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.
