1614145318824_DESIGN OF FLEXIBLE PAVEMENT ppt.pptx

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1. DESIGN OF FLEXIBLE PAVEMENT PRESENTED BY: UNDER THE GUIDANCE OF VIPUL CHAUHAN DR. VANEETA DEVI 50225 ASSISTANT PROFESSOR Dept. Of Civil Engineering Pantnagar

2. INTRODUCTION A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the sub-grade.

3. Pavement design in road construction

4. TYPES OF PAVEMENT Flexible pavement : Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the points of contact in the granular structure. Rigid pavement : Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below.

5. DATA REQUIRED FOR DESIGN OF FLEXIBLE PAVEMENT Indian roads congress has specified the design procedures for flexible pavements based on CBR values. The Pavement designs given in the previous edition IRC: 37-2012 were applicable to design traffic up to only 30 million standard axles ( msa ). The earlier code is empirical in nature which has limitations regarding applicability and extrapolation. These guide lines follow analytical designs and developed new set of designs up to 150 msa in IRC: 37-2018 .  

6. TESTS There are several types of tests which are as follows: CBR Test Sieve Analysis Dry Density Test Bitumen Test

7. CBR TEST DEFINITION OF C.B.R. :- It is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material . C.B.R. = Test load/Standard load X 100 The same samples were further tested for CBR using Static Compaction with 56 blows by standard rammer of 2.6 kg.

8. Sieve Analysis A Sieve Analysis is a procedure to assess the particle size distribution of a granular material by allowing the material to pass through a series of sieve of progessively smaller mesh size.

9. Maximum Dry Density Test Test pits were excavated. Maximum dry density (MDD) corresponding optimum moisture content (OMC) were determined using standard compaction method and modified method in accordance with IS:10074:1987, BIS 270 (Part-VIII ).

10. Bitumen Test The various tests for bitumen are as follows. These tests are common for straight run bitumen and cutbacks. Penetration test. Furol viscosity test. Float test. Kinematic viscosity test. Ductility test. Softening point test. Flash point and fire point test.

11. TYPICAL LAYERS OF FLEXIBLE PAVEMENT

12. DESIGN OF FLEXIBLE PAVEMENT A Flexible Pavement of 750 meters patch is being designed in accordance with the charts in IRC 37-2012. With reference to the Geotechnical tests and traffic survey performed, the important parameters and their values are determined, & on that basis, the design of the pavement is done . Though , the available width is taken as 4.5 meters, in which the carriageway width is taken as 3.7 meters and shoulders on the either side of the road as 1.00 meters, and also the provision of the side drains is made as well.

13. Computation of Design Traffic The design traffic is considered in terms of the cumulative number of standard axles(in the lane carrying maximum traffic) to be carried during the design life of the road. This can be computed using the following equation :- N = 365 x [ (1+r)n – 1] x A x D x F/r Where, N = Cumulative number of Standard axles to be catered in the design in terms of use. A = Initial traffic in the year of completion of construction in terms of the number of commercial vehicles per day . D = Lane distribution factor R = Annual growth rate of commercial vehicles F = Vehicle damage factor N = Design life in years

14. STEPS FOR DESIGN OF FLEXIBLE PAVEMENT A Bituminous Pavement is Considered to be critical/failed when either of the two condition occurs- An average rut depth of 20mm or more, measured along the wheel path has occurred. The occurrence of fatigue cracking (appearing as inter connected cracks), whose total area in the section of the road under consideration is 20 % or more than the paved surface area of the section Cumulative Number of Standard axles required to produce Condition 1 and condition 2 are determined. For good performance of the pavement the cumulative standard axles due to traffic in the design life of the pavement must be less than these values.  

15. PROCEDURE OF DESIGN (Granular and Granular Sub-Base Course) Step 1 - Selecting the Composition. Step 2- Bituminous mix design and estimation of Resilient modulus . For Sub Grade

16. Step 3- Selection of trial thickness Trial thickness is adopted based on the design traffic by virtue of designer’s experience. A catalogue has also been presented in IRC 37 for Traffic ≤ 50 msa . But these are just indicative, proper design is to be conducted for traffic > 2 msa . For Traffic less than 2 msa , IRC SP:72 shall be used. The thickness of these layers must be greater than the minimum thickness requirement laid down by IRC - For Sub base Course – 150 mm when Filter cum Drainage layer is provided, and 100 mm each when Filter and Drainage layer are provided Separately. The thickness of unbound Granular layer shall not be less than 150mm

17. Step 4-Structural Analysis of the pavement Structure Assuming layers to be perfectly elastic (with elastic constant as resilient modulus) analysis is conducted and the governing Stresses/strains at critical location are determined by IITPAVE (not necessarily ). Step 5- Computation of permissible Strains using Equation (3.1/3.2 and 3.2/3.4 ) Step 6-Doing the iterations by changing layer thickness until Step 4 gives strain less than equation (3.1/3.2 and 3.2/3.4).

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