湛江结构性黏土在三维应力下的力学特性与强度准则

Mechanical properties and strength criterion of Zhanjiang structured clay in three-dimensional stress state

为了探究湛江结构性黏土在三维应力状态下的力学特性以及结构性对其强度准则的影响,开展了一系列不排水条件下不同中主应力比b值等平均主应力p真三轴试验和平面应变试验。结果表明:p小于与大于结构屈服应力,整体上广义剪应力q-大主应变ε_(1)曲线分别呈现为应变软化型与轻度应变硬化型;不同b值下的q-ε_(1)曲线形态相近,但随b值增加,峰值点q对应的大主应变呈现减小的规律;且有效黏聚力随着b值增大而减小,有效摩擦角随b值增大而增大,平面应变试验有效黏聚力和摩擦角的值则介于b=0.25和b=0.50对应的有效黏聚力和摩擦角之间;受结构性的影响,湛江黏土在π面上的强度准则在p值小于结构屈服应力时接近于Lade-Duncan准则,而在p值大于结构屈服应力时更加接近基于Mises准则和Lade-Duncan准则的广义非线性强度理论;平面应变试验结果表明,湛江黏土在平面应变加卸载条件下破坏时的b值在0.18~0.29之间,破坏时的强度可以用基于广义Mises与Lade-Duncan平面应变强度准则的广义平面应变强度准则近似估计。

In order to investigate the mechanical properties of Zhanjiang structured clay in the three-dimensional stress state and the influence of structure on its strength criterion, a series of undrained true triaxial tests of different intermediate principal stress ratios,b-values, with equal mean principal stress, p-values, and undrained plane strain tests was carried out. The results are as follows. When p is less than or greater than the yield stress of the structure, the q-ε_(1) curves are strain softening and mild strain hardening type in general. The q-ε_(1) curves of true triaxial tests with different b-values are similar in shape. As b-value increases, the large principal strain corresponding to the q peak point shows the decreasing trend. Under different b-values, the effective cohesion decreases with increasing b-values, while the effective friction angle increases with increasing b-values. The effective cohesion and friction angle for the plane strain compression tests are between the effective cohesion and friction angle corresponding to b=0.25 and b=0.50.Influenced by the structure of clay, the strength criterion on π plane is applicable to the Lade-Duncan criterion when p-values are less than the yield stress of structure, while it is more applicable to the generalized nonlinear strength theory based on Mises criterion and Lade-Duncan criterion when p-values are greater than the yield stress of structure. For plane strain tests, the b-values of Zhanjiang clay under plane strain loading and unloading conditions are between 0.18 and 0.29 at failure, and the strength at failure can be approximated by the generalized plane strain strength criterion based on the general Mises and Lade-Duncan plane strain strength criterion.