INVESTIGATION OF PRFSSURE DISTRIBUTION PROPERTY OF DIFFERENT BASE COURSE: MATERIALS WITIT VARVI`G WHEEL LOADS

Abstract

one of the principal problems in the structural design of flexible pavement has been the determination of the minimum thickness of granular base and surfacing„ The mean emphasis in design analysis is placed on the prevention of any subgrade failure under specified wheel load conditions. Several design methods are in practice but upto this date there is no universally accepted formula for determining the minimum thickness of flexible pavements that should be placed on a given subgrade to support the specified wheel load. The existing metho]s, with the exception of those based on soil strength tests viz., plate bearing tests and penetration tests, do not consider the factor of pavement material quality in the thickness analysis. It is imperative to study the effectiveness of various base course materials and their influence on the design of flexible pavements. The load distribution property of various base course materials, if investigated, may indict cats the degree of the effectiveness with which an individual material under the specified loading condition and the thickness may behave as a strnct,.ral c ponent of t ;o p v ;;;t layers. Herner(l 9 2) has reported the results based on this approach by conducting the tests on pavement materials of thicknesses greater than 8 inches. In the discussion of the work by Horner 2), C.W. Johnson pointed out that the 2 phenomenon needs further investigations on the thicknesses lower than 8 inches, since it is not realistic to assume the behaviour of thin layers similar to thick layers . It is proposed to investigate the effectiveness of an individual base course material by conducting load transmission tests, which may consist in recording the pressures on the subgrade under the applied surface loads. Further the investigations proposed is with the static loads to approach the problem from a simple to a complex aspect. A model study may be desirable and economical. The object . of the present investigation. would be to determine the transmission and distribution of the applied surface loads through the base course:.. By conducting load transmission tests, it appears possible to observe, measure and graphically represent the resulting behaviour of the materials, and the magnitude .and distribution of subgrade reaction, for given conditions of loading, thickness and type of base courses. A collection of the test data over a wide range of base terse types and thicknesses may provide a basis to compare the efficiency of the several, types in practice. Such results may also help towards the achi.eve. merit of a realistic design procedure for flexible av ments'= If the subgrade supporting capacity and an allowable limiting deflection can be determined from the tests and pavement performance studies, it may be possible to assign the subgrade K a rating in terms of the surface load per unit area. With the known load transmission characteristics of the pavement sections, it would be possible to determine the needed pavement thickness under the given loading condition for the subgrade rating. It is intended to conduct tests on the .types of the base course materials which are commonly used in different parts of India.