正常固结黏土中扭矩对负压沉箱承载力的影响分析

当负压沉箱被用作深水管汇或管道终端基础时，除了受到上部结构传来的竖向力、水平力和弯矩，还会受到扭矩，扭矩可能降低沉箱的竖向承载力、水平承载力和抗弯能力。采用理论分析和有限元法研究复合加载条件下典型沉箱（长径比介于1~2之间）与正常固结黏性土的相互作用，考虑安装造成的沉箱侧壁周围土体的弱化，得到了不排水条件下沉箱单向最大扭矩，探索了扭矩与不同荷载分量联合作用时承载能力的改变。结果表明，当扭矩不超过20%的抗扭转能力时，可以忽略扭矩对竖向承载力、水平承载力或抗弯能力的影响；当扭矩介于抗扭转能力的20%~80%时，其他承载力分量最多降低20%。提出了能够用于工程设计的扭矩对其他荷载分量抗力的影响系数。

Influence of torsion on bearing capacity of suction caisson in normally consolidated clay

When suction caissons are used as foundation of the manifold or pipe terminal in deep waters, they are subjected to a torsion except for the vertical force, horizontal force and moment applied. The torsion may reduce the vertical, horizontal and moment bearing capacities of caisson foundation. In this study, theoretical analyses and finite element simulations are conducted to study the interaction between normally consolidated clay and the typical caisson (with a length-to-diameter ratio between 1 and 2) subjected to combined loadings. The strength reduction of the soil around the caisson skirt induced by installation are considered in the theoretical and numerical analyses. For caissons under undrained conditions, the uniaxial torsion capacity and the influences of the torsion on the other capacities are obtained. The results show that when it is less than 20% of the torsional capacity, the torsion applied has slight effect on the vertical, horizontal or moment capacities. When torsion applied reaches 20%~80% of the torsional capacity, the other three capacity components can be reduced by as much as 20%. The torsion influence factors against three capacities are proposed for routine designs.