ABSTRACT: Determining the shear strength envelope of an unsaturated
soil involves a sophisticated and time-consuming testing
program. Hence, it is advantageous to minimize the number of tests
required to establish the envelope. In this paper, a power additive
function is adopted to predict the shear strength envelope of unsaturated
soils from knowledge of the unsaturated shear strength at
residual suction, the effective stress friction angle for saturated conditions,
and the soil-water characteristic curve. Two boundary conditions
are required to quantify the two fitting parameters of the
function. The first is b 0 at residual suction, and the second is
the contribution of matric suction to the shear strength at residual
suction, which should be experimentally evaluated. The validity of
the method is tested for a number of unsaturated shear strength data
covering a wide range of suctions. Good agreement was found to
exist between the predicted envelopes and the experimental data.
The method requires only one experimental evaluation of the unsaturated
shear strength and is most suitable for coarse- to mediumgrained
soils where the residual suction may be achieved reliably in
the laboratory.
