COMPARATIVE STUDY OF FLEXIBLE AND RIGID PAVEMENTS FOR DIFFERENT SOIL AND TRAFFIC CONDITIONS

Abstract

The design and cost of pavements depends on many factors. Two of the most important design parameters are strength of subgrade soil and traffic. The strength of soil subgrade is important because it is this layer which ultimately bears the traffic load. Therefore, the thickness of the upper layers is dependent on its strength as the traffic load should reach the subgrade within the allowable limits of its strength. On the other hand, pavements are designed to carry traffic loading and to provide smooth riding surface for traffic. Depending on the intensity of the traffic the thicknesses of the different layers in a pavement differ. There are generally two types of pavements, flexible and rigid. Each of these pavement types use the soil and traffic design inputs in different forms. In the first part of this study, mathematical models are developed which help convert a traffic load given in one format (say msa) into another format (say ALD) or vice-versa. Using these models it is possible to get the axle load distribution (ALD) from individual vehicular counts. It is observed that different vehicle classes follow typical axle load distribution of their own and these distributions do not show significant change over time. In the second part of the study, flexible pavements have been designed for different soil and traffic conditions and their cost of construction and maintenance have been computed. The Indian guidelines for the design of flexible pavements, IRC: 37 (2001) requires that the soil strength be measured in terms of CBR and traffic loading in terms of million standard axles. A total of 90 pavements were designed and costs computed for. A mathematical relationship is developed to express the cost of flexible pavements in terms of CBR and msa.