Variation of Shear Strength of Unsaturated Weathered Granite Soil with Degree of Saturation and Disturbance at Dongrae, Inje and Yeonki sites

This study investigates the effects of degree of saturation (or water content) and disturbance on the strength reduction for both disturbed and undisturbed samples of weathered granite soil using direct shear test. Several series of direct shear tests were carried out on undisturbed or disturbed samples with 5 different degrees of saturation ranging from 0 to 100%. The direct test results showed that the values of cohesion reduction ratio (CRR) of weathered granite soil were in the range of 45 - 82 %, while the values of friction angle reduction ratio (FRR) in the range of 6 - 11%. Apparent cohesion and friction angle of weathered granite soils also decreased with an increase in degree of saturation. The results indicated that shear strength of unsaturated weathered granite soil at Dongrae, Inje and Yeonki sites tends to reduce due to an increase of water content induced from rainfall infiltration and/or due to disturbance of soil structure.