Mechanical Properties of Decomposed Granite Soil under Low Pressures

Slopes of sandy soil such as decomposed granite soil are susceptible to be suffered from damages when they are inundated by rainfalls. One of causes of such shallow slips is attributed to the decreasing of shear strength of the soil due to submergence. Another noteworthy characteristic of this soil is that the particles are easily crushed under a relatively low stress. In order to discuss the shallow slips of decomposed granite soil, it is necessary to investigate the chang in shear characteristics owing to the variation of the water content at low normal stresses. The commonnest strength parameters in use for the stability analyses of the slope are generally obtained from the test at higer normal stresses than the actual stress which applys to the slope. This paper shows the effect of water content on the shear strength characteristics of decomposed granite soil at a very low normal stress in detail on the basis of the direct shear test result, and its comparison with the results of triaxial compression test. As the results of this experiment, we found the uniqe relationship between the shear strength and the degree of saturation at a low normal stress.