破坏包络面理论在多基础系统中的应用研究

由多个分离基础组成的多基础系统是常用的海洋结构基础型式。基于破坏包络面理论，分析了砂土地基多基础系统的失效模式，建立了相应的承载力计算方法，并验证了计算方法的可行性。对比分析了单一基础和多基础系统不同荷载路径下的荷载安全系数，探讨了破坏包络面理论与分项系数法相结合的基础承载力计算方法。失效模式的分析表明，由于水平荷载的增大，四腿平台结构迎浪侧基础首先到达破坏包络线，其失效模式属于滑动失稳，但由于基础间的运动约束，其并不会出现真正的滑移破坏。随着水平荷载进一步地增大，迎浪侧基础承担的水平和竖向荷载不断减小，导致背浪侧基础受到不断增大的荷载。最终，背浪侧基础也到达破坏包络线，多基础系统失效。分析表明，荷载路径对基础的荷载安全系数有决定性的影响，计算基础的荷载安全系数需指明相应的荷载路径。鉴于破坏包络面的大小和形状取决于众多因素，基础设计时需采用特定工况下的破坏包络面进行承载力计算。

Application of failure envelope theory to multi-footings system

Multi-footing system composed of multiple separate footings is a common type of offshore foundation. Based on failure envelope theory, the failure mode of multi-footing system on sand is analyzed in this study. Additionally, the corresponding analytical method of the bearing capacity is established and its feasibility is verified. The comparison of the calculated load safety factors between the single footing and multi-footing system is conducted in different loading paths. The analytical method of foundation bearing capacity is also conducted based on the combination of the failure envelope theory and partial factor method. From the analysis of failure mode, head sea side footings with four-legged platform firstly reach the failure envelope as result of increasing horizontal load, and their failure modes further become sliding. However, the sliding of head sea side footings would not occur due to the constraints among other footings. Since the head sea side footings bear less horizontal and vertical loads with increasing the horizontal load, the back wave side footings have to undertake larger load. At last, back wave side footings also reach the failure envelope, which results in the failure of the multi-footing system. It is shown that load paths have critical influence on load safety factors, and thus they should be specified when calculating load safety factors. Since the size and shape of failure envelope depend on a variety of factors, the calculation of bearing capacity needs to consider the failure envelope under particular conditions during design of foundations.