Determining shear strength of an unsaturated soil by the direct shear tests

Abstract

 Shear strength of an unsaturated soil has a huge effect on the stability of a soil structure. When the soils became more unsaturated with more increased in matric suction, the shear strength of the soils increase which make the stability factor increasing. The research in determining the shear strength of the unsaturated soils has an important and necessary mean. This paper represents the method of determining shear strength of some unsaturated soils in VietNam by the direct shear tests. The results show that the matric suction increases when the soil changes from saturated state to unsaturated one, angle of internal friction, f', of the soil is nearly constant but the cohesion of the soil increases. The angel f^b is equal to f' if matric suction is zero, then the angel f^b decreases. The shear strength of the soils increase which make the factor of safety of the earth dam increasing.