ESTIMATION OF THE UNSATURATED SHEAR STRENGTH CURVE FOR WEATHERED GRANITIC SOILS

The shear strength parameters of a soil are the most essential properties affecting the stability of soil structures. These parameters are generally measured in the laboratory with undisturbed samples. However, it may also be necessary to estimate these parameters from relevant soil behaviors. In this study, the equation proposed by Vanapalli et al. was applied for estimating shear strength curves for some weathered granitic soils in Korea. Two methods for estimating the shear strength curve of unsaturated soils were proposed by Vanapalli et al. One method uses the fitting parameter, k, based on the volumetric water content(VWC) of the soil water characteristic curve(SWCC) and some unsaturated shear strength values obtained at several metric suction levels. The other method estimates the shear strength curve of unsaturated soils by the residual water content of SWCC. The first method has higher accuracy but the experimental procedure is more complicated. In this study, the second method was applied for domestic weathered granitic soils. The residual water content were calculated using 10 SWCC's obtained from previously published test results, and each shear strength curve of unsaturated soils were obtained. The metric suction range was from 1 to 400 kPa, and the data were compared with the data from the previous study. The results show that the second method also has a reasonable accuracy for domestic weathered granitic soils. It is suggested that, in case it is difficult to measure the unsaturated shear strength curve through the triaxial soil tests, the method using residual water content can be a useful alternative to obtain the unsaturated shear strength curve.