基于CD三轴试验的非饱和黄土吸应力强度参数确定

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

非饱和土强度参数的确定是其能够用于工程实际的关键。目前公认的非饱和土强度理论有Bishop的单变量理论、Fredlund的双变量理论以及Lu Ning的吸应力强度理论。其中吸应力强度理论基于吸应力特征曲线,可直接由常规三轴试验得出,回避了测定基质吸力的问题,便于在工程实际中推广。本文通过不同含水率的三轴CD试验,测得陕西泾阳原状Q2(L5)黄土的有效强度参数。结果表明,该黄土不同含水率的有效内摩擦角基本接近;有效黏聚力随含水率的增大呈指数递减,当含水率超过塑限时,黏聚力趋于定值。根据有效黏聚力和吸应力的关系,可以获得吸应力和含水率的关系,即吸应力特征曲线,并通过拟合得出吸应力函数,以及非饱和土强度表达式。

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 thewater 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.