非饱和土强度公式的比较研究

 非饱和土力学的基本理论已经确认了基质吸力的存在有利于非饱和土的强度提高，但是对于强度提高的机制到目前为止没有统一的结论，非饱和土强度理论中存在着单应力状态变量公式和双应力状态变量公式2种基本的理论表达式，并在此基础上产生了许多实用的强度公式。通过珞珈山土样的土–水特征曲线试验和非饱和三轴剪切试验对非饱和土强度公式进行比较研究。结果表明，珞珈山土样的进气值和残余含水量分别为237.7 kPa和4%；珞珈山土样非饱和强度在低吸力范围内，与吸力基本成线性增长关系，验证了非饱和土双变量强度公式的适用性；珞珈山土样的非饱和抗剪强度参数约为20.7°；现有的非饱和土实用公式精确性较差，非饱和土抗剪强度理论的应用有待进一步的研究与完善。

RESEARCH ON COMPARISON OF STRENGTH EQUATIONS OF UNSATURATED SOIL

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.