极端波浪条件下黏土质斜坡海床稳定性解析

Stability analysis of clayey sloping seabed under extreme wave loads

海洋资源开发引起海底软黏土的结构性破坏,导致土体强度弱化,在百年一遇的极端波浪作用时极易发生斜坡海床的局部失稳甚至大范围海底滑坡,给海洋工程建设和正常运营带来严重影响。目前,主要采用极限平衡法评价这类海底斜坡,但该法只能给出近似解。基于极限分析上限方法,推导了极端波浪诱发的波压力对斜坡海床的做功功率,建立了外力功与内能耗散率平衡方程;利用最优化方法,结合数值积分和强度折减技术,求解了不同时刻的斜坡海床稳定性系数,并针对扰动后的斜坡海床开展了有限元解的对比验证。在此基础上,深入探讨了不同波浪参数(波长、波高和水深)和坡长小于一个波长等极端条件下的海底斜坡稳定性。

The shear strength of soft clay in sloping seabed will be weakened due to the structure failure induced by marine resource exploration. Under extreme wave loads once a hundred years,local slide or even large-scale landslide will happen in the seabed. This will influence greatly the construction and normal operation of ocean engineering. Currently,the limit equilibrium method（ LEM） has been one of the most popular approaches to assess the whole or local stability of clayey sloping seabed. But the method has some limitations and only the approximate solutions can be obtained. Based on the upper bound approach of limit analysis,the paper derives the external work rates produced by the wave-induced pressure on the sloping seabed. The limit state equation of sloping seabed under wave loading is established through the external work rates being equal to the internal energy dissipation rates along the log-spiral sliding surface. The factors of safety（ FS） at the different time under one-wave period are obtained by using the optimization method combined with numerical integration and strength reduction technique. A representative example is employed,and the analytical solutions of stability for the disturbed sloping seabed under wave loading are verified by comparison of the finite element results. On this basis,the stability of clayey sloping seabed under extreme conditions such as various wave parameters（ i. e.,wave length,wave height and water depth） and the special case of slope length no more than one wave length are discussed in detail.