浅埋地铁车站的抗液化上浮改进措施数值分析

在强震中,位于饱和可液化地基中的地铁车站会因土层液化而发生上浮灾害,已有的抗液化上浮措施都具备一定减小结构上浮的效果,但仍有改进的空间。本文采用FE-FD耦合方法,分析了在地铁车站周围设置钢板桩截断墙、碎石土排水层及改进的截断墙和改进的碎石排水层措施的地震上浮响应情况,对比了各措施的抗上浮效果,并分析了其工作机理。结果表明:在地铁车站周围设置碎石土层和截断墙的方式都能在一定程度上抑制地铁车站上浮,其中改进的碎石土层和改进的截断墙措施的抗上浮效果都要优于其同类别的方式。改进碎石土层措施主要是通过抑制土层的超孔隙水压力累积来起到抗上浮的作用,而设置改进截断墙方法是通过抑制土体液化后的流动变形来减小结构的上浮。在这两种改进措施中,改进的截断墙方式在不同地震强度作用下其抗上浮效果都更明显,但结构加速度响应的放大效应显著。此外,这两种改进措施对结构的最大剪力和最大弯矩影响较小,但会削弱地铁站结构中柱的最大轴力,这对结构的抗震是有利的。

Numerical Analysis of Anti-liquefaction Uplift of A ShallowBuried Subway Station in Improved Countermeasures

The subway station deposited in the saturated liquefiable soil will suffer from uplift disaster due to soil liquefaction in a strong earthquake. The existing methods for anti-liquefaction uplift can reduce the uplift displacement of the structure, but still need improvement. A finite element and finite difference (FE-FD) coupled method was used in this paper to analyze the uplift response of the subway station with steel sheet piles, with gravelly soil around the structure, and with their improved countermeasures, respectively. The performance of the four countermeasures were compared, and their working mechanisms were discussed. The results show that the uplift of the subway station could be controlled to some extent using the four methods, whereas the two improved countermeasures were better than corresponding original methods. The working mechanism of the improved gravelly soil method is that it can restrain the accumulation of excess pore water pressure, and further control the uplift response of the subway station. In contrast, with the improved steel sheet pile method the flow deformation of the liquefied soils can be controlled to reduce the uplift displacement. In these two improved methods, the anti-liquefaction uplift performances of the improved steel sheet pile method are better under different earthquake densities, but its amplification effect on the acceleration of subway station is more evident. In addition, these two improved methods have a little effect on the maximum shear force and maximum moment of structure during earthquakes, whereas they can reduce the maximum axial force of center pillar of structure, which is beneficial to anti-seismic of the subway station.