Analysis and design of geosynthetics reinforced unpaved roads on clay subgrades

Abstract

A new non linear approach to analysis and design of unreinforced and reinforced unpaved roads on clay subgrade is developed. These are based on the non-linear stress strain behaviour generally exhibited hy the clay suhgrade soils as well as geosynthetic and natural f1hre reinforcing elements. The newly developed design method is based on closed form solution of the plane strain analysis of the deformation track produced under wheel loading, which consider the compatibility of deformation (rutting) between the constituent materials, clay subgrade and reinforcing element. Appropriate constitutive laws, for montonic and repeated loading conditions, for the subgrade clay and reinforcing elements are developed and used to predict the behaviour under quasi-static and traffic loading conditions. The equivalent material approach is used to simulate the weakening of the system under traffic loading condition. Special test set up are fabricated and installed to estahlish these constitutive relations. The settlement behaviour of clay subgrade is analysed using the fundamental approach suggested by Prakash, Sharan and Saran (1984), using non-linear constitutive relation. The out of the plane load deformation behaviour of reinforcing elements are determined by assuming the deformation track to be of parabolic shape. Design charts are produced to show the applicability of the new methodology for a silty clay subgrade and a woven tape polypropylene geotextile reinforcing element. A comparison of the proposed method with the conventional Giroud and Noiray (1981) method is also produced which show the latter method to yield unsafe results specially under low deformation (rutting) conditions.