中文摘要：

港口、海洋工程结构物基础一般处于复合加载状态，其极限承载力通常采用近来引入的极限荷载图进行评价。对位于地基表面的重力式海洋基础，需要考虑基础与地基间的接触特性对极限承载力的影响。以大型通用有限元软件ABAQUS为计算平台，建立了复合加载模式的地基极限承载力数值分析方法；针对饱和黏土地基上的表面基础，利用在ABAQUS平台上开发的接触计算模块，模拟基础与地基间竖向可分离、切向完全粘结的接触作用；进而基于建立的分析方法，进行系统的有限元计算，分析地基的破坏模式随荷载条件的变化，给出地基的极限荷载包络图，并与经典承载力计算公式结果进行对比。研究结果表明，经典承载力计算公式低估了三维荷载条件下的地基极限承载力，有限元计算模型及数值分析方法，可以较好地分析研究地基的失稳机理及承载力特性，并可考虑基础与地基不同的接触条件对破坏模式及组合极限承载力的影响。

英文摘要：

Foundations of harbor and offshore engineering structures are often subjected to combined loads. Recently, the bearing capacity of this kind of foundations is evaluated by failure envelop. As for the gravity offshore foundations on the surface of subsoil, the effect of footing/ soil interactive behavior on the bearing capacity must be considered. Based on the commercial finite-element method package ABAQUS, numerical analysis procedures are established for calculating the bearing capacity of foundation under combined loading. For the surface footing on clayed subsoil, the interactive behavior between footing and soil is generalized as zero-tension in normal conditions and full adhesion at tangent, and simulated using the user＇ s subroutine ceded within the framework of ABAQUS. Based on the suggested procedure, finite element calculations have been performed systematically. According to the calculation, the failure mechanisms varying with loading conditions are investigated, and failure envelops are presented and compared to envelops from the traditional formulae. The study shows that the traditional formulae under- estimate the limit bearing capacity of foundations under three dimensional loads, and the failure locus obtained via finite element analysis pro- rides benchmark solutions for design of offshore foundations.