高孔压作用下海底边坡中麻坑和液化机理研究

A submarine landslide is initiated when the downwards driving stress exceeds the resisting stress of the seafloor slope material causing movements along one or more concave to planar rupture surfaces. Understanding triggering mechanisms of submarine landslides is of great importance in view of the high risk they cause to human beings and facilities in the sea. The purpose of the project is to examine the triggering mechanism of pockmark and liquefaction in low permeability ocean sediment involving high pore pressures associated with gas hydrate dissociation through centrifuge modeling and analytical study. Two failure mechanisms of the low permeability sediment when subjected to high excess pore pressures are highlighted in the study: (1) Tensile failure results in major pockmarks in gentle slopes and thick clays where accumulation of high pore pressure can be up to 2.2 times of the vertical effective stress of the sediment. The failed mass will be intact and showed low mobility. (2) Fractures forming in steep slopes or thin clay layers during its downward movement reduce the amplitude of the accumulated pore pressures to close to or less than the vertical effective stress of soil. The failed mass may liquefy and attain high velocity due to mixing with water. The effects of water salinity, geological strata and inclination of slopes on the mechanism of submarine landslides have also been examined in terms of laboratory tests, physcial and numerical simulation.

海底滑坡是海床在自重或其他荷载作用下发生沿一个或多个滑裂面产生的运动，由于其对海洋工程结构乃至人类生命财产造成重大威胁，因此是海洋工程灾害评估的热点和难点课题，对滑坡机理的分析和滑坡预测都极具挑战性。本项目通过模拟低渗透性土中水合物分解形成的高孔隙压力，开展较系统的离心模型试验和理论分析，旨在揭示含高孔压海床滑坡中两种典型的破坏机理、形成条件及影响因素，即（1）揭示平缓海床中，水合物分解形成的超静孔隙压力达到土体有效竖向应力的2倍以上，导致海床中常见的麻坑（pockmark）现象及以抗拉为主的破坏机理，解释破坏后土体保持原状结构的原因。（2）揭示较陡海床中的裂缝发生机制，及在超静孔隙水压力作用下以剪切为主的破坏机理，解释破坏后土体液化、呈现高流动性，滑坡源附近土体结构完全丧失的原因。同时基于室内材料试验、物理和数值模拟研究海洋环境，如海水高盐度、地层条件、边坡坡度等，对海底滑坡机理的影响。

本项目通过模拟低渗透性土中水合物分解形成的高孔隙压力效应，开展较系统的离心模型试验和理论分析，研究了含高孔压海床滑坡中两种典型的破坏机理、形成条件及影响因素，（1）揭示了含水合物海床常见的麻坑（pockmark）现象及以抗拉为主的破坏机理，解释了破坏土体保持原状结构的原因。（2）揭示了含孔压水下边坡发生液化、具有高流动性，以剪切为主的破坏机理，解释了滑坡源附近土体结构完全丧失的原因。（3）基于无网格的物质点（MPM）方法，开展了海底滑坡过程的模拟，初步揭示滑坡流动性。