IRC:SP-72-2015 GUIDELINES FOR THE DESIGN OF FLEXIBLE PAVEMENTS FOR LOW VOLUME RURAL ROADS (First Revision) Published by: INDIAN ROADS CONGRESS Kama Koti Marg, Sector-6, R.K. Puram, New Delhi-110 022 June, 2015 Price : `??? (Plus Packing & Postage) IRC:SP-72-2015 First Published : June, 2007 First Revision : June, 2015 (All Rights Reserved. No part of this publication shall be reproduced, translated or transmitted in any form or by any means without the permission of the Indian Roads Congress) Printed by India Offset Press, Delhi- 110 064 1000 Copies IRC:SP-72-2015 Contents S. No. Description Page No. Personnel of the Highways Specifications and Standards Committee i - ii 1. Introduction 1 2. The Design Process 5 3. Traffic Parameter 8 4 Subgrade Strength Evaluation 15 5 Pavement Composition and Maximising use of Locally Available Materials 19 6. Pavement Design of Gravel/Soil-Aggregate Roads 24 7 Design of Flexible Pavement for Traffic over 1,00,000 Cumulative ESAL Repetitions 26 8. Recommended Pavement Designs 30 9. Drainage and Shoulders 3 6 References 36 Appendix A 37 Appendix B 38 Appendix C 39 Appendix D IRC:SP-72-2015 PERSONNEL OF THE HIGHWAYS SPECIFICATIONS AND STANDARDS COMMITTEE (As on 12th January, 2015) 1. Das, S.N. Director General (Road Development) & (Convenor) Special Secretary to Govt. of India, Ministry of Road Transport & Highways, New Delhi. 2. (Co-Convenor) Addl. Director General, Ministry of Road Transport & Highways, New Delhi. 3. Prasad, Vishnu Shankar Chief Engineer (R) S,R&T, Ministry of Road (Member-Secretary) Transport & Highways, New Delhi. Members 4. Basu, S.B. Chief Engineer (Retd.), MORTH, New Delhi 5. Bongirwar, P.L. Advisor, L & T, Mumbai 6. Bose, Dr. Sunil Head, FPC Divn. CRRI (Retd.), Faridabad 7. Duhsaka, Vanlal Chief Engineer, PWD (Highways), Aizwal (Mizoram) 8. Gangopadhyay, Dr. S. Director, Central Road Research Institute, New Delhi 9. Gupta, D.P. DG (RD) & AS (Retd.), MORTH, New Delhi 10. Jain, R.K. Chief Engineer (Retd.), Haryana PWD, Sonipat 11. Jain, N.S. Chief Engineer (Retd.), MORTH, New Delhi 12. Jain, Dr. S.S. Professor & Coordinator, Centre of Transportation Engg., Dept. of Civil Engg., IIT Roorkee, Roorkee 13. Kadiyali, Dr. L.R. Chief Executive, L.R. Kadiyali & Associates, New Delhi 14. Kumar, Ashok Chief Engineer (Retd.), MORTH, New Delhi 15. Kurian, Jose Chief Engineer, DTTDC Ltd., New Delhi 16. Kumar, Mahesh Engineer-in-Chief, Haryana PWD, Chandigarh 17. Kumar, Satander Ex-Scientist, CRRI, New Delhi 18. Lal, Chaman Director (Project-III), NRRDA (Ministry of Rural Development), New Delhi 19. Manchanda, R.K. Consultant, Intercontinental Consultants and Technocrats Pvt. Ltd., New Delhi 20. Marwah, S.K. Addl. Director General, (Retd.), MORTH, New Delhi 21. Pandey, R.K. Chief Engineer (Planning), MORTH, New Delhi i IRC:SP-72-2015 22. Pateriya, Dr. I.K. Director (Tech.), NRRDA, (Ministry of Rural Development), New Delhi 23. Pradhan, B.C. Chief Engineer (NH), PWD, Bhubaneswar 24. Prasad, D.N. Chief Engineer (NH), RCD, Patna 25. Rao, P.J. Consulting Engineer, Faridabad 26. Raju, Dr. G.V.S. Engineer-in-Chief (R&B), Rural Roads, Director Research and Consultancy, Hyderabad 27. Representative of BRO (Shri B.B. Lal), ADGBR, HQ DGBR, New Delhi 28. Sarkar, Dr. P.K. Professor, Deptt. of Transport Planning, School of Planning & Architecture, New Delhi 29. Sharma, Arun Kumar CEO (Highways), GMR Highways Limited, Bangalore 30. Sharma, M.P. Member (Technical), NHAI, New Delhi 31. Sharma, S.C. DG (RD) & AS (Retd.), MORTH, New Delhi 32. Sinha, A.V. DG (RD) & SS (Retd.), MORTH, New Delhi 33. Singh, B.N. Member (Projects), NHAI, New Delhi 34. Singh, Nirmal Jit DG (RD) & SS (Retd.), MORTH, New Delhi 35. Vasava, S.B. Chief Engineer & Addl. Secretary (Panchayat) Roads & Building Dept., Gandhinagar 36. Yadav, Dr. V.K. Addl. Director General (Retd.), DGBR, New Delhi 37. The Chief Engineer (Mech.) (Shri Kaushik Basu), MORTH, New Delhi Corresponding Members 1. Bhattacharya, C.C. DG (RD) & AS (Retd.), MORTH, New Delhi 2. Das, Dr. Animesh Professor, IIT, Kanpur 3. Justo, Dr. C.E.G. Emeritus Fellow, 334, 14th Main, 25th Cross, Banashankari 2nd Stage, Bangalore 4. Momin, S.S. Former Secretary, PWD Maharashtra, Mumbai 5. Pandey, Dr. B.B. Advisor, IIT Kharagpur, Kharagpur Ex-Officio Members 1. President, (Bhowmik, Sunil), Engineer-in-Chief, Indian Roads Congress PWD (R&B), Govt. of Tripura 2. Honorary Treasurer, Indian Roads (Das, S.N.), Director General Congress (Road Development), & Special Secretary to Govt. of India, Ministry of Road Transport & Highways 3. Secretary General, Nahar, Sajjan Singh Indian Roads Congress ii IRC:SP-72-2015 GUIDELINES FOR THE DESIGN OF FLEXIBLE PAVEMENTS FOR LOW VOLUME RURAL ROADS 1 INTRODUCTION 1.1 This document is revision of the IRC:SP:72-2007 “Guidelines for the Design of Flexible Pavements for Low Volume Roads”. The need for the revision arose to include design charts using stabilized base and sub – base courses as also to enable design of rural roads for traffic volume upto 2 MSA. Accordingly, a sub group consisting of Dr. I.K. Pateriya, Dr. Sudhakar Reddy, Dr. UC Sahoo and Shri S.C. Sharma was constituted to consider the proposed revision. This sub-group had several meetings and finalized the draft. The draft revised guidelines were deliberated before the Rural Roads Committee (H-5) in its meeting held on 16th December, 2014 and the modified draft was approved. Thereafter, the modified draft was placed before the Highways Specifications & Standard Committee (HSS) in its meeting held on 16th January, 2015. The HSS Committee approved the modified draft of revised guidelines which was then put up before the IRC Council in its meeting held on 20th January, 2015 at Bhubaneswar. Council authorized the convener of H-5 Committee for incorporating suggestions before publication of the revised guidelines as suggested by the Council. 1.1.1 The personnel of Rural Roads Committee (H-5) are as follows:- Gupta, D.P. -------- Convenor Jain, N.S. -------- Co-Convenor Director (Projects-I), NRRDA -------- Member-Secretary (Solanki, N.C.) Members Banerjee, A.K. Kumar, Dr. Praveen Bongirwar, P.L. Kumar, Dr. Ashok Dushaka, Vanlal Parameswaran, Dr. (Mrs.) Lakshmy Franco, Colin A. Pateriya, Dr. I.K. Goswami, Diganta Raju, Dr. G.V.S. Gupta, Mukesh C. Sagne, A.A. Gupta, S.K. Sarkar, Prof. A.K. Jain, Dr. M.C. Satish, J. Jain, Dr. P.K. Sharma, S.C. Kadiyali, Dr. L.R. Singhvi, S.S. Kalra, B.B. Sun, M.M. Kapaley, A.D. Tongden, C.P. Katare, P.K. 1 IRC:SP-72-2015 Corresponding Members Jawaid, Dr. S.M. Ali Kumar, Vijay Justo, Dr. C.E.G. Reddy, Prof. K. Sudhakar Kand, Dr. C.V. Rohatgi, Rajesh Khanna, Ms. Shobha Ex-Officio Members President, Indian Roads Congress (Bhowmik, Sunil), Engineer-in-Chief, PWD (R&B) Govt. of Tripura Honorary Treasurer, (Das, S.N.), Director General (RD), Ministry of Indian Roads Congress Road Transport & Highways, New Delhi Secretary General, Nahar, Sajjan Singh Indian Roads Congress 1.2 Pre-requisites for suitable and Economical Designs There are a number of important points to be considered while evolving suitable and economical designs for the low-volume rural roads in India. First and foremost is the aspect of practical implementability of the recommended designs within the available resources and level of expertise in rural areas, availability of equipment/plant for construction and maintenance as well as the level of quality control that can be effectively exercised in rural areas. To the extent possible, the use of locally available materials as such or after suitable processing has to be maximized in the larger interest of economy. The design life to be taken for purposes of pavement design should neither be too short to require expensive upgradation/rehabilitation at close intervals nor should it be so long as to require prohibitively high cost of initial construction. Ideally, maintenance considerations should be built into the design e.g. provision of adequate drainage, resistance to soil erosion along side slopes, adequate lateral support from shoulders etc. as would minimize subsequent maintenance requirements. Lastly, the designs should aim at providing the level of serviceability which should not fall below the minimum acceptable level during the design life, essentially amounting to evolving performance-based designs. All these important considerations and international experiences have to be kept in view while working out suitable and economical pavement designs for rural roads. 1.3 Earlier Design Approach (IRC:SP: 20-2002) 1.3.1 In the first edition of IRC:SP:20-2002, Rural Roads Manual (Ref. 1), the traffic parameter for pavement design is evaluated in terms of commercial vehicles per day, grouping together the heavy commercial vehicles like trucks, full-sized buses etc. with the much lighter commercial vehicles like tractors/tractor-trailers, pick-up vans, mini buses, tempos etc. The percentage of laden, unladen and overloaded commercial vehicles has not been considered in the traffic parameter. 1.3.2 The subgrade strength parameter is evaluated in terms of 4-day soaked CBR values except in areas with annual rainfall less than 500 mm and where the water table is 'too deep'. 2 IRC:SP-72-2015 1.3.3 A set of pavement design curves A, B, C and D for traffic categories 0-15, 15-45, 45-150 and 150-450 CVPD have been provided as also design catalogues with minimum base course thickness of 150 mm for Curves A and B and a minimum base course thickness of 225 mm for curves C and D. The sub-base course thicknesses have been arrived at by subtracting the minimum base course thickness from the total pavement thickness requirement, obtained from the pavement design curves. 1.3.4 In regard to the type of surfacing, all rural roads, except those (i) in an arid region with annual rainfall less than 500 mm and traffic upto 150 motorized vehicles per day (except two- wheelers) and (ii) in a region with annual rainfall less than 1000 mm and traffic upto 50 motorized vehicles per day (except two-wheelers) only, need to be provided with a bituminous surface treatment. The design of Unsealed Gravel Roads does not receive a separate treatment in IRC:SP:20-2002 (Ref 1). As a result, practically all rural roads being constructed in the country are black-topped. 1.4 Existing Design Approach (IRC:SP:72- 2007) 1.4.1 For purposes of pavement structural design in this Design Manual, the low volume rural roads are divided into the following categories: Gravel/Aggregate-surfaced roads (Unpaved Roads); Flexible Pavements (Paved Roads); and Rigid Pavements 1.4.2 The international experiences, for the past several decades, with Gravel Roads notably in the USA (Ref 2) show that the 'maximum traffic level upto 100,000 Equivalent Standard Axle Load (ESAL) applications can be considered for Gravel Roads, while the practical minimum level (during a single performance period) is 10,000'. Below ESAL applications of 10,000, even Earth Roads are suitable. Gravel is defined as a mix of stone, sand and fine-sized particles used as a sub-base, base or surfacing on a road, the material specifications for use in these layers being available in Clauses 401 and 402 of the MORD Specifications for Rural Roads. When the required gradation of gravel is not available in a natural form, the blending of naturally occurring materials in the required proportions may be resorted to. 1.4.3 For low volume rural roads, still carrying a sizable volume of truck and bus traffic, the maximum number of ESAL applications considered for flexible or rigid pavement is upto 1 million ESAL applications (Ref 2). The practical minimum traffic level for a flexible or rigid pavement is about 50,000 ESAL applications during a single performance period (Ref 2). 1.4.4 The pavement designs presented in the Manual for both, Gravel and Flexible Pavements (the rigid pavement designs are dealt with separately) are performance-based, drawing on the extensive experiences in the USA on Low Volume Road Design, as brought out in the AASHTO Guide for Design of Pavement Structures (Ref 2). The Serviceability rating system from 5 to 1 as per the PMGSY Operations Manual 2005 (in terms of Present Serviceability/Condition Index) (Ref. 3) has been adopted. For the low volume rural roads 3 IRC:SP-72-2015 in India, a 'Terminal Serviceability Index' (i.e, the lowest index that will be tolerated before rehabilitation /strengthening or reconstruction becomes necessary) of 2.0 is considered suitable. The thickness of gravel/aggregate-surface roads (unpaved roads) has been based on the following criteria: (i) the serviceability loss over the design life is limited to 2.0, taking the initial serviceability index to be 4.0 just before opening the road to traffic, and the terminal serviceability of 2.0 when rehabilitation will be due, with or without provision of an overlay. (ii) the allowable depth of rutting under 3 m straight edge does not generally exceed 50 mm. The thickness of flexible pavements (paved roads) has been based on the Structural Number (SN) recommended by AASHTO for low volume roads for those of the US climatic zones which represent the climatic conditions of our country, for a 50% reliability level. 1.4.5 The design traffic parameter has been expressed in terms of the cumulative 80 kN (8.16 tonnes) ESAL applications during the design life. Seasonal variations by way of enhanced traffic during the harvesting seasons have also been considered. 1.4.6 For the evaluation of subgrade strength for new roads, the selection of moisture content has been dealt with scientifically instead of always insisting on 4-day soaked CBR values. For the rehabilitation or upgradation of existing rural roads, the use of Dynamic Cone Penetrometer (DCP) (mm/blow) has also been recommended for insitu subgrade strength evaluation. 1.5 Salient Features of Existing Designs Some of the more important features of the existing designs are as under: • Pavement designs for new roads as well as for the upgradation/rehabilitation of existing roads have been included. • The recommended designs aim at maximizing the use of locally available materials including industrial waste (where possible) • A simple procedure has been detailed for carrying out traffic counts, computing the ADT and the number of ESAL applications during the design life, selected as 10 years. • Categorizing the subgrade strength in 5 classes and classifying the traffic into 7 ranges has simplified the presentation of design catalogues for both gravel roads and flexible pavements. • The warrants for providing a bituminous surface treatment have been spelt out. • The importance of monitoring the long-term performance of rural roads constructed with the recommended designs, by way of periodically carrying out condition, surveys cannot be overemphasized. Systematic condition 4