三轴试验中基于外衬塑布裂缝的偏应力计算

在常规三轴固结排水剪（CD）试验中,按照规范整理得到了(σ1~σ3)~εa曲线和εv~εa曲线，但发现由这两条曲线确定的临界状态点不一致，不符合经典临界状态的定义。通过试验过程中试样外衬塑布的裂缝分布情况确定了试样的剪切破坏面，得出试样破坏面与试样中心轴的交点位置随围压的变化规律，对计算截面面积A_b的公式进行了推导，提出了偏应力计算取值的新方法。按照新方法计算了εv~εa和(σ′1－σ3)~εa 曲线，且由该曲线确定的临界状态点趋于一致， 符合土体达到临界状态时的宏观力学现象。

Deviatoric stress calculation of triaxial test based on crack of outside-wrapped plastic cloth

In CD test of conventional triaxial test, we have obtained the(σ1~σ3)~εa andεv~εa curves according to the specification, however, the critical state points of the two curves are not consistent with each other, which does not conform to the classical definition of critical state. The damage plane of test samples were studied through the cracks distribution of the plastic cloth wrapped the sample during the test process, and the relationship between the damage point, an intersection point of damage plane and the sample central axis, and the confining pressure are analyzed. The calculation formula of section area Ab is derived, a new method for deviatoric stress calculation is put forward. The curves of(σ1~σ3)~εa andεv~εa are calculated by the new method, and the critical state points of the new curves tend to be uniform, which conforms to the soil macroscopic mechanics phenomenon at critical state．