Abstract：It is proven that shear strength of unsaturated soil increases as increase of matric suction. However，the mechanism of variation of the shear strength with matric suction isn¢t very clear by now. There are two different types of equation in the shear strength theory of unsaturated soils mechanics，one-stress-state-variable equation and two-stress-state-variable equation. Many practical shear strength equations have been established on the base of the two different types of equations. In order to compare different shear strength equations of unsaturated soil，Luojiashan soil samples are selected for the soil-water characteristic curve(SWCC) test and unsaturated triaxial tests. Based on the tests，the air entry value of Luojiashan soil is 237.7 kPa and the residual water content is 4%. It is shown that，with low suction，the triaxial strength of unsaturated Luojiashan soil is directly proportional to suction. These results certify the applicability of two-stress-state-variable strength theory for unsaturated soil. The triaxial shear coefficient φb for Luojiashan soil is 20.7°. The precisions of the previous equations aren¢t satisfied and further research is needed. With the development of unsaturated soil mechanics，researches on the application of shear strength theory of unsaturated soil should be strengthened.
