guidelines for design of flexible pavementpresentation.pptx

its a guideline for desgin of flexible pavement .

1. Guidelines for the Design of Flexible Pavements-2014 (Second Edition 2021)

2. Importance of Highway Pavements Foundation of Highway Construction Impact on Road Sector Performance Interrelation with Costs and Economics Global Practices and Methods

3. Objectives of the Guidelines Guidance for Engineers Economic Considerations Consideration of Construction Trends Proposal of Suitable Pavement Structures Incorporation of Recent Research Outcomes

4. Evolution and Need for Revision Formulation in 2014 : DoR established the 'Guidelines for the Design of Flexible Pavement' in 2014. Initial principles were adopted from ORN-31, IRC-37-2001, and AASHTO, tailored to Nepal's context. Withdrawal of 1st Edition : The first edition of the guidelines was withdrawn for pavement design purposes due to evolving factors. Need for Revision : Changes in vehicular technology, loading patterns, and freight traffic intensity necessitated a revision of design methods. Fundamental issues required updating to align with current practices and research outcomes.

5. Evolution and Need for Revision(cont...) IRC Guidelines Revision : The IRC (Indian Roads Congress) guidelines were revised in 2018, prompting a review of Nepal's pavement design standards. Initiation of Revision : DoR initiated the revision of the guidelines to incorporate recent research findings and advancements in construction and vehicular technology. Considerations for Revision : The revision process took into account trends in construction practices and evolving vehicular technologies to ensure updated and effective guidelines.

6. Scope and Applicability Designed for National Highways and urban highways with traffic volumes exceeding 2 million standard axles ( msa ). Provides guidance on selecting pavement types based on traffic characteristics.

7. Pavement Type Selection Primary Factors Secondary Factors

8. Primary Factors: Traffic volume and loading characteristics Soil load-bearing capacity Climate conditions impacting pavement performance Construction constraints and staging requirements Recycling opportunities and cost considerations Secondary Factors: Past performance of similar pavements Continuity with adjacent existing pavements Material and energy conservation Local material availability and contractor capabilities Traffic safety and delineation needs Experimental considerations and promotion of competition Local industry preferences

9. Pavement as a Multi-layered System Pavement analyzed using linear elastic layered theory. Sub-grade, base, binder, and surface layers modeled for stress and strain. Mechanistic parameters include rutting, bottom-up cracking, and fatigue resistance. Recommendations for layer compositions and properties.

10. Performance Criteria Criteria for sub-grade rutting, fatigue cracking, and CTB performance. Equations for calculating cumulative axle load repetitions before failure conditions occur. Reliability levels (80% and 90%) based on traffic volume.

11. Design Reliability 90% reliability recommended for Expressways, National Highways, State Highways, and Urban Roads. 80% reliability for roads with lower traffic volumes.

12. Flexible Pavement Analysis Analysis based on linear elastic layered system. Critical parameters include strains and stresses in different layers. Use of IITPAVE or DoR software for analysis under standard conditions.

13. 4.TRAFFIC Introduction

14. Impact of Traffic on Pavement Road damage is mainly caused by the weight of vehicles and how often they travel. Passenger cars don't damage the pavement much. We focus on heavy vehicles like trucks for pavement design because they cause most of the damage.

15. Different types of failure encountered in flexible pavements are as follow. 1. Alligator cracking or Map cracking (Fatigue) 2. Consolidation of pavement layers (Rutting) 3. Shear failure cracking 4. Longitudinal cracking 5. Frost heaving 6. Lack of binding to the lower course(Potholes & Sleepage ) 7. Reflection cracking 8. Formation of waves and corrugation 9. Bleeding 10. Pumping Failures caused in flexible pavement

16. Fatigue cracking Rutting

17. Shear failure cracking Longitudinal cracking

18. Frost heaving Lack of binding to the lower course

19. Reflection cracking Formation of waves and corrugation

20. Bleeding Pumping

21. Design Traffic Estimation Design traffic is estimated in terms of equivalent standard axles. Inputs required for this estimation include: Initial traffic volume Traffic growth rate Design life Axle load spectrum Lateral distribution factors. If we don't have enough data, we assume a minimum growth rate, usually around 5% per year for commercial vehicles.

22. National Highways = 20 years. Expressways pavement =30 years Low volume roads =10 years. Design Periods

23. Axle Configurations An axle is a central shaft for a rotating wheel or gear

24. Standard Axle Single axle with dual wheels carrying a load of 80 kN (8 tonnes ) is defined as standard axle.

25. Vehicle Damage Factor (VDF) What is VDF? Why is VDF Important? How is VDF Calculated? Axle Load Survey

26. Lateral Distribution of commercial traffic over the carriageway: Single Lane Roads Intermediate Lane Roads (5.5m wide)=75% of the two-way commercial traffic. Two-Lane Two-Way Roads= 50% of the two-way commercial traffic Four-Lane Single Carriageway Roads= 40% of the two-way commercial traffic Dual Carriageway Roads= -For dual two-lane roads=75% of the commercial vehicles in each direction. - For dual three-lane roads, it's 60%. - And for dual four-lane roads, it's 45%.

27. Traffic Forecasting Base Year Traffic Flow : Traffic Forecasting: Normal Traffic: They forecast it by looking at past trends and assuming similar growth rates. Diverted Traffic: They assume it will grow at the same rate as traffic on the road it came from. Generated Traffic: It's tough to predict and can vary greatly depending on the situation.

28. Computation of design traffic

29. PAVEMENT SUB-GRADE Layers of flexible pavements

30. Flexible pavement consists of layers: sub-base, base, and bituminous layers. Sub-base and base layers can be granular, cement-treated, or a mix of both. Crack relief layer required for cement-treated base. Sub-grade is top 500 mm below pavement; level difference to water table should be ≥1.0 m. Compaction crucial for sub-grade strength; heavy compaction recommended for major roads. Standard specifications outline capping, mechanical, and lime stabilization for sub-grade. CBR value of soil determines design: 90th percentile for high-volume roads, 80th for low traffic.

31. Resilient Modulus of the Sub-grade: Resilient modulus measures how much a material can bounce back after being compressed. For sub-grade soil, we typically estimate the resilient modulus (MRS) from its California Bearing Ratio (CBR) value. Here are the equations: If CBR ≤ 5%: MRS =10.0× CBR If CBR > 5%: 17.6×( CBR /5%)0.64 Poisson's ratio for sub-grade soil is usually taken as 0.35.

32. Effective Modulus/CBR for Design: Here's how to do it: We figure out the maximum surface deflection (σ) caused by a single wheel load on the sub-grade and embankment layers. We can use specific equations and software to calculate this. b) Then, we calculate the effective resilient modulus (MRS) using this equation: MRS = σ / μa 2(1− μ 2)​ In this equation: μ is Poisson's ratio (usually taken as 0.35). σ is the maximum surface deflection. a is the radius of the circular contact area, which we can calculate using the load applied (40,000 N) and the contact pressure 'p' (0.56 MPa ); this comes out to be 150.8 mm.

33. If CBR is less than 5%, Capping Layer Material (CBR>15%) shall be used as subgrade, and effective CBR shall be calculated from above graph. Example: If Ground CBR is 2%, and we propose Capping Layer of 20% CBR, the effective CBR for pavement design is 8.5%. (Source IRC 37: 2012) Embankment/cut/ Levelled ground(500mm)

34. 6. Sub base Layer of aggregate material laid on the subgrade on which the base course layer is loacted Types: Granular Sub-base layer Cement Treated Sub-base(CSTB)layer

35. 6.1 Granular Sub-base layer Supporting the compacted granular base (WMM/ WBM) layer Protect the sub-grade from overstressing and serving as drainage and filter layers Follow Standard Specification for Road and Bridge Works 2073

36. REQUIRMENTS: Gradings III and IV shall preferably be used in lower sub-base layer Gradings V and VI shall be used as sub-base cum drainage layer The minimum thickness of drainage as well as filter layer (two layers) shall not be less than 200 m The minimum thickness of a single filter-cum-drainage layer shall be 150 mm for functional requirement The minimum thickness of any compacted granular layer should preferably be at least 2.5 times the nominal maximum size of aggregate subject to a minimum of 100mm The two-layer system (sub-grade and GBS) should be analyzed by placing a standard load over it (dual wheel set of 20,000 N each creating the contact pressure of 0.56 MPa) and computing (Using IITPAVE software or Software developed by DoR ) the maximum sub-grade vertical compressive strain

37. 6.2 Resilient Modulus of Granular Sub-base (GSB) layer Depend on the resilient modulus value of the foundation or supporting layer on which it rests and the thickness of the Granular Sub-base layer. M RGRAN = 0.2 h 0.45 MR SUPPORT * Where, h = Thickness of the granular layer M RGRAN = Resilient Modulus of the granular layer (MPa) M RSUPPORT = Effective Resilient Modulus of the supporting layer (MPa)

38. 6.3 Cement Treated Sub-base (CTSB) Layer Construction is mentioned in SSRBW, 2073. Material: Soil including sand and gravel, laterite, kankar , brick aggregate, crushed rock or slag or their combination Uniformity coefficient not less than 5 Well graded and have a grading within the range given in Table 12.3 Pass through 425 micron sieve, liquid limit not greater than 45 percent and plasticity index not greater than 20 percent

39. 6.4 Mechanical properties of CTSB elastic modulus (E) of the CTSB material may be estimated from the Unconfined Compressive Strength (UCS) of the material The cement Treated Sub-base (CTSB) should have a 7-day UCS of 1.5 to 3.0 MPa. Third point loading test flexural modulus ECGSB of 28-day cured CTSB material E CTSB =1000*UCS Equation 17 Where, UCS = 28-day unconfined compressive strength (MPa) of the cementitious granular material. It should be ensured E CTSB = Elastic modulus (MPa) of 28-day cured CTSB material

40. BASE COURSE UNBOUNDED LAYER CEMENTITIOUS BASE LAYER FLEXURAL STRENGTH(MODULUS OF RUPTURE) of CTB material FLEXURAL STRENGTH(MODULUS OF RUPTURE) OF CTB MATERIAL DURABILITY CRITERIA

41. 7.1 Unbound Base layer Types such as Water Bound Macadam base (Clause 1203), Crusher Run Macadam base (clause 1204), Telford Base (Clause 1206), Dry Bound base (1207) and Wet Mix macadam (1208) base. Prepared under Standard Specifications for Road and Bridge Works. Grading and physical requirements for respective types as mentioned in the Standard Specifications. Minimum thickness of granular base is 150 mm. Resilient modulus of the granular base can be estimated using Equation 16 taking MRGRAN as the modulus of the combined (GSB and Granular base) granular layer in MPa, ‘h’ as the combined thickness (mm) of the granular sub-base and base and M RGRAN = 0.2 h 0.45 M RSUPPORT

42. 7.2 Cementitious base layer Grading within the range given in Table 12.3. Material pass through 425 micron sieve , liquid limit not greater than 45 per cent and plasticity index not greater than 20 percent determined in accordance with IS:2720 (Part 5). The CTB material shall have a minimum unconfined compressive strength (UCS) of 4.5 to 7 MPa in 7/28 days Considered in the case of subbase, average laboratory strength values should be 1.5 times the required minimum (design) field strength. The thickness of cement treated bases shall not be less than 100 mm Unconfined compression strength values ranging between 4.5 to 7 MPa

43. Flexural strength (modulus of rupture) of CTB material Values of modulus of rupture (MPa) for cementitious bases may be taken as 20 per cent of the 28-day UCS value (MPa), subject to the following limiting values: Cementitious stabilized aggregates: 1.40 MPa • Lime- flyash -soil: 1.05 MPa Soil-cement: 0.70 MPA Durability Criteria wetting and drying test freezing and thawing test(Cold and snow bound region)

44. 7.3 Crack Layers Cracked relief layers Comprise of either dense graded crushed aggregates with a thickness of 100 mm, meeting Wet Mix Macadam (WMM) specifications, or a Stress Absorbing Membrane Interlayer (SAMI) made of elastomeric modified binder applied at a rate of 10-12 kg per 10 m², covered with 0.1 m³ of 11.2 mm aggregates Not included in the pavement structure when evaluating its performance or characteristics.

45. 8.Bituminous layer 8.1 General Bituminous surfacing includes wearing course or binder course based on traffic. For high traffic (>50 msa), recommend: Stone Matrix Asphalt (SMA) with modified binders Gap Graded mix with rubberized bitumen (GGRB) Bituminous Concrete (BC) with modified binders Medium traffic (20-50 msa) uses BC with VG40 bitumen. Low traffic (<20 msa) prefers Bituminous Concrete (BC), Pre-Mix Carpet (PMC), or Surface Dressing (SD) with unmodified binders.

46. Table : Summary of Bituminous layer options recommended in these guidelines [1]

47. 8.1.1Bitumen Types and Pavement Temperatures Use :- VG40 for higher traffic and modified bitumen for durability. VG30 is suitable for lower traffic. VG10 for snow-bound locations. Mastic Asphalt for roads in high rainfall areas and junction locations.

48. 8.2 Resilient modulus of bituminous mixes Resilient modulus varies based on binder grade, air voids, aggregate properties, etc. Table : Indicative values of resilient modulus (MPa) of bituminous mixes [1]

49. Measurement Standards Resilient modulus measured at 35°C per ASTM 4123 with Poisson's ratio of 0.35 and in snowboard at 20°C. Measurement of the resilient modulus of DBM, 150 mm diameter specimens should be used.

50. Design Considerations Bituminous layers treated as one in pavement analysis with assigned elastic properties. DBM mix modulus value used for analysis and design, especially for bottom DBM layer. Maximum modulus values from Table guide pavement design at 35°C average annual temperature .

51. Empirical Relationships Resilient Modulus of 150 mm diameter DBM specimens at 35°C Resilient Modulus of 102 mm diameter specimens with elastomeric polymer modified binder mixes at 35°C Where, ITS = Indirect tensile Strength in kPa Mr = resilient Modulus in MPa

52. Bitumen-Rich DBM Bottom Layer Recommended for longer life of bituminous pavements. To avoid moisture induced distresses. Provides better bottom-up fatigue resistance.

53. Design Characteristics Compaction to smaller in-place air voids results in stiffer mixes and reduces rutting under traffic stresses. Higher binder volume with reduced air voids for increased binder content.

54. Thickness requirement Follow relevant Standard Specifications for minimum thickness of bituminous layers. For traffic exceeding 20 msa, ensure combined surface course and base/binder course thickness of at least 100 mm.

55. 9. LONG-LIFE PAVEMENTS Long-life pavements are designed for 50+ years, termed as perpetual pavements. Recommended for design traffic of 300 msa (million standard axles) or more.

56. Endurance Limits (Asphalt Institute, MS-4) Tensile strain < 70 microstrain prevents cracking. Vertical sub-grade strain < 200 microstrain minimizes rutting.

57. Design Approach Select pavement layers to limit strains within endurance values. Maintain horizontal tensile and vertical compressive strains within limits. Annex-C provides a detailed design example for long-life pavement.

58. 10. PAVEMENT DESIGN PROCEDURE : 10.1 Design steps Selecting a trial composition: strong sub-grade, a well-drained sub-base strong enough to withstand the construction traffic loads a strong bituminous base that is resistant to crack, rutting and moisture damage a bituminous surfacing that is resistant to rutting,top -down cracking and damages caused by exposure to environment.

59. 2. Bituminous Mix design and the mix resilient modulus: The ingredients for the mix have to be decided and the physical requirements/ properties of the sourced materials shall be checked for their conformity with the provisions of applicable Specifications and Guidelines. The right proportioning of the mix ingredients or the design mix should be achieved by trials and testing. Where the resilient modulus is required to be tested in accordance with the procedures recommended in these Guidelines

60. 3. Selecting layer thickness: The selection of trial thicknesses of various layers constituting the pavement should be based on the designers experience And subjected to the minimum thicknesses recommended in these Guidelines and in other relevant specifications 4. Structural Analysis of the selected pavement structure: The analysis shall be done by running the IITPAVE software or Software developed by DoR using the layer thicknesses

61. 5. Computing the allowable strains/ stresses: The allowable strains in the bituminous layer and sub-grade for the selected design traffic are to be estimated using the fatigue and rutting performance (limiting strain) models given in these guidelines. For estimating the limiting tensile strain in the CTB layer, the elastic modulus of the CTB material is an input. 6. Doing the iterations: A few iterations may be required by changing the layer thicknesses until the strains computed by IITPAVE software or Software developed by DoR are less than the allowable strains derived from performance models . 7. Check for cumulative fatigue damage: Where cementitious bases are used in the pavement, the cumulative fatigue damage analysis is required to be done as done in the case of rigid pavement design to make sure that the cumulative proportion of damage caused by the expected axle load spectrum does not exceed unity .

62. 8. Minimum Thickness: The minimum thicknesses, as specified in the guidelines, shall be provided to ensure intended functional requirement of the layer.