含倾斜砂土夹层的人工岛地震液化灾害分析

Analyses of seismic liquefaction induced disaster in artificial island with sloping sand layer

强地震易造成地基中倾斜砂土夹层液化后产生永久变形和位移,并诱发流滑现象,进而对上部结构产生严重破坏.基于FE-FD耦合有限元方法,综合考虑倾斜砂土夹层的坡度、厚度、埋深以及海水水位因素,对某近海人工岛二维结构模型进行了数值模拟分析.结果表明:砂土层的坡度、厚度、埋深以及水位因素对人工岛的地震液化灾害有着不同程度的影响,其中坡度的影响最显著,而水位的影响最不明显,特别是水位对超孔隙水压力增长的影响非常小.人工岛的侧向扩展是在地震过程中饱和倾斜砂土夹层完全液化被触发后才得以发生,而且是在地震作用过程中某段时间内沿液化层斜面的有限滑动,其灾害程度比水平砂土层液化造成的破坏要大得多,而且易造成岛体不均匀沉降,对护岸造成严重破坏.该分析结论可为近海岸工程地震液化灾害评价分析提供参考依据.

Liquefaction due to strong earthquake easily causes permanent displacement and strain of sloping sand layer in the fundament and induces the phenomena of flow slides,and then brings serious damages to the superstructure. Considering sloping sand layers＇ gradient, thickness, depth and seawater level synthetically, a two-dimensional offshore artificial island model was simulated numerically by FE-FD coupling finite element analysis method.The experimental results indicate that these four influence factors have different effects on the large deformation of artificial island in the course of seismic liquefaction.The influence of gradient is the greatest,and the influence of seawater level is the most non-obvious,and especially,its effect on excess pore water pressure is very small. Lateral spreading of artificial island j ust occurs after total liquefaction of saturated sloping sand layer in the course of seismic,which is a limit slide along the slope during a period of time.Its degree of damage is much bigger than that of damage induced by liquefaction of horizontal sand layer,and it easily causes serious differential settlement and damage of revetment of artificial island. These analytical results can provide reference for hazard evaluation of offshore engineering due to seismic liquefaction.