各向异性软黏土基坑抗隆起稳定极限平衡分析

LIMIT EQUILIBRIUM ANALYSIS ON STABILITY AGAINST BASAL HEAVE OF EXCAVATION IN ANISOTROPY SOFT CLAY

天然黏土表现出明显的强度各向异性,在软黏土地区中的基坑抗隆起分析时有必要考虑土体各向异性的影响。针对桩墙式支护基坑绕下道支撑的圆弧滑动抗隆起稳定模式,采用基于空心圆柱仪(HCA)杭州原状软黏土试验结果的土体强度各向异性不排水强度公式,根据极限平衡法推导得到坑底抗隆起稳定分析公式。结合算例,讨论了土体强度各向异性、挡墙入土深度、最下道支撑和坑底间的距离等因素对坑底抗隆起稳定的影响,比较了该文方法与传统方法结果的差别,指出不考虑土体强度各向异性的软黏土基坑抗隆起分析和基于传统Casagrande各向异性公式的抗隆起分析都将高估杭州软黏土基坑的抗隆起稳定性。最后采用该方法分析杭州某失稳基坑实例,通过与已有方法结果的对比,验证了该文方法的合理性。

As the strength of natural clay shows significant anisotropic properties, it is necessary to consider the effects of the anisotropy of soft clay when analyzing stability against basal heave of excavation. Assuming that the soil slip failure mode is a circular arc sliding mode and its center is at the intersection point of the retaining wall and the lowest support, a formula of the anisotropic clay strength based on the results of Hangzhou intact soft clay tests using hollow cylinder apparatus（HCA）. Limit equilibrium method is adopted in the derivation of the equation of stability against basal heave of excavation. Furthermore, the influence on stability against basal heave of excavation caused by factors such as the anisotropy ratio of soil, the embedded depth of the retaining wall and the distance between the foundation base and the lowest support is discussed. The method proposed in this paper is verified by a case study on Hangzhou soft clay. It is also shown that the safety against basal heave would be overestimated if the anisotropy of strength is ignored or the Casagrande anisotropic strength formula is adopted.