可液化地层中盾构施工诱发振动影响的数值模拟研究

Numerical simulation of vibration induced by shield tunneling in liquefiable ground

以太原市地铁2号线人民南路站~化章街站区间可液化地层盾构施工过程中遇到地表沉降超限问题为例,采用FLAC3D有限差分软件,进行盾构隧道施工过程模拟,在开挖面水平方向模拟盾构施工振动的正弦速度边界,进行动力响应分析,分析孔压比、超静孔隙水压力、加速度时程曲线。分析结果表明:盾构机掘进太原市复合地层在隧道上覆黏质粉土及粉细砂层中形成一定液化区域,上覆土层中开挖面前方液化区域面积明显大于开挖面后方液化面积;盾构隧道轴线对应地表沉降最大值达60mm,与现场实测值相同,最大沉降发生在开挖面前方1m处;超静孔隙水压力在液化土层中形成一旋涡区,漩涡中心靠近液化层底部,位于开挖面前方,超静孔隙水压力在漩涡区中心最大,向四周扩散逐渐减小。本文的研究成果对盾构在可液化地层中的施工有一定参考价值。

During the construction of liquefiable ground shield tunneling between Renmin South Road Station and Huazhang Street Station of Metro Line 2 in Taiyuan,the problem of surface subsidence exceeding the limit is encountered.In order to study the disturbance of shield-induced vibration to liquefiable strata,FLAC3D finite difference software is used to simulate the construction process of shield tunnel in this paper.The sinusoidal velocity boundary simulating the vibration of shield construction is applied in the horizontal direction of the excavation face,then dynamic response analysis is carried out,including pore pressure ratio,excess pore water pressure and acceleration time history curve.The analysis results show that:a certain liquefaction area is formed in the clayey silt and fine sand layer over the shield tunneling in Taiyuan,and the liquefaction area in the overlying layer before excavation is obviously larger than the liquefaction area behind the excavation face.The maximum surface settlement corresponding to the axis of shield tunnel is 60mm,which is the same as the measured value in the field.The maximum settlement occurs at 1m in front of the excavation.The excess pore water pressure forms a vortex area in the liquefied soil layer,and the center of the vortex is near the bottom of the liquefied layer,just before the displacement excavation.The excess pore water pressure reaches the maximum in the vortex area,and its diffusion decreases gradually in the periphery.The research results of this paper have certain reference value for shield construction in liquefiable stratum.