考虑孔隙水渗流和孔隙重分布的地震场地液化后变形特性研究

Liquefaction-induced ground failure was recognized as a major cause of damages during earthquakes. The post-liquefaction deformation process of ground is associated with seepage flow of pore water, void redistribution and stress adjustment during diffusion and dissipation of the excess pore pressures. However, most of the current studies of soil liquefaction are assumed to be undrained condition, in which the drainage condition of actual site and the seepage flow of pore water are not considered. Such effect on post-liquefaction behaviour of ground has not been clear and few researches pay attention to this issue. In this application, we will take the effect of void redistribution as well as the seepage flow of pore water as the key scientific issue for clarifying the mechanism of liquefaction-induced ground deformation. Based on comprehensive research approaches including material tests, physical model test, numerical simulation and theoretical analysis, the emphasis of this project is on (1) clarifying the variation of soil property parameters at low effective stresses, such as soil permeability as well as the compressibility properties of the liquefied sand; (2)exploring the mechanism of post-liquefaction deformation of ground taking the natural drained conditon and the seepage flow of pore water into account; (3) investigating the characteristics of void redistribution and its effect on the post-liquefaction behaviour of ground in liquefied multi-layer site. On the basis of above mentioned, we will then carry out the mechanism of liquefaction-induced large deformation or lateral flow of ground associated with seepage flow of pore water and void redistribution. The results from this project will offer an imperative background for developing mitigation techniques against liquefaction-induced geo-disaster.

地震液化是导致众多岩土工程震害的主要原因之一，液化后土体变形的过程是伴随超孔压扩散和消散，存在孔隙水渗流、孔隙重分布和应力不断调整的过程，而目前关于液化问题的研究大多假定为不排水条件，对于场地实际排水条件以及孔隙水渗流对液化后土体变形的影响一直没有得到充分认识。基于此，本项目紧紧围绕孔隙水渗流和孔隙重分布对液化后土体变形特性的影响机制这一关键科学问题，采用室内试样试验、物理模拟与数值试验和理论分析相结合的研究方法，通过探索创新试验方法和试验测试技术，针对低有效应力状态下土性参数变化规律及其与超孔压关联性、自然排水和孔隙水渗流条件下液化后土体的受力变形特性、多层场地液化后土体孔隙重分布特征和变形演化规律等方面开展深入研究，进一步揭示考虑孔隙水渗流和孔隙重分布影响的地震场地液化后大变形或流滑失稳破坏机理。研究成果将为防治液化引起的岩土工程震害提供科学依据。

我国是一个地震多发国家，震后引起的饱和砂土液化问题是岩土工程界研究的热点与难点之一。液化后土体变形的过程是伴随超孔压扩散和消散，存在孔隙水渗流和应力不断调整的过程，而目前相关研究大多假定为不排水条件，对于场地实际排水条件对液化后土体变形的影响一直没有得到充分认识。因此，本项目采用室内试样试验、物理模拟和理论分析相结合的研究方法，针对低有效应力状态下土性参数变化规律及其与超孔压关联性、自然排水条件下液化后土体的受力变形特性、多层场地液化后土体变形等方面开展深入研究，主要结论如下：. （1）以土体重固结理论和砂沸机理为基础，研制了一套可测定饱和砂土处于低有效应力状态下的渗透系数的渗透试验装置，并对该装置的使用方法及试验步骤做了详细说明。. （2）开展了三种不同颗粒级配的砂土在低有效应力状态下的渗透特性试验，试验结果表明：三种试验土样的渗透系数均在低有效应力状态下，渗透系数增大明显，其中3#砂变化最大，其渗透系数为液化前的4倍左右；1#砂增幅次之，为液化前的2.5倍左右；2#砂增幅最小，为液化前1.5倍左右。. （3）设计了可控制渗透系数大小的排水夹层装置，该装置放置在试样顶部，实现了对试样不同排水条件的控制。. （4）开展了不同排水条件下饱和砂土动三轴试验，获得了不同排水条件下饱和砂土试样的超孔隙水压发展和应力-应变关系曲线。试验结果表明：饱和砂土试样超孔隙水压随着渗透系数比降低而增大。试验条件下，渗透系数比小于0.54时试样液化而大于0.54时饱和砂土试样不能液化。. （5）开展了饱和砂土试样液化后剪切试验，获得了液化后饱和砂土试样在不同排水条件下的超孔隙水压力消散和变形曲线。试验结果表明：液化后饱和砂土试样的剪切模量随着渗透系数比的增大而增大，相应液化后试样体积剪缩量减小，而剪切吸水效应增强，试样抗剪强度折减率增大。