天然软黏土屈服面及流动法则试验研究

Experimental study on the yield surface and flow rule of natural clays

天然沉积的软黏土往往具有结构性和塑性各向异性，通过对K固结温州软黏土的19组三轴排水应力路径试验和4组三轴不排水剪切试验的研究，揭示典型结构性软黏土的屈服特性和屈服后的塑性流动特征。试验研究表明在各种三轴应力路径下，天然软黏土的应力应变曲线均表现出明显的结构屈服特征和塑性各向异性。典型的天然结构性软黏土的初始屈服面在p’～q平面上呈现出倾斜椭圆的形状，可以采用Wheeler等建议的屈服面方程描述，而屈服后塑性流动方向基本符合正交流动法则。同时对温州软黏土在较大等向应力作用下屈服面的旋转作了试验研究，试验结果揭示了该过程中原有的塑性各向异性逐渐消失、土体呈现出塑性各向同性性状的规律，表明天然软黏土具有明显的旋转硬化规律，而后继塑性变形符合正交流动法则。

Structure and anisotropic plasticity are the essential nature of naturally deposited soft clays. Nineteen diffferent stress probe tests and four undrained triaxial tests on K0-consolidated Wenzhou clay are analyzed, and the yield surface as well as plastic flow rule beyond yielding also studied. The test results of various tiaxial stess paths show that the stess-strain curves of natural soft clay are characterized by structural yielding and anisotropic plasticity. The initial yield surface of natural soft clay can be described by an inclined ellipse on the p＇ - q plane based on the yield function proposed by Wheeler et al （2003） , and the normality law is approximatively used for describing the flow behavior. The rotational behavior of yield surface is also studied under relatively high isotropic stress condition through another group stress probe tests of Whenzhou clay. The test results show that the initial anisotropy gradually disappears along with isotropization during the test, and such behavior can be explained by the rotational hardening theory of soft clay.