Shear Strength Characteristics of Unsaturated Sandy Soil and Mechanisum of Unsaturated Steep Slope Failure

Abstract

In order to examine shear strength of unsaturated sandy soil, unsaturated triaxial tests on 3 kinds of sandy soil were carried out, and some analysis were also carried out based on the results. The shear strength characteristics of unsaturated sandy soil are mentioned below.
(1) Internal friction angle is constant even if suction changes.
(2) Cohesion added by suction is proportional to logarithm of suction (pF).
(3) Because linear relation exists between pF and moisture ratio, Cohesion added by suction is proportional to moisture ratio.
Based on these results, stability of plain sliding slope composed by unsaturated sandy soil is examined. The results are that critical slope gradient becomes smaller in proportion with moisture ratio and drop of critical slope gradient becomes higher as the decrease of cohesion added by suction becomes larger.