非共面复合加载条件下桶形基础稳定性研究

采用荷载-位移联合搜索方法，对于饱和软黏土地基上裙板式桶形基础在水平荷载H、力矩M与扭矩T的非共面复合加载条件下的稳定性进行了比较系统的三维有限元分析，主要探讨了在不同荷载空间内桶形基础的破坏包络轨迹。在分析中，地基土服从基于Tresca屈服准则的理想弹塑性本构关系。计算结果表明，与传统共面复合加载情况相比，非共面复合加载条件下桶形基础的破坏包络面形状有较大差异。非共面复合加载情况下，包络面形状不依赖于基础埋深比，可用简单的圆或椭圆方程进行描述。根据有限元计算结果，将已有的三自由度破坏包络面方程扩展到六自由度复合加载空间内，进而初步建议了一个六自由度破坏包络面方程，并对于实际工程中常用的桶形基础埋深比，给出了方程中偏心度参数取值的确定方法。该方程可用来合理评价复杂荷载条件下软黏土地基上桶形基础承载力。

Stability of bucket foundations under non-coplanar combined loading

Using combined load-displacement searching method, the stability of skirted bucket foundations in saturated soft clay subjected to horizontal load (H), moment (M) and torque (T) non-coplanar combined loading is studied through three-dimensional finite element numerical analysis. The soft soil is assumed to be undrained and obeys elasto-perfectly plastic constitutive relationship following the Tresca failure criterion. The failure locus of bucket foundations in various loading spaces is investigated. The results show that the shape of failure envelopes of bucket foundations subjected to non-coplanar combined loading varies considerably from that under planar combined loading. Under non-coplanar combined loading, the shape of failure envelope does not depend on the aspect ratio of bucket foundations, which may be approximated as a circle or ellipse in normalized load space. Based on finite element analysis, the existing equation of failure envelope in three-degree-of-freedom loading condition is extended to the six-degree-of-freedom case, then an equation of failure envelope involving all six-degrees-of-freedom is suggested, which can be used to evaluate the bearing capacity of bucket foundations in soft soil under combined loading condition. Values of the eccentricity parameter in the proposed equation are also presented for a range of practical embedment ratios.