.56 MPa) CGRA Method – Loading Details
- 35. BITS Pilani, Hyderabad Campus Pressure measuring gauge Thermometer (0-100 C) Mandrel for making 4.5 cm deep hole in the pavement for temperature measurement Deflection Measurement – Other Accessories
- 36. BITS Pilani, Hyderabad Campus • Mark a Point on the pavement at 60 cm from pavement edge for single lane roads and at 90 cm from pavement edge for wider lanes • For divided four lane highways, the point should be selected at 1.5 m from edge • Place the outer dual wheel set at the location (centred) • Insert probe of the beam between the dual wheels. • Probe will be on the selected point locking pin removed. • Support frame levelled. Deflection Measurement – Procedure
- 37. BITS Pilani, Hyderabad Campus Deflection Measurement – Procedure x Direction of traffic Pavement Shoulder 0.9 m for a two lane 1.5 m for a divided 0.6 m for a single lane
- 38. BITS Pilani, Hyderabad Campus • Beam plunger brought in contact with the stem of the dial gauge. Initial reading in dial gauge noted • Truck driven forward to a distance of 2.7 m. Observe intermediate reading in the dial gauge • Move the truck forward a further distance of 9 m and note the final dial gauge reading • Dial gauge readings are to be noted when either the rate of deformation or rate of recovery is less than 0.05 mm BBD Procedure
- 39. BITS Pilani, Hyderabad Campus Benkelman Beam Placement Placement of Benkelman Beam to measure Pavement Deflection
- 40. BITS Pilani, Hyderabad Campus • Measure the temperature every hour by inserting the thermometer in the hole made in the bituminous surface after filling the hole with glycerol • Tyre pressure is checked at two to three hours interval Deflection Measurement – Procedure
- 41. BITS Pilani, Hyderabad Campus Benkelman Beam – Deflection Measurement Initial Reading Intermediate Reading 2.7 m 9 m Final Reading
- 42. BITS Pilani, Hyderabad Campus • Computation of Rebound Deflection for the Point • Subtract Final dial reading from Intermediate dia reading. Subtract Intermediate Dial reading from Initial reading. • If difference between final and intermediate dial readings is less than 0.025 mm, the actual pavement rebound deflection is twice the difference • If the difference is more than 0.025 mm compute the rebound deflection as follows Benkelman beam – Deflection Measurement
- 43. BITS Pilani, Hyderabad Campus Pavement rebound deflection = 2 (Final – Initial readings) + 2.91 X 2 (difference between final and intermediate readings) Benkelman beam – Deflection Measurement
- 44. BITS Pilani, Hyderabad Campus Selection of Homogenous Sections Benkelman beam Deflection Survey Classification Pavement Condition Good No Cracking, rutting <10 mm Fair No Cracking or cracking confined to a crack in the wheel track, rutting between 10 and 20 mm Poor Extensive cracking and rutting>20mm Sections with cracking exceeding 20 per cent shall be treated as failed
- 45. BITS Pilani, Hyderabad Campus Selection of Homogenous Sections • On the basis of surface condition survey, the total stretch is divided into uniform sections • Length of each section is kept at a minimum of 1 km Benkelman beam Deflection Survey
- 46. BITS Pilani, Hyderabad Campus Deflection Measurements • For each uniform section of road, minimum of 10 points should be selected at equal distance in each lane of traffic • Points to be selected along outer wheel paths • Interval between points should not be more than 50 m • On roads with more than one lane, the points on the adjacent lanes can be staggered Benkelman beam Deflection Survey
- 47. BITS Pilani, Hyderabad Campus • In case of extreme deflection values, additional deflection measurements to be made • If the highest or lowest deflections differ from the mean by more than one-third of mean then extra deflection measurements should be made at 25 m on either side of the point • Measured Deflections have to be corrected to correspond to a standard pavement temperature • Measured deflections also have to be corrected to correspond to worst condition Benkelman beam Deflection Survey
- 48. BITS Pilani, Hyderabad Campus 0.01 mm correction for each degree variation from 35 C If measured deflection at 38 C = 0.8 mm, then the corrected deflection = 0.8 – 3 X 0.01 = 0.77 mmfor Seasonal Variation Weakest Condition soon after monsoon. Deflection will vary with variation in subgrade strength which is affected by the variation in moisture content with season Benkelman beam Deflection Survey
- 49. BITS Pilani, Hyderabad Campus •Correction for Seasonal Variation Field moisture content of the subgrade soil sample has to be determined during the deflection survey Soil type (classification) also has to be determined Correction factors are available for different types of subgrade soils, different rainfall conditions and different field moisture contents 3-categories of soils – clayey with low plasticity (PI < 15), clayey with high plasticity (PI > 15) and sandy/gravelly Benkelman beam Deflection Survey
- 50. BITS Pilani, Hyderabad Campus Collection of Soil Sample for Field Moisture
- 51. BITS Pilani, Hyderabad Campus Sandy/Gravelly Soil for Low Rainfall Area
- 52. BITS Pilani, Hyderabad Campus Sandy/Gravelly Soil for High Rainfall Area
- 53. BITS Pilani, Hyderabad Campus Clayey Subgrade for Low Rainfall Area (PI<15)
- 54. BITS Pilani, Hyderabad Campus Clayey Subgrade for High Rainfall Area (PI<15)
- 55. BITS Pilani, Hyderabad Campus Clayey Subgrade for Low Rainfall Area (PI>15)
- 56. BITS Pilani, Hyderabad Campus length of the uniform stretch selected Characteristic deflection, Dc = Mean (X) of all the measured deflections + k * standard deviation () of measured deflections For major arterial roads like NH & SH Dc = X + 2 For all other roads Dc = X + Estimation of Characteristic Deflection
- 57. BITS Pilani, Hyderabad Campus Design of Overlay involves the following steps 1. Selection of Design period 2. Projection of Commercial traffic for the design period 3. Estimation cumulative standard axle load repetitions for the design period 4. Selection of characteristic rebound deflection for the existing pavement on the basis of rebound deflection survey conducted using Benkelman beam
- 58. BITS Pilani, Hyderabad Campus Traffic : A = P (1 + r)n+10 A = commercial vehicles per day in the year of completion of construction P = commercial vehicles per day at last count r = Annual rate of increase of commercial vehicles (7.5%) n = Number of years between the last count and the year of completion of overlay construction Estimation of Traffic for design period
- 59. BITS Pilani, Hyderabad Campus = 365 x A [(1+ r)x – 1] x F ----------------------------- r Where N = cumulative number of standard axles to be catered for during the design period A = Initial traffic in the year of completion of construction modified to account for the lane distribution r = Annual rate of growth of commercial vehicles (7.5%) x = X= Design life, years (10 for major roads, 5 for less important roads) F = Vehicle Damage Factor Estimation of Traffic for design period
- 60. BITS Pilani, Hyderabad Campus Single Lane (3.75m width) – Total two-way commercial traffic multiplied by two 2-lane single carriageway (2-way traffic) – 75% of total two- way traffic 4-lane single carriageway – 40% of total two way commercial traffic Dual carriageway – 75 % of commercial volume in each direction for dual 2-lane carriageway For each additional lane, reduce the distribution factor by 20% Estimation of Traffic for design period
- 61. BITS Pilani, Hyderabad Campus To be obtained from axle load survey Indicative VDF Values are 0-150 cvpd Initial traffic – 1.5 (Rolling/Plain) 0.5 (Hilly) 150-1500 cvpd – 3.5 (Rolling/Plain) 1.5 (Hilly) > 1500 cvpd – 4.5 (Rolling/Plain) 2.5 (Hilly) Estimation of Traffic for design period
- 62. BITS Pilani, Hyderabad Campus • Thickness charts give the overlay requirement in terms of Bituminous Macadam construction • BM can be converted into other materials using equivalency factors BM = 1.5 WBM / WMM 1 BM = 0.7 DBM / BC • Minimum thickness of overlay = 50 mm BM with an additional surfacing course of 50 mm DBM or 40 mm BC Overlay Design
- 63. BITS Pilani, Hyderabad Campus Overlay Design Chart
- 64. BITS Pilani, Hyderabad Campus A and B are for two different pavement systems having the same maximum deflection but different deflection bowl shapes Maximum deflection alone does not give an indication of the condition of different components of the pavement Benkelman Beam Evaluation of Pavements A B
- 65. BITSPilani Hyderabad Campus Precautions during Overlay Construction
- 66. BITS Pilani, Hyderabad Campus Wayne Jones, P.E. – Asphalt Institute
- 67. Failure of Pavement Due to Poor Drainage
- 68. Schematic Representation of Machineries Required for Bituminous Paving Work
- 69. BITS Pilani, Hyderabad Campus IS:73-2013 Reaffirmed 2018
- 70. BITS Pilani, Hyderabad Campus BTDC
- 71. BITS Pilani, Hyderabad Campus Aging of Bitumen From production toend of bituminous surface life Shell Bitumen Hand Book- Redrawn Aging during mixing Aging during storage, transport and application Aging after 8 years Service Aging Index Age, Years 0 years 8 years
- 72. BITSPilani Hyderabad Campus Falling Weight Deflectometer IRC: 115-2014
- 73. BITS Pilani, Hyderabad Campus Structural Evaluation- General Structural Evaluation of Pavements involves the application of standard load to the pavement and measuring its responses in terms of stresses, strains and deflections. Benkleman Beam is used as the earlier equipment for structural evaluation. A static load is applied on the pavement surface and rebound deflections are measured at one or more locations. Measurement of static load does not simulate the loading conditions produced by moving conditions.
- 74. BITS Pilani, Hyderabad Campus Benkleman Beam will under estimate the strength of DBM and BC. It is labor intensive and time consuming method and test results are mostly affected by moving traffic on the adjacent lanes. It is unsafe for heavy traffic conditions (safety) . Repeatability of test results is always a concern. This method does not predict the properties of the individual layers which is necessary for comprehensive evaluation of pavement. BenklemanBeam–Limitations
- 75. BITS Pilani, Hyderabad Campus PrincipleofFWD
- 76. BITS Pilani, Hyderabad Campus PrincipleofFWD
- 77. BITS Pilani, Hyderabad Campus PrincipleofFWD
- 78. BITS Pilani, Hyderabad Campus What is FWD? Falling Weight Deflectometer (FWD) is the device that measure the deflection response of structures due to a load generated by the arrest of a falling mass. Data collected by FWD is generally used to calculate the stiffness or stiffness-related parameters of pavements or pavement layers. FallingWeight Deflectometer
- 79. BITS Pilani, Hyderabad Campus Factors Influencing the performance of flexible pavements such as thickness, subgrade strength, quality of each layer, pavement surface temperature. When a moving wheel load passes over the pavement it produces impulses. Normal stresses at a location in the pavement will increase from zero to peak value as the moving wheel load approaches the location. The time taken for the stress pulse to vary from zero to peak value is termed as the rise of pulse. The time period during which the magnitude of stress pulse varies from 'zero-to-peak-to-zero' is the pulse duration. FallingWeight Deflectometer
- 80. BITS Pilani, Hyderabad Campus Peak load and the corresponding pavement responses are of interest for pavement evaluation. The resulting load-deflection data can be interpreted through appropriate analytical techniques, such as back calculation technique, to estimate the elastic moduli of the pavement layers. The computed moduli are, in turn, used for (i) The strength evaluation of different layers of in-service pavements (ii) The estimation of the remaining life of in-service pavement (iii) Determination of strengthening requirement, if any and (iv) Evaluation of different rehabilitation alternatives (overlay, recycling, partial reconstruction, etc.) FallingWeight Deflectometer
- 81. BITS Pilani, Hyderabad Campus FWD is an impulse loading device. The load is applied by falling mass over a circular loading plate and the deflected shape of the pavement surface i.e. deflection bowl is measured. Deflections are measured by displacement sensors placed under the load and also at a distance of 0, 300, 600, 900, 1200, 1500 and 1800 mm. Different magnitude of impulse load can be obtained by selection of a suitable mass and an appropriate height of fall. Drop 100 to 600 mm can be used. PrincipleofFWD(IRC115-2014)
- 82. BITS Pilani, Hyderabad Campus Typical Falling Weight Deflectometer (FWD) include a circular loading plate of 300 or 450 mm diameter. In general 300 mm diameter load plate is recommended. A rubber pad of 5 mm minimum thickness should be glued to the bottom of the loading plate for uniform distribution of load. Alternatively, segmented loading plates (with two to four segments) can be used for better load distribution. Generaldetails ofFWD
- 83. BITS Pilani, Hyderabad Campus The measured deflection are normalized for a standard target load of 40 kN. Can be increased to produce at least 10 µm at 1200 mm distance. Measured deflections can be normalized for 40 kN (linear) (eg 0.8*40/45 if the measured deflection is 0.8 mm at 45 kN). Calibration of FWD is essential for getting accurate and reproducible results. 15 to 50 ms loading time. 6 to 9 deflection sensors (1 µm resolution or 2% of the load cell reading). Different sensor configurations. Generaldetails ofFWD
- 84. BITS Pilani, Hyderabad Campus A falling mass in the range of 50 to 350 kg is dropped from a height of fall in the range of 100 to 600 mm to produce load pulses of desired peak load and duration. Heavier models use falling mass in the range of 200 to 700 kg. The target peak load to be applied on bituminous pavements is 40 kN (+/- 4 kN), which corresponds to the load on one dual wheel set of a 80 kN standard axle load. The target peak load can be decreased suitably if the peak maximum (central) deflection measured with 40 kN load exceeds the measuring capacity of the deflection transducer. Generaldetails ofFWD
- 85. BITS Pilani, Hyderabad Campus Typical geophone position configurations (number and radial distances measured from center of load plate) commonly used for flexible pavement evaluation are : (i) 7 sensors at 0, 300, 600, 900, 1200, 1500 and 1800 mm radial distances. (ii) 7 sensors at 0, 200, 300, 450, 600, 900, 1500 mm radial distances. (iii) 6 sensors at 0, 300, 600, 900, 1200 and 1500 mm radial distances and (iv) 6 sensors at 0, 200, 300, 600, 900, 1200 mm radial distances. Displacement Sensors offsets for FWD
- 86. BITS Pilani, Hyderabad Campus Targetloadsandacceptable ranges
- 87. BITS Pilani, Hyderabad Campus Static calibration • The load cells used in the FWD should be calibrated in a standard laboratory and the readings of the load cells should be matched to those of the reference load cell. • The readings of the FWD load cells should be accurate to 2 percent of the reference load cell readings. • The date of calibration of the load cell should not be earlier than 365 days from the date of structural evaluation of pavements using FWD. Calibration ofFWD
- 88. BITS Pilani, Hyderabad Campus Load repeatability • For this test, FWD measurements should be carried out on a level bituminous pavement surface, which does not have any cracking. • The range of load applied should generate peak central deflections in the range of 250 m to 600 m. • The standard deviation of the peak load in the load repeatability test estimated from a minimum of twelve load drops should be less than 5 percent of the mean value of peak load. • Load repeatability may be checked before using the FWD for any major investigation. Calibration ofFWD
- 89. BITS Pilani, Hyderabad Campus Absolute calibration of deflection transducers • Dismounted deflection transducers should be calibrated in a laboratory (±2 percent of the reference deflections). • The calibration of geophones should be done every year. • Check for deflection repeatability. • The standard deviation should be ±5% of the mean value wrt the normalized deflections. • The deflections produced in this test should 250 µm to 600 µm. • Difference between max and min deflections should be ±4 µm. Calibration of FWD
- 90. BITS Pilani, Hyderabad Campus Construction history, performance data, etc. should be collected. Pavement Condition Survey – Rutting and cracking. Data recorded for 50 m X 3.5 m blocks. Uniform sections identified (Good, Fair, Poor) as per guidelines given. FWDEvaluation
- 91. BITS Pilani, Hyderabad Campus CriteriaforClassification of PavementSections
- 92. BITS Pilani, Hyderabad Campus Guidelines forSelection of Deflection Measurement
- 93. BITS Pilani, Hyderabad Campus The length of uniform section is 1.0 km. The actual spacing can be obtained by multiplying the spacing by the length of uniform section. Deflections may be measured along the hard shoulders if the same are proposed to form part of the new lane in case of widening projects. Guidelines forSelection of Deflection Measurement
- 94. BITS Pilani, Hyderabad Campus Positions of wheel paths must be identified by observing the surface condition of the road. If the same cannot be done, the following guidelines can be used for identifying the outermost wheel path. Outer wheel paths of outer lanes :- i) For single-lane two-way carriageway :- at 0.6 m from the outer edge of the outer lane. ii) For two-lane two-way carriageway and for multi-lane single carriageway :- at 1.0 m from the outer edge of outer lane. iii) For divided carriageways with two or more lanes in each direction :- 0.75 m from the outer edge of outer lane. Positions ofwheelpaths
- 95. BITS Pilani, Hyderabad Campus Outer wheel paths of inner lanes :- i) For multi-lane single carriageway :- at 4.0 m from the outer edge of outer lane. ii) For divided carriageways with two lanes in each direction 4.2 m from the outer edge of outer lane. iii) For divided carriageways with three lanes in each direction 4.2 m from the outer edge of outer lane for central lane and at 5.2 m from the outer edge of outer lane for the lane adjacent to median. Positions ofwheelpaths
- 96. BITS Pilani, Hyderabad Campus The following data should be recorded for each test point. 1. Identify the Section 2. Lane Position (outer lane, inner lane, etc.) 3. Transverse position of test point 4. Measurement spacing 5. Time of test 6. Air temperature and pavement temperature at 40 mm depth 7. Drop number 8. Peak values of load and deflections for each drop 9. Time history of load and deflections for one of the test points of each road section 10. Number of sensors and the Load plate diameter FWD-Data Collection
- 97. BITS Pilani, Hyderabad Campus 1. Mark the test point. 2. Centre the load plate over the test point. 3. Lower the loading plate onto the pavement. 4. Lower the frame holding the geophones. 5. Raise the mass to a pre-determined height for a target load of 40 kN. 6. Drop one seating load, and do not record. 7. Raise the mass and drop it for recording the readings. 8. Repeat step 7 for two more times. Stepsformeasuring deflection ata testpoint
- 98. BITS Pilani, Hyderabad Campus 9. During steps 7 and 8, if the deflections measured are too large or too small, the test may be repeated by changing the peak load. 10. Raise the geophone frame and load plate and move to the next test Location. 11. Record air and pavement temperatures at half hourly interval. 12. Record pavement surface temperature (optional). 13. Deflection measurements should not be made when the pavement temperature is more than 45 °C. Guidelines given in Clause 6.4.3 may be followed for deflection measurement in colder areas and areas of altitude greater than 1000 m. Stepsformeasuring deflection ata testpoint
- 99. BITS Pilani, Hyderabad Campus Pavement layer thicknesses are essential inputs to the process of back calculation of layer moduli and, in turn, to the estimation of remaining life and overlay requirements of the in- service pavement. Layer thicknesses can be obtained from historical data, by coring bound layers and/or by excavating test pits and/or through the non-destructive technique of Ground Penetrating Radar (GPR) survey. It is recommended that 0.6 m x 0.6 m test pits be excavated at 1.0 km interval or at suitable larger interval where other records suggest uniformity of pavement composition in such larger sections. Determination ofPavement Layer Thicknesses
- 100. BITS Pilani, Hyderabad Campus Dynamic Cone Penetrometer (DCP) tests may be conducted on the subgrade layer exposed in the test pits to obtain the Dynamic Cone Penetrometer value for in-situ subgrade. The DCP values obtained with a 60° cone can used to estimate the back calculated modulus value of subgrade layer using equation: DCP = Dynamic Cone Penetrometer value (mm/blow) Dynamic ConePenetrometer (DCP)
- 101. BITS Pilani, Hyderabad Campus Deflections should decrease with distance. Deflection should not be more than the capacity of the sensor. No FWD test when the temperature is more than 45 degree Celsius. Collect layer thickness data. Analysis ofData
- 102. BITS Pilani, Hyderabad Campus Estimation ofsamplesize The following equation can be used for estimating the sample size (n) n = sample size z = normalized normal deviate which can be obtained from standard statistical tables for a selected confidence level CV = coefficient of variation of deflection (standard deviation/mean) expressed as percentage ME = acceptable margin of error (as percentage of mean)
- 103. BITS Pilani, Hyderabad Campus 90% confidence level and 10% acceptable margin of error (ME) recommended. CV of 15, 30 and 45% may be considered for Good, Fair and Poor sections (AASHTO 1993). For a one sided confidence level of 90% for which the standard normal deviate is 1.285 and for 10% ME, the values of n for Good , fair and Poor sections are 4, 15, 33 If the uniform section length is 2.0 km and is fair, 15 observations should be made in 2.0 km , ie at a spacing of 2000/15 = 133 m. Measurement scheme given for different carriageways. Estimation ofsamplesize
- 104. BITS Pilani, Hyderabad Campus A statistical technique popularly used for identification of homogeneous sections is the "Cumulative Difference" approach. The series of cumulative differences (zj for the measured sequence of a given variable 'x' (SCI, subgrade strength, etc.) can be obtained using the following expression. Identification ofhomogeneous sections
- 105. BITS Pilani, Hyderabad Campus Back Calculation is the process of selection and adjustment of layer moduli using any technique (iteration, database searching, closed-form solution, optimization) so that the deflections computed using the adjusted layer moduli are close to the measured deflections. Backcalculation
- 106. BITS Pilani, Hyderabad Campus BackCalculation InANutshell Most back calculation programs, including those used to generate the back calculated modulus data in the LTPP-computed parameter tables, involve the use of numerical integration subroutines that are capable of calculating FWD pavement deflections and other parameters, given the stiffness's (or moduli) of the various pavement layers and their thicknesses, etc. If all assumptions are correct, meaning each layer is an elastic layer, is isotropic and homogeneous, and all other boundary conditions are correct, then it is possible to iterate various combinations of moduli until there is a virtually perfect match between measured and theoretical FWD deflections. In this manner, a solution to the problem of deriving moduli from deflections, instead of the other way around, is obtained.
- 107. BITS Pilani, Hyderabad Campus Back calculate using KGPBACK. Suitable moduli ranges are to be assigned. Subgrade 20 to 100 MPa or 5 to 20 times CBR (in-situ CBR estimated from DCP) OR from deflections measured at 1200 mm, 1500 mm and 1800 mm. Granular 100 to 500 MPa. Thick bituminous layers without much cracking (750 to 3000 MPa). Distressed Bituminous layers (fair to Poor) 400 MPa to 1500 MPa. Backcalculation using KGPBACK
- 108. BITS Pilani, Hyderabad Campus IRC:37 performance criteria for design of bituminous pavements can be used. Rutting along wheel paths and cracking of bituminous layer are the main distresses considered. Performance Criteria
- 109. BITS Pilani, Hyderabad Campus Mechanistic Parameters controlling Pavement Performance / distresses
- 110. BITS Pilani, Hyderabad Campus Indian Roads Congress (IRC:37-2001) adopts Linear Elastic Layered Theory for analysis of flexible pavements. Recommends that the pavements be modeled as Three – Layer Systems with Bituminous surface, granular base and subgrade. Interfaces between layers are considered to be rough The top two layers are assumed to be infinite in horizontal direction while the subgrade in semi-infinite. Computation ofStrains
- 111. BITS Pilani, Hyderabad Campus Computation ofStrains Inputs required for analysis Thicknesses of the first two layers Elastic moduli of the three layers Poisson ratio values of the three layers
- 112. BITS Pilani, Hyderabad Campus Loading Considered Standard axle load (80 kN) – One dual wheel set only is considered, tyre pressure 0.56 MPa (80 psi). Computation ofCritical Strains
- 113. BITS Pilani, Hyderabad Campus Rutting Criterion
- 114. BITS Pilani, Hyderabad Campus FatigueCriterion
- 115. BITS Pilani, Hyderabad Campus Correction for Temperature The backcalculated modulus of bituminous layer obtained from deflection survey conducted at a temperature “T2” °C can be corrected to estimate the modulus corresponding to a temperature of "T1" °C using equation. Backcalculation ofLayerModuli 2
- 116. BITS Pilani, Hyderabad Campus CorrectionforTemperature The relationship can be extrapolated up to a temperature range of 20 to 45 °C. Temperature correction need not be applied to backcalculated modulus values of thin bituminous layers (less than 40 mm) and for "poor" sections. In colder areas and areas of altitude greater than 1000 m where the average daily temperature is less than 20 °C for more than 4 months in a year, the standard pavement temperature of 35 °C will not apply.
- 117. BITS Pilani, Hyderabad Campus CorrectionforSeasonal Variation
- 118. BITS Pilani, Hyderabad Campus CorrectionforSeasonal Variation
- 119. BITS Pilani, Hyderabad Campus Computation ofDesign Traffic where, N = cumulative number of standard axles to be catered for in the design in terms of million standard axles, msa A = Initial traffic in the year of completion of construction, in terms of number of Commercial Vehicles Per Day (CVPD) D = Lane distribution factor F = Vehicle Damage Factor (VDF) n = Design life in years r = Annual growth rate of commercial vehicles expressed in decimal (eg : for 5 percent annual growth rate, r = 0.05)
- 120. BITS Pilani, Hyderabad Campus The traffic in the year of completion is estimated using the following formula. A=P(1+r)^X where, P = Number of commercial vehicles as per last count x = Number of years between the last count and the year of completion of construction Computation ofDesign Traffic
- 121. BITS Pilani, Hyderabad Campus i) Single-lane roads (3.75 m width) Traffic tends to be more channelized on single-lane roads than two-lane roads and to allow for this concentration of wheel load repetitions, the design should be based on total number of commercial vehicles in both directions. ii) Two-lane single carriageway roads The design should be based on 50 percent of the total number of commercial vehicles in both directions. If vehicle damage factor in one direction is higher, the design traffic in the direction of higher VDF is recommended. Distribution ofcommercial traffic overthecarriageway
- 122. BITS Pilani, Hyderabad Campus iii) Four-lane single carriageway roads The design should be based on 40 percent of the total number of commercial vehicles in both directions. iv) Dual carriageway roads The design of dual two-lane carriageway roads should be based on 75 percent of the number of standard axles in each direction. For dual three-lane carriageway and dual four-lane carriageway, the distribution factor will be 60 percent and 45 percent respectively. Distribution of commercial traffic over the carriageway
- 123. BITS Pilani, Hyderabad Campus The Vehicle Damage Factor (VDF) is a multiplier for converting the number of commercial vehicles of different axle loads to equivalent number of standard axle load (80 kN) repetitions. It gives the equivalent number of standard axles per commercial vehicle. The vehicle damage factor is arrived at from axle load surveys conducted on typical road sections so as to cover various influencing factors such as traffic mix, type of transportation, type of commodities carried, time of the year, terrain, road condition and degree of enforcement. VehicleDamage Factor(VDF)
- 124. BITS Pilani, Hyderabad Campus AxleLoadSurvey Sample Size for Axle Load Survey
- 125. BITS Pilani, Hyderabad Campus The following equations are used to compute equivalent axle load factors for different axles assembly. Equivalent axleloadfactors
- 126. BITS Pilani, Hyderabad Campus Vehicledamage factor Indicative VDF Values
- 127. BITS Pilani, Hyderabad Campus (i) Measurement of surface deflections of the in-service pavement homogeneous section using FWD. (ii) Normalization of the deflections to correspond to a standard load of 40 kN. (iii) Collection of information about layer type and layer thicknesses. (iv) Backcalculation of pavement layer moduli from the normalized deflections using an appropriate backcalculation software. OVERLAYDESIGN
- 128. BITS Pilani, Hyderabad Campus (v) Adjustment of the bituminous layer modulus (backcalculated) to a standard temperature of 35 C (vi) Adjustment of the subgrade modulus to correspond to post-monsoon condition. (vii)Analysis of the in-service pavement using elastic layer theory with the backcalculated (corrected) moduli and layer thicknesses collected from field as inputs. OVERLAYDESIGN
- 129. BITS Pilani, Hyderabad Campus (vii)This includes computation of critical Strains o Horizontal Tensile Strain at the bottom fiber of bituminous layer. o Vertical Compressive Strain on top of subgrade. The loading configuration and the locations of critical strains considered for analysis will be similar to those adopted in IRC:37-2012. (viii) Estimation of the remaining life of the pavement using the fatigue and rutting performance criteria adopted in IRC:37. The strain values obtained in step vii will be used to estimate the remaining lives from fatigue and rutting consideration. OVERLAYDESIGN
- 130. BITS Pilani, Hyderabad Campus (ix) For design of bituminous overlay, a trial thickness of overlay of an appropriate material has to be selected and the critical strains have to be evaluated. The modulus value of the bituminous overlay material may be selected as per the guidelines given in IRC:37-2012. (x) Design overlay thickness can be selected by trial in such a way that the computed critical strains are less than the permissible limits given by the performance criteria for the design traffic level considered. OVERLAYDESIGN
- 131. BITS Pilani, Hyderabad Campus Available methods differ in terms of (1) Pavement system considered (2) Theory used for the analysis of pavement (3) Backcalculated parameters and (4) Backcalculation technique Backcalculation Methods
- 132. BITS Pilani, Hyderabad Campus Number of commercial backcalculation softwares available. Different models were developed at IIT Kharagpur o Regression o ANN o GA-based o ANN-GA based BACKGA – A GA based model is used currently Backcalculation Models
- 133. BITS Pilani, Hyderabad Campus • FWD pavement evaluation data includes Load applied Load plate radius Surface deflections at different radial distances • This data is used to Back calculate the material properties of different layers in flexible pavements. • Thicknesses of flexible pavement layers also can be back calculated though layer thicknesses are usually taken as inputs for back calculation. Interpretation of FWD data
- 134. BITS Pilani, Hyderabad Campus It is the process of selection and adjustment of layer moduli using any technique (iteration, database searching, closed-form solution, optimization) so that the deflections computed using the adjusted layer moduli are close to the measured deflections. Back calculation
- 135. BITS Pilani, Hyderabad Campus Major Highways- Structural Overlay of Pavements using FWD (in place of BBD Technique) Major Application
- 136. BITS Pilani, Hyderabad Campus • Pavement Evaluation Procedure • Performance Criteria • Back calculation of Inputs to be used in the performance criteria • Estimation of remaining life • Design of overlay Guidelines for an FWD-based Overlay Design Method for India
- 137. BITS Pilani, Hyderabad Campus These guidelines are meant for evaluating the strengthening requirement of existing flexible road pavements using Falling Weight Deflectometer technique. The recommendations are mainly based on the findings of MoRTH Research study (R-81) “Structural evaluation of pavements using Falling Weight Deflectometer” and other relevant information gathered from other sources” IRC:115-2014 ( Formulated by IIT Kharagpur)
- 138. BITS Pilani, Hyderabad Campus (i) Measurement of surface deflections of the in-service pavement homogeneous section using FWD (ii) Normalization of the deflections to correspond to a standard load of 40 kN (iii) Collection of information about layer type and layer thicknesses (iv) Backcalculation of pavement layer moduli from the normalized deflections using an appropriate backcalculation software (eg : E1, E2, E3) OVERLAYDESIGN METHODOLOGY
- 139. BITS Pilani, Hyderabad Campus (v) Adjustment of the bituminous layer modulus (backcalculated) to a standard temperature of 35 C OVERLAYDESIGN METHODOLOGY E (T1) = λ E (T2) Where λ, temperature correction factor =(1-0.238ln(T1))/(1-0.238ln(T2)) Where, E (T1) = backcalculated modulus at temperature T1 E (T2) = backcalculated modulus at temperature T2
- 140. BITS Pilani, Hyderabad Campus (vi) Adjustment of the subgrade modulus to correspond to post-monsoon condition OVERLAYDESIGN METHODOLOGY Seasonal Correction Esub_mon = 28.39 + 0.2888 Esub_win Esub_mon = 21.821+ 0.3641 Esub_sum
- 141. BITS Pilani, Hyderabad Campus (vi) Analysis of the in-service pavement using elastic layer theory with back calculated (corrected) moduli and layer thicknesses collected from field as inputs. (vii) This includes computation of critical Strains (a) Horizontal Tensile Strain at the bottom fiber of bituminous layer and (b) Vertical Compressive Strain on top of subgrade. OVERLAYDESIGN METHODOLOGY h1 h2 E1, 1 E2, 2 E3, 3 et ez Bituminous Granular Subgrade
- 142. BITS Pilani, Hyderabad Campus (viii) Estimation of the remaining life of the pavement using the fatigue and rutting performance criteria adopted in IRC:37. The strain values obtained in step vii will be used to estimate the remaining lives from fatigue and rutting consideration NF = 2.21 * 10-4 (1/et)3.89(1/Eac)0.854 OVERLAYDESIGN METHODOLOGY NF = Cumulative std. Axle load repetitions before the pavement develops 20% fatigue cracking et = Initial horizontal tensile strain at the bottom of bituminous layer Eac = Elastic Modulus of bituminous layer, MPa NR = 4.1656 * 10-8 (1/ez)4.5337 NR = Cumulative std. Axle load repetitions before the pavement develops 20 mm average rut depth ez = Initial vertical strain on top of subgrade
- 143. BITS Pilani, Hyderabad Campus For design of bituminous overlay, a trial thickness of overlay of an appropriate material has to be selected and the critical strains have to be evaluated. The modulus value of the bituminous overlay material may be selected as per the guidelines given in IRC:37-2012 (x) Design overlay thickness can be selected by trial in such a way that the computed critical strains are less than the permissible limits given by the performance criteria for the design traffic level considered. OVERLAYDESIGN METHODOLOGY
- 144. BITS Pilani, Hyderabad Campus Design traffic = 100 msa Thicknesses :- Bit. Layer = 95, Granular = 540 Deflections measured in January Pavement Surface Temperature = 35 0C Surface Deflections measured using FWD and normalised for 40 kN are :- 0.73517, 0.43835, 0.28919, 0.21580, 0.16638, 0.13406 mm Back calculated Moduli (MPa) are :- 1350.4, 172.7, 52.5 Design Example
- 145. BITS Pilani, Hyderabad Campus Subgrade Modulus corrected for season = 43.6 MPa E(sub_mon) = 28.39+0.2888 E(sub_win) Tensile Strain = 0.0004294; Vertical Strain = 0.0007214; Remaining life :- 3.5 msa (Rutting); 5.9 msa (fatigue) Providing a 160 mm BC overlay (E of 1695 MPa) the life extends to 123.5 msa (Rutting) and 124.9 msa (fatigue) Design Example
- 146. BITS Pilani, Hyderabad Campus IRC:37-2012, "Tentative Guidelines for the Design of Flexible Pavements", Indian Roads Congress, New Delhi. B.B. Pandey, "Structural Evaluation of Pavements using Falling Weight Deflectometer", IIT Kharagpur. Dr. K. Sudhakar Reddy, “Pavement Evaluation and Rehabilitation IRC:81- 1997 & IRC:115-2014” IIT Kharagpur. IRC:81-1997, "Guidelines for Strengthening of Flexible Road Pavements Using Benkelman Beam Technique", Indian Roads Congress, New Delhi. IRC:115-2014, "Guidelines For Structural Evaluation And Strengthening Of Flexible Road Pavements Using Falling Weight Deflectometer (FWD) Technique”, Indian Roads Congress, New Delhi References