Effect of Suction on the Shear Strength of the Decomposed Granite Soil

Decomposed granite soil is widely distributed in the western part of Japan. It is well known that many slope failures of the decomposed granite soil often occur during or after rainfalls. One cause of such slope failure is attributable to a decrease in shear strength due to submergence. It is necessary to investigate the strength characteristics of the partly saturated decomposed granite soil for the slope stability analysis in more detail. The increase in strength of such sandy soil due to the decrease of saturation is caused by changes in suction, frictional characteristics and particle-crushing effect. This paper reports the effect of suction on the shear strength of the partly saturated decomposed granite soil mainly, using the results of the triaxial compression test under the relatively low confining pressure. As the result, a clear agreement was obtained between the increment of the shear strength observed and the incremental shear strength due to the suction with a decrease of saturation.