DETERMINATION OF SUCTION STRESS STRENGTH PARAMETERS OF UNSATURATED LOESS WITH CONVENTIONAL TRIAXIAL CD TEST

The study on strength theory of unsaturated soil and the determination of related parameters are the core of the research in unsaturated soil mechanics. At present, Bishop's single-variable strength theory, Fredlund's double-variables strength theory, and Lu Ning's suction stress strength theory are generally accepted. Lu Ning introduced the concept of suction stress and the suction stress characteristic curve(the relationship between the suction stress and the volumetric water content).This theory avoids the determination of matric suction and it is convenient for widely promotion in engineering practice. This paper tests the effective strength parameters based on the conventional triaxial CD test with different water contents. Results show that the effective internal friction angles with different water contents are basically same. The effective cohesion increases with the water content. When the water content increases to the plastic water content, the cohesion reaches a constant value. According to the relationship between effective cohesion and the stress suction, suction stress characteristic curve can be obtained and then fit the stress suction function. The function can explain unsaturated strength combined with the effective internal friction angle and saturated effective cohesion.