1 Principles of Pavement Design
Principles of Pavement Design
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Principles of Pavement Design

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Principles of Pavement Design . G. Kavitha, FacultyRASTA, Center for Road TechnologyVTU Extension CenterBangalore. Requirements of PavementsPavement types and their choiceDesign factors for flexible pavementsDesign of flexible pavements by CBR method. Outline. Base. Black Topping. Road Composition.
Principles of Pavement Design

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1. This is the first slide of the presentationThis is the first slide of the presentation

2. In the second slide, the tiltle of the presentation and the name of the speaker is provided, many such slides can be included with the content of the subjectsIn the second slide, the tiltle of the presentation and the name of the speaker is provided, many such slides can be included with the content of the subjects

3. Requirements of Pavements Pavement types and their choice Design factors for flexible pavements Design of flexible pavements by CBR method Outline

4. Whenever the pavement has to be raised above the existing ground level, embankment has to be constructed. This is essential to keep the subgrade above the high water table, tp prevent damage of the pavement due to surface water and capillary water and to maintain the design standards of highway with respect to vertical alignmentWhenever the pavement has to be raised above the existing ground level, embankment has to be constructed. This is essential to keep the subgrade above the high water table, tp prevent damage of the pavement due to surface water and capillary water and to maintain the design standards of highway with respect to vertical alignment

5. Structural Requirements Traffic loads Load repetition Climatic variables (rainfall & temperature) Environmental factors (water table, embankment) The total thickness of the pavement and the thickness of the individual pavement layers should be sufficient to withstand the heavy traffic loads and the repetition of wheel loads of different magnitudes so that the stresses induced on the pavement are within the permissible limits, under the existing climatic and environmental conditions. The climatic conditions could be the variation in the rainfall and temperature and the environmental factors like height of embankment, depth of water table can also affect the structural capacity of the pavements. We will study these factors in detail in the subsequent slides.The total thickness of the pavement and the thickness of the individual pavement layers should be sufficient to withstand the heavy traffic loads and the repetition of wheel loads of different magnitudes so that the stresses induced on the pavement are within the permissible limits, under the existing climatic and environmental conditions. The climatic conditions could be the variation in the rainfall and temperature and the environmental factors like height of embankment, depth of water table can also affect the structural capacity of the pavements. We will study these factors in detail in the subsequent slides.

6. Functional Requirements Riding comfort Economic operation Safe operation The pavement should provide good riding quality for the vehicles moving at design speed through out its service life. The unevenness / undulations cause vertical oscillations of the vehicles resulting in poor riding comfort. The undulations also increase the vehicle operation cost. Also if the pavement surface is very slippery then it results in skidding of the vehicles and results in unsafe operations. therefore the functional requirement of the pavements is to provide safe, comfortable and fast movement of vehicles and goods at reasonable low vehicle vehicle operation cost.The pavement should provide good riding quality for the vehicles moving at design speed through out its service life. The unevenness / undulations cause vertical oscillations of the vehicles resulting in poor riding comfort. The undulations also increase the vehicle operation cost. Also if the pavement surface is very slippery then it results in skidding of the vehicles and results in unsafe operations. therefore the functional requirement of the pavements is to provide safe, comfortable and fast movement of vehicles and goods at reasonable low vehicle vehicle operation cost.

7. Pavement Types Flexible pavements are those pavements which have low flexural strength. They are made up of a number of granular and bituminous layers which transmit the vertical or compressive stresses to the lower layers by grain to grain and thus distribute the stresses to a larger area in the shape of a truncated cone. The rigid pavements have good flexural strength and the stresses are transmitted through a wider area below through the slab action. Flexible pavements are those pavements which have low flexural strength. They are made up of a number of granular and bituminous layers which transmit the vertical or compressive stresses to the lower layers by grain to grain and thus distribute the stresses to a larger area in the shape of a truncated cone. The rigid pavements have good flexural strength and the stresses are transmitted through a wider area below through the slab action.

8. Stresses in Flexible pavements This is how the stresses are distributed in the flexible pavement structure. The vertical compressive stress is maximum on the pavement surface directly under the wheel load and is equal to the contact pressure under the wheel. Due to the ability to distribute the stresses to a larger area the stresses get decreased at the lower layers is very low / negilgible.This is how the stresses are distributed in the flexible pavement structure. The vertical compressive stress is maximum on the pavement surface directly under the wheel load and is equal to the contact pressure under the wheel. Due to the ability to distribute the stresses to a larger area the stresses get decreased at the lower layers is very low / negilgible.

11. As seen in the sketch, the influence of tyre pressure is predominant in the upper layers. At a greater depth the effect of tyre pressure dimishes and the total load exhibits a considerable influence on the vertical stress magnitudes. Tyre pressure of high magnitude therefore demand high quality of materials in the upper layers in pavements. The total depth of pavement is however not influenced by the tyre pressure.As seen in the sketch, the influence of tyre pressure is predominant in the upper layers. At a greater depth the effect of tyre pressure dimishes and the total load exhibits a considerable influence on the vertical stress magnitudes. Tyre pressure of high magnitude therefore demand high quality of materials in the upper layers in pavements. The total depth of pavement is however not influenced by the tyre pressure.

12. In the cc pavements the load carrying capacity is mainly due to the rigidity and high modulus of elasticity of the slab itself.. Slab action. We provide a drainage layer above that DLC subbase course, which mainly prevents pumping under the pavement, to control differential frost action and to provide a strong structural support during for construction equipment during concreting of slabsIn the cc pavements the load carrying capacity is mainly due to the rigidity and high modulus of elasticity of the slab itself.. Slab action. We provide a drainage layer above that DLC subbase course, which mainly prevents pumping under the pavement, to control differential frost action and to provide a strong structural support during for construction equipment during concreting of slabs

13. Semi Rigid Pavements Intermediate class of materials used in base / sub base course The intermediate materials are ? bonded materials like lime fly ash aggregate mix (puzzolanic concrete), lean cement concrete or soil cement They have slightly high flexural strength than the flexible pavements They do not possess as much flexural strength as cement concrete pavements These materials have low resistance to impact and abrasion

14. Choice Of Pavement Type Initial cost Maintenance cost Total transportation cost Availability of funds

15. Design Factors For Flexible Pavements Design Wheel Load Sub-grade Support Materials in Pavement Component layers Climatic and Environmental Factors Drainage Characteristics Various factors to be considered for the design of flexible pavements are as follows???.. Various factors to be considered for the design of flexible pavements are as follows???..

16. Load Gross load, ?P? Tyre and Contact pressure, ?p? or the area of contact, A Multiple wheel load and ESWL Repeated application of wheel loads and EWL factors - P1 N1 = P2 N2 Cumulative standard axles, CSA in msa Other factors - pavement width lane distribution factor, speed etc. The various wheel load factors to be considered are maximum wheel load or the gross load which influences the thickness requirements of pavements. As per IRC the legal single axle load is 8170 kg which is now revised to 10.2 tonnes. Contact pressure ? when the tyre pressure is higher, higher is the contact area and hence lesser is the contact pressure. When the contact pressure is lesser, higher tyre pressure demand high quality of materials in the upper layers as the surface pressure is high. To maintain the maximum wheel load within the specified limit and to carry greater loads it is necessary to dual and multiple wheel load assembly to the rear axles of the vehicles. In doing so the effect of the dual wheel assembly is not same as two times the load on any one wheel, but the effect is in betn single load and the two times the load carried by any one wheel. The dual or multiple wheel loads is converted to ESWL which is used in the pavement design. This ESWL is defined as that single wheel load which produces the same value of maximum deflection or stress at the desired depth z of the pavement. Repeated application of wheel loads ? the deformation of the pavement due to the single application of a wheel load is small but due to repeated application of the wheel loads, there is increased magnitude of plastic and elastic deformation. This accumulated permanent deformation of the pavement results in pavement failure. The repeated application of wheel loads of different magnitudes are converted to a single load equivalent to the repeated application of any particular wheel load, using equivalent load factors. CSA ? as per IRC 37-2001, flexible pavements are designed based on the cumulative number of standard axle loads and not the total number of the commercial vehicles. The mixed commercial vehicles with different axle loads are converted to CSA. The various wheel load factors to be considered are maximum wheel load or the gross load which influences the thickness requirements of pavements. As per IRC the legal single axle load is 8170 kg which is now revised to 10.2 tonnes. Contact pressure ? when the tyre pressure is higher, higher is the contact area and hence lesser is the contact pressure. When the contact pressure is lesser, higher tyre pressure demand high quality of materials in the upper layers as the surface pressure is high. To maintain the maximum wheel load within the specified limit and to carry greater loads it is necessary to dual and multiple wheel load assembly to the rear axles of the vehicles. In doing so the effect of the dual wheel assembly is not same as two times the load on any one wheel, but the effect is in betn single load and the two times the load carried by any one wheel. The dual or multiple wheel loads is converted to ESWL which is used in the pavement design. This ESWL is defined as that single wheel load which produces the same value of maximum deflection or stress at the desired depth z of the pavement. Repeated application of wheel loads ? the deformation of the pavement due to the single application of a wheel load is small but due to repeated application of the wheel loads, there is increased magnitude of plastic and elastic deformation. This accumulated permanent deformation of the pavement results in pavement failure. The repeated application of wheel loads of different magnitudes are converted to a single load equivalent to the repeated application of any particular wheel load, using equivalent load factors. CSA ? as per IRC 37-2001, flexible pavements are designed based on the cumulative number of standard axle loads and not the total number of the commercial vehicles. The mixed commercial vehicles with different axle loads are converted to CSA.

17. Subgrade Soil type and index properties Strength properties (CBR, K - value or E-value) Drainage characteristics Before designing the pavement, it is essential to know the type of soil (wet sieve analysis) available in the particular vicinity and also study some of the properties of the soil like index properties which includes ? LL, PL and P.I. since subgrade soil serves as the foundation of the pavement, we should ensure that the locally available soil fulfills the specific requirements. The strength of the soil like CBR helps in deciding the thickness requirement of the pavements. A subgrade with low CBR requires thicker pavement and vice versa. Since CBR is only a strength number and doesnot relate to any fundamental properties of the soil it is essential to also determine K value ? modulus of subgrade reaction by plate load test and E ? value by direct shear or triaxial compression test. Performance of the pavement also depends on the drainage characteristics of the subgrade. Soils like silt and silty sand have poor permeability and therefore help in frost action in regions where temperature can fall below zero degreesBefore designing the pavement, it is essential to know the type of soil (wet sieve analysis) available in the particular vicinity and also study some of the properties of the soil like index properties which includes ? LL, PL and P.I. since subgrade soil serves as the foundation of the pavement, we should ensure that the locally available soil fulfills the specific requirements. The strength of the soil like CBR helps in deciding the thickness requirement of the pavements. A subgrade with low CBR requires thicker pavement and vice versa. Since CBR is only a strength number and doesnot relate to any fundamental properties of the soil it is essential to also determine K value ? modulus of subgrade reaction by plate load test and E ? value by direct shear or triaxial compression test. Performance of the pavement also depends on the drainage characteristics of the subgrade. Soils like silt and silty sand have poor permeability and therefore help in frost action in regions where temperature can fall below zero degrees

18. Pavement Materials Materials characteristics in different layers (Stress distribution, drainage, strength factor etc) Durability Fatigue effects It is essential to evaluate the properties of the various materials used in different layers of the pavement in order to ensure good strength, durability under adverse conditions of weather and fatigue behaviour of these materials for better performance of the pavements. The stress distribution characterisitics of the pavement component layers depend on the characteristics of the material Some of the properties determined are: CBR, Elastic moduli, subgrade modulusIt is essential to evaluate the properties of the various materials used in different layers of the pavement in order to ensure good strength, durability under adverse conditions of weather and fatigue behaviour of these materials for better performance of the pavements. The stress distribution characterisitics of the pavement component layers depend on the characteristics of the material Some of the properties determined are: CBR, Elastic moduli, subgrade modulus

19. Climatic And Environmental Factors Rain fall Depth of water table and relative height of formation Sub-grade moisture content for design Temperature variations - daily and seasonal Frost action Pavement performance is affected by the variation in moisture due to variation in rainfall, soil type, ground water level, drainage conditions etc. the surface water during rains may enter the subgrade through the pavement edges or through the porous pavement surface itself. The subgrade moisture may also vary due to fluctuations in the ground water table. It also depends on capillary action. This variations in moisture can be controlled by providing suitable surface and sub surface drainage system. Frost action ? the alternate cycles of frost heaving and thaw is called frost action. The held water in the subgrade forms ice crystals, when the temperature reduces below zero degrees. These grow in size with the continuous supply of water due to capillary action. This results in raising of the pavement structure known as frost heave. Subsequent increase in temperature would result in melting or thawing of the frozen ice crystals and soften the road bed, hence voids are created by the melted ice crystals. Temperature stresses of high magnitude are induced in cement concrete pavements due to daily and seasonal variations in temperature. In bituminous pavements the bituminous mix softens in hot weather and brittle in cold weatherPavement performance is affected by the variation in moisture due to variation in rainfall, soil type, ground water level, drainage conditions etc. the surface water during rains may enter the subgrade through the pavement edges or through the porous pavement surface itself. The subgrade moisture may also vary due to fluctuations in the ground water table. It also depends on capillary action. This variations in moisture can be controlled by providing suitable surface and sub surface drainage system. Frost action ? the alternate cycles of frost heaving and thaw is called frost action. The held water in the subgrade forms ice crystals, when the temperature reduces below zero degrees. These grow in size with the continuous supply of water due to capillary action. This results in raising of the pavement structure known as frost heave. Subsequent increase in temperature would result in melting or thawing of the frozen ice crystals and soften the road bed, hence voids are created by the melted ice crystals. Temperature stresses of high magnitude are induced in cement concrete pavements due to daily and seasonal variations in temperature. In bituminous pavements the bituminous mix softens in hot weather and brittle in cold weather

20. Good drainage facilities both surface and sub surface should be provided in order to prevent the damage cause to the pavement due to accumulation of water. These drainage structures should also be well maintained inorder to continue working effectively.Good drainage facilities both surface and sub surface should be provided in order to prevent the damage cause to the pavement due to accumulation of water. These drainage structures should also be well maintained inorder to continue working effectively.

21. Flexible Pavement Design Basic Principles Vertical stress or strain on sub-grade Tensile stress or strain on surface course Two critical stresses considered in the design of flexible pavements are vertical compressive stress on the subgrade which results in permanent deformation or rutting and horizontal tensile strain on the surface course resulting in cracks.Two critical stresses considered in the design of flexible pavements are vertical compressive stress on the subgrade which results in permanent deformation or rutting and horizontal tensile strain on the surface course resulting in cracks.

22. Evaluation Of Pavement Component Layers Sub-grade To Receive Layers of Pavement Materials Placed over it Plate Bearing Test CBR Test Triaxial Compression Test

23. Evaluation Of Pavement Component Layers Sub-base And Base Course - To Provide Stress Transmitting Medium To distribute Wheel Loads To Prevent Shear and Consolidation Deformation In case of rigid pavements to Prevent pumping Protect the subgrade against frost action - Plate Bearing Test CBR Test

24. Wearing Course High Resistance to Deformation High Resistance to Fatigue; ability to withstand high strains - flexible Sufficient Stiffness to Reduce Stresses in the Underlying Layers High Resistance to Environmental Degradation; durable Low Permeability - Water Tight Layer against Ingress of Surface Water Good Workability ? Allow Adequate Compaction Sufficient Surface Texture ? Good Skid Resistance in Wet Weather - bituminous materials used in wearing course tested by Marshall test

25. Flexible Pavement Design Using CBR Value Of Sub-grade Soil California State Highways Department Method Required data Design Traffic in terms of cumulative number of standard axles(CSA) CBR value of subgarde

26. Traffic Data Initial data in terms of number of commercial vehicles per day (CVPD) Traffic growth rate during design life in % Design life in number of years Distribution of commercial vehicles over the carriage way

27. Traffic ? In Terms Of CSA (8160 Kg) During Design Life Initial Traffic In terms of Cumulative Vehicles/day Based on 7 days 24 hours Classified Traffic Traffic Growth Rate Establishing Models Based on Anticipated Future Development or based on past trends Growth Rate of LCVs, Bus, 2 Axle, 3 Axle, Multi axle, HCVs are different 7.5 % may be Assumed

28. Design Life National Highways ? 15 Years Expressways and Urban Roads ? 20 Years Other Category Roads ? 10 ? 15 Years

29. Vehicle Damage Factor (VDF) Multiplier to Convert No. of Commercial Vehicles of Different Axle Loads and Axle Configurations to the Number of Standard Axle Load Repetitions indicate VDF Values Normally = (Axle Load/8.2)n n = 4 - 5

30. VEHICLE DAMAGE FACTOR (VDF)

31. VEHICLE DAMAGE FACTOR (VDF)

32. Vehicle Damage Factor (VDF)

33. Vehicle Damage Factors LCV - 0.259 2-Axle Trucks - 4.95 3- Axle Trucks - 7.587 BUS - 1.027 MULTI-AXLE TRUCKS - 9.535

34. INDICATIVE VDF VALUES

35. Single Lane Roads Total No. of Commercial Vehicles in both Directions Two-lane Single Carriageway Roads 75% of total No. of Commercial Vehicles in both Directions Four-lane Single Carriageway Roads 40% of the total No. of Commercial Vehicles in both Directions Dual Carriageway Roads 75% of the No. of Commercial Vehicles in each Direction An assessment of the distribution of commercial traffic by direction and by lane is necessary as it affects the total equivalent std axle load used in the designAn assessment of the distribution of commercial traffic by direction and by lane is necessary as it affects the total equivalent std axle load used in the design

36. Computation of Traffic for Use of Pavement Thickness Design Chart 365 xA[(1+r)n ? 1] N = --------------------------- x D x F r N = Cumulative No. of standard axles to be catered for the design in terms of msa D = Lane distribution factor A = Initial traffic, in the year of completion of construction, in terms of number of commercial vehicles per day F = Vehicle Damage Factor n = Design life in years r = Annual growth rate of commercial vehicles

37. Computation Of CSA For Different Vehicle Classes

44. Subgrade Subgrade to be Well Compacted to Utilize its Full Strength Top 500 mm to be Compacted to 97% of MDD (Modified Proctor) Material Should Have a Dry Density of 1.75 gm/cc CBR to be at Critical Moisture Content and Field Density Strength ? Lab. CBR on Remoulded Specimens and NOT Field CBR

45. Subgrade Soak the Specimen in Water for FOUR days and CBR to be Determined Use of Expansive Clays NOT to be Used as Sub-grade Non-expansive Soil to be Preferred If ARF < 500 mm, Soaking is NOT required

46. Permissible Variation in CBR Value

47. Sub-base Material ? Natural Sand, Moorum, Gravel, Laterite, Kankar, Brick Metal, Crushed Stone, Crushed Slag, Crushed Concrete GSB- Close Graded / Coarse Graded Parameters ? Gradation, LL, PI, CBR Stability and Drainage Requirements

48. Sub-base Min. CBR 20 % - Traffic up-to 2 msa Min. CBR 30 %- Traffic > 2 msa If GSB is Costly, Adopt WBM, WMM Should Extend for the FULL Width of the Formation Min. Thickness ? 150 mm - <10 msa Min. Thickness ? 200 mm - >10 msa

49. Sub-base Min. CBR ? 2 % If CBR < 2% - Pavement Thickness for 2 % CBR + Capping layer of 150 mm with Min. CBR 10% (in addition to the Sub-Base) In case of Stage Construction ? Thickness of GSB for Full Design Life

50. Base Course Unbound Granular Bases ? WBM / WMM or any other Granular Construction Min. Thickness ? 225 mm ? < 2 msa Min. Thickness ? 250 mm - > 2 msa WBM ? Min. 300 mm ( 4 layers ? 75mm each)

51. Bituminous Surfacing Wearing Course ? Open Graded PMC, MSS, SDBC, BC Binder Course ? BM, DBM BM- Low Binder, More Voids, Reduced Stiffness,

52. Bituminous Surfacing Provide 75 mm BM Before Laying DBM Reduce Thickness of DBM Layer, when BM is Provided ( 10 mm BM = 7 mm DBM) Choice of Wearing Course ? Design Traffic, Type of Base / Binder Course, Rainfall etc

53. Choice Of Wearing Courses

54. Appraisal Of CBR Test And Design Strength Number and Cannot be Related Fundamental Properties Material Should Pass Through 20 mm Sieve Surcharge Weights to Simulate Field Condition Soaking for Four Days- Unrealistic CBR Depends on Density and Moisture Content of Sub-grade Soil Design Based on Weakest Sub-grade Soil Encountered

55. Example Of Pavement Design For A New Bypass

56. DATA: Two-lane single carriageway = 400 CV/day (sum of both directions) Initial traffic in a year of completion of construction Traffic growth rate per annum = 7.5 percent Design life = 15 years Vehicle damage factor = 2.5 (standard axles per commercial vehicle) Design CBR value of sub-grade soil = 4 %

58. Pavement Composition interpolated From Plate 1, CBR 4% (IRC37-2001) Bituminous surfacing = 25 mm SDBC + 70 mm DBM Road base, WBM = 250 mm Sub-base = 315 mm

59. Example Of Pavement Design For Widening An Existing 2-lane NH To 4-lane Divided Road

61. Distribution factor = 0.75 VDF = 4.5 CSA for 10 Years = 100 msa CSA for 15 years = 185 msa Pavement thickness for CBR 5% and 100 msa for 10 Years = 745 mm For 185 msa for 15 years = 760 mm Provide 300 mm GSB + 250 mm WMM + 150 mm DBM + 50 mm BC (10 years) Provide 300 mm GSB + 250 mm WMM + 170 mm DBM + 50 mm BC (15 years)

63. This is the last slide This is the last slide


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