砂土液化大变形的弹塑性循环本构模型

A cyclic elasto-plastic constitutive model for evaluating large liquefaction-induced deformation of sand

循环剪切过程中饱和砂土的3个体积应变分量(有效球应力变化引起的体变、剪切引起的可逆性体变和不可逆性体变)的变化规律决定了液化后剪应变的发展。基于上述机理、对剪切引起的可逆性和不可逆性体变的数学描述、体积相容性条件以及边界面本构理论框架,建立了一个可描述饱和砂土液化后大变形的弹塑性循环本构模型。通过对饱和砂土排水和不排水循环扭剪试验结果的模拟表明,该模型不仅可以合理地模拟饱和砂土循环加载条件下从液化前到液化后、从小剪应变到大剪应变的变形发展过程,而且可以合理地模拟饱和砂土液化后再固结大体变的累积特性。本文的研究为定量描述砂土液化后大变形提供了一条合理而有效的途径。

The post-liquefaction shear strain of saturated sand subjected to cyclic loading was found to be governed by the changes of the three volumetric strain components, i.e., a component induced by the variation in the mean effective confining stress, a reversible dilatancy component and an irreversible dilatancy component. Then a new cyclic elasto-plastic constitutive model for saturated sand were established, based on the following four important aspects： ① the above-mentioned new mechanism; ② a new mathematical description of the two dilatancy components; ③ consistent condition that the three volumetric strain components must meet for various conditions of drainage; ④ the theoretical frame of bounding surface plasticity. The model had been preliminarily confirmed to be effective through various comparisons between the calculated and tested results for Toyoura sand. It was shown that the presented model could be used well, not only to simulate the development of shear strain from a small to large range during an entire pre- and post-liquefaction process, but also to evaluate the accumulation process of large volumetric strain induced in post-liquefaction reconsolidation. The present study provided a rational and effective approach to evaluate the large liquefaction-induced deformation quantitatively.