饱和黄土隧道围岩地震液化特征的振动台试验研究

Shaking table tests on seismic liquefaction characteristics of soil surrounding tunnels in saturated loess stratum

以兰合铁路某在建隧道为工程背景,对其黄土段开展了1∶20大比例尺饱和黄土围岩地震液化的系列振动台试验,揭示了土-结构相互作用对隧道衬砌周围土体液化势的影响规律。研究结果表明:土-结构相互作用显著提高了隧道衬砌周围土体的液化势,当遭遇地震荷载时,围岩会先于同一水平地层土体而产生液化;激励地震加速度a_(max)的较小时(a_(max)=1.0 m/s^(2)),同一水平高度靠近衬砌结构土体的动剪应力峰值ι_(d,maxt)、动孔隙水压力峰值d,U_(max)、和加速度峰值a_(p,max)都要比远离衬砌结构的大,具有明显的放大效应;随着激励地震加速度a_(max)的增大至接近围岩液化阶段时,动孔隙水压力U_(d)的放大效应明显,而剪应力ι_(d,maxt)和加速度a_(p,max)的放大效应减小或者消失。同时上述结果中围岩土体加速度的变化特征,揭示了前期相关数值分析研究存在的不足。

Based on the previous numerical and theoretical analyses,a series of shaking table tests with scale of 1∶20 for seismic liquefaction analysis of saturated surrounding loess are carried out to simulate the loess section of a tunnel under construction on the Lanzhou-Hezuo Railway in China.The results show that the soil–structure interaction significantly increases the liquefaction potential of the soil near the tunnel linings,and the surrounding soil will produce liquefaction before the soil of the same level when subjected to seismic loads.When the peak acceleration of seismic loads a_(max) is minor(i.e.,a_(max)=1.0 m/s^(2)),the peaks of dynamic shear stress ι_(d,maxt),dynamic pore water pressure d,U_(max),and acceleration a_(p,max) near the lining structure are larger than those far away from the lining at the same level height,and have obvious amplification effects.With the increase of a_(max) to near the liquefaction stage of surrounding soil,the amplifying effects of dynamic pore water pressure U_(d) are obvious,while the amplifying effects of shear stress ι_(d,maxt)and acceleration a_(p,max) decreases or disappear.In particular,the variation characteristics of the acceleration of the surrounding soil reveal the deficiency of the previous numerical simulations.