ANALYTICAL STUDY FOR DEVELOPMENT OF METHODOLOGY FOR DESIGN OF FLEXIBLE PAVEMENTS

Abstract

Transportation services play an instrumental role in the economic development, development of trade, and social integration of a country which is dependent on conveyance of both people and goods. Transportation demand in India has been growing rapidly. There has been a significant growth in the vehicular traffic over the years and till date, a single pavement section on any National highway in India has not survived its design life. Therefore, there is a need for strong, durable and cost-effective development of highways. The current design practice for pavements in India is based on empirical methods which have many drawbacks and are largely based on experience. Hence, there is need for the development of an analytical method for the design of flexible pavements since this method can overcome the drawbacks of the empirical method. In the analytical method, the composition and thickness of layers are so selected that the stresses, strains and deformations produced by the design traffic loading do not exceed the capabilities of any material in the pavement. The proportions of the pavement are adjusted until an acceptable design results in which all the critical factors are within permissible limits. The critical strains to be kept within the permissible limits are the horizontal tensile strain at the bottom of the bituminous layer under the load axis which is known as fatigue and vertical compressive strain at the top of subgrade under the load axis known as rutting. Since new combinations of pavements have been introduced in the latest pavement design guidelines which consist of cement treated base and cement treated sub-base, tensile strain in cementitious layer is also a new critical strain introduced which needs to kept within permissible limits. In this dissertation work, analytical software IITPAVE which was developed by IIT Kharagpur, India under the research scheme R-56 of Ministry of Road Transport & Highways, India has been used for the design of flexible pavements. The input values required in the software were wheel load, tire pressure, poisson’s ratio, modulus of elasticity and thickness of each layer and the type of tire configuration. Tire pressure of 0.8MPa has been used for analysis. The above values were taken from clauses of IRC:37-2001 and IRC:37-2012. Two combinations of flexible pavement were considered for design. The first combination included the standard case having WMM and GSB along with the bituminous layer and the second combination consisted of cement treated base and cement treated sub-base with aggregate inter layer for crack relief. Under each iv combination, three cases of subgrade CBR, namely 5%, 10% and 15% were chosen for design and for each subgrade CBR, design was carried out for four traffic conditions which are 30 msa, 50 msa, 100 msa and 150 msa. Different combinations of thickness were obtained under each traffic condition by varying the individual layer thickness. Cost analysis was then performed on these thicknesses using rates from Schedule of Rates, PWD Uttarakhand to get the most economical pavement. The limitations of the latest Indian code IRC:37-2012 developed for the design of flexible pavements has also been discussed in this dissertation work.