强震作用饱和粉土地层盾构隧道碎石桩抗液化技术研究

Research on Anti-liquefaction Technology of Gravel Columns in Shield Tunnel with Saturated Silt under Strong Earthquake

地震作用下饱和粉土地层易出现液化现象,造成地基失效与结构受损。因此,对地震作用下饱和粉土地层地铁盾构隧道抗液化措施的研究具有一定的意义。依托天津地铁5号线典型液化区段,采用数值模拟的方法分析了碎石桩加固前后盾构隧道的位移响应以及饱和粉土地层的抗液化性能。研究结果表明:在0.3 g强震作用下饱和粉土地层2~6 m深度处超孔压比均超过0.65,发生液化现象,同时隧道出现明显的水平位移及竖向位移;设置碎石桩后,各测点超孔压比降低至0.65以下,液化现象消除;采用碎石桩加固后,地基超静孔压明显下降,并在达到峰值后超静孔压出现明显的消散现象;碎石桩桩长对隧道水平位移和竖向位移均有较大影响,增加碎石桩桩长能有效减小隧道的竖向位移和水平位移,而桩长超过15 m后桩长对隧道水平位移的影响不再明显。研究成果可为类似工程提供一定理论依据。

Saturated silt is prone to liquefaction under the action of earthquake,resulting in ground failure and structural damage.Therefore,it is of great significance to study the anti-liquefaction measures of metro shield tunnel in saturated silty soil under earthquake action.Based on the typical liquefaction section of Tianjin Metro Line 5,the displacement response of the tunnel supported by gravel piles and the anti-liquefaction performance of saturated silty soil layer are analyzed by numerical simulation.The research results show that:under the action of 0.3 g earthquake,the over-pore pressure ratio at the depth of 2~6 m of the saturated silty soil layer exceeds 0.65,and liquefaction occurs.At the same time,the tunnel has obvious horizontal displacement and vertical displacement.After the anti-liquefaction measure of stone columns is adopted,the excess pore pressure ratio of each measuring point decreases to below 0.65,and the liquefaction phenomenon is eliminated.After using rock columns,the excess pore pressure of foundation decreases obviously,and dissipates obviously after reaching the peak value.The length of gravel pile has a great influence on the horizontal and vertical displacements of the tunnel.Increasing the length of gravel pile can effectively reduce the vertical and horizontal displacements of the tunnel,but the influence of pile length on the horizontal displacement of the tunnel is no longer obvious when the pile length is more than 15 m.The research results can provide some theoretical basis for similar projects.