近断层强地震动下双层竖向重叠地铁隧道的地震反应

由于近断层地震动的特性显著地不同于距断层较远的地震动,基于江苏省的地震环境和南京地铁的建设背景,以深软场地中的双层竖向重叠隧道结构为研究对象,将地基土-地铁隧道体系视为平面应变问题,以软件ABAQUS为计算平台,考虑土体和隧道混凝土的非线性特性,研究了近断层强地震动作用下地铁双层隧道的水平向非线性地震反应特性,并与单层隧道的地震反应进行了比较。结果表明:在近断层地震动作用下,存在地铁隧道外侧的动应力大于隧道内侧的情况,且隧道的动应力比南京人工波(模拟距离断层较远的中远距离地震动)中震、大震作用下的动应力大1.4～3.4倍;双层隧道上、下两层隧道的动应力幅值均比其对应位置处的单层隧道小;双层隧道的相对水平位移均比其对应位置处的单层隧道大,双层隧道上层顶部的相对水平位移是浅埋单层隧道的1.29～1.69倍;双层隧道底部的加速度反应时程曲线与浅埋或深埋单层隧道的区别不大,其峰值加速度的差异在10%以内。

Seismic Response of Vertically Double-layered Metro Tunnels under Near-fault Strong Ground Motion

As the characteristics of near-fault ground motion differs from those of the distant-fault one re- markably,a set of vertically double-layered metro tunnels in deep soft sites is investigated according to the seismic environment of Jiangsu province and the background of Nanjing metro project.By using the finite- element software ABAQUS,the system of soil-metro tunnels is idealized as a plane strain problem to mod- el the nonlinear dynamic interaction of the system.The stress,displacement and acceleration of the dou hie-layered metro tunnels are calculated respectively to be compared with those of a single-layer tunnel. Results prove that:the phenomenon that the stress on the outside-edge of the tunnel-wall is larger than that on the inside-edge is prevalent under near-fauh strong ground motion,and the stress is 1.4～3.4 times larger than that under moderate and strong Nanjing artificial earthquake waves.The dynamic stress of the double-layered tunnels is lower than that of the single-layer tunnel at corresponding positions while the horizontal relative displacement of the former is larger than that of the latter;and the horizontal rela- tive displacement at the top of the upper tunnel is 1.29～1.69 times as large as that of shallow buried sin- gle-layer tunnel.The acceleration at the bottom of the double-layered tunnels is more or less the same as that of shallow or deep buried single-layer tunnels,and their differences are within the limit of 10%.