双层黏土地基方形桩靴贯入过程与穿透机制

采用基于耦合欧拉拉格朗日算法的三维大变形有限元方法对上硬下软黏土地基方形桩靴的贯入过程进行数值模拟，系统地探讨了上下土层强度之比、上层土厚度、土体重度及静止侧压力系数等指标对于桩靴贯入阻力曲线的影响，揭示了穿透现象发生时的土体变形机理。计算结果表明：上下土层强度之比与上层土厚度对于桩靴的贯入阻力曲线具有很大影响。静止侧压力系数的减小在一定程度上导致桩靴承载力系数的降低，而上下土层重度的差异导致桩靴的承载力系数不满足前人建议的方程。在上下土层重度差异不大以及上层土厚度确定的情况下，关于桩靴宽度、上层土重度与强度的无量纲化参数小于临界值时将会发生穿透现象。

Analysis of penetration and punch-through failure of square spudcan in two-layered clays

Based on three-dimensional large deformation finite element method utilizing coupled Eulerian-Lagrangian algorithm, the penetration responses of square spudcan in strong over soft clays were numerically simulated. The effects on the penetration resistance curve were studied of the strength ratio of the bottom clay layer to the top clay layer, the relative thickness of the top layer, the unit weight of soil, and the coefficient of earth pressure at rest. The soil deformation mechanism of punch-through failure during penetration was investigated. The results show that the strength ratio of the bottom clay layer to the top clay layer and the relative thickness of the top layer significantly affects the penetration resistance of square spudcan footings. The peak bearing capacity factor of square spudcan decreases somewhat with the decrease of the coefficient of earth pressure at rest. The penetration resistance curve does not obey the available equation proposed by other authors due to the possible difference of unit weight of the top layer and the bottom layer. The square spudcan footings experience punch-through failure when the proposed dimensional parameter in terms of footing width, the unit weight and undrained strength of upper soil is less than a critical value in the condition that the thickness of upper clay layer is defined and the difference of unit weight of the layers is not appreciable.