复合加载条件下沉箱基础稳定性的三维效应

联合采用swipe加载模式与固定位移比加载模式，对于吸力式沉箱基础在水平荷载H与力矩M的复合加载条件下的稳定性进行比较系统的三维有限元分析，主要探讨了基础埋深与直径之比、地基土不排水强度的非均质性对于基础在H-M荷载空间内的破坏包络轨迹的影响，揭示了地基在不同荷载分量组合条件下的失稳破坏机制，并与平面应变假定下得到的结果进行了比较。计算结果表明：平面应变与三维情况下基础的破坏包络面形状有较大差异，分析基础稳定性时，必须考虑其三维效应。在三维情况下，非均质土中埋深与直径之比较小的基础的破坏包络面仍然会向负方向倾斜，已有的包络面方程明显高估这种情况下沉箱基础在正向水平荷载与力矩联合作用下的承载力，从而导致基础设计偏于不安全。

Three dimensional effect on stability of suction caisson under combined loading

Combined with swipe loading method and fixed displacement ratio method, the bearing capacity of suction caisson foundations subjected to horizontal and moment combined loading is explored through three dimensional finite element numerical studies. The effect of embedment to diameter ratio and soil strength nonhomogeneity on the H-M failure envelope of caisson foundations is investigated; and the soil deformation mechanism under various combinations of load components is shown. Through comparison with results under plane strain assumption, it is shown that the shape of failure envelopes of caisson foundations considering three dimensional effect varies from that under plane strain assumption; therefore to evaluate the stability of caisson foundation should account for the three dimensional effect. For nonhomogeneous soil, the failure envelope of caisson foundations with shallower embedment is negatively oblique. The equation of failure envelope available overestimates significantly the bearing capacity of caisson under this condition subjected to positive lateral and moment combined loading, and leads design of caisson foundation to unsafe side.