基于Lade-Duncan准则的平面应变强度公式

Soil strength equation under plane strain condition based on Lade-Duncan criterion

在弹性-理想塑性和相关联流动法则的假设下,基于Lade-Duncan准则,得到了平面应变破坏的中主应力条件,提出一种新的平面应变条件下的强度公式。该公式将平面应变条件和常规三轴压缩条件下的抗剪强度指标联系起来,只须通过常规三轴试验,就可确定平面应变条件下的内摩擦角和黏聚力,可以有效反映中主应力对平面应变内摩擦角的提高效应。证明了等效内摩擦角达到极大值的条件即为平面应变条件下无黏性土的破坏条件,以及绘制π平面上3种准则的几何关系,阐明平面应变强度公式的数学意义。最后,通过地基承载力试验结果验证了该公式的有效性。在使用规范方法或有限元软件进行平面应变计算时,该公式可考虑中主应力的影响,选取更为有效的抗剪强度指标。

According to the elastic-ideal plastic assumption and associated flow rule,the intermediate principal stress equation and the strength equation in plane strain condition are proposed on the basis of Lade-Duncan criterion.The shear strength parameter under plane strain condition is connected with that under conventional triaxial condition.Therefore,the equivalent internal friction angle and the cohesion in plane strain condition can be determined by a conventional triaxial test,which can effectively reflect the effect of intermediate principal stress on the increase of internal friction angle under plane strain condition.It is proved that the friction angle at the condition of strength failure of non-cohesive soil under plane strain is that of the maximum value of the equivalent friction angle,which is the mathematical meaning of the new strength equation.The mathematical meaning of the new strength equation is also shown by drawing the geometric relationship of three criteria on theπplane.The effectiveness of the strength equation is confirmed with experimental results of bearing capacity.In the calculation of plane strain using the standard method or the finite element method,the new strength equation can choose shear strength parameter more efficiently,considering the influence of the intermediate principal stress.