复合地层隧洞中隔离桩对围岩位移的控制效果分析

Control effect on rock displacement by isolation piles in composite stratum tunnel

设置隔离桩作为一种控制城市隧洞开挖引起围岩变形的有效手段,在“上软下硬”复合地层中的作用效果还罕有研究。依托滇中引水工程龙泉隧洞,采用FLAC^(3D)软件,分析隔离桩桩位、桩径、桩长及桩顶埋深等参数对隧洞衬砌及地表建筑物变形控制效果的影响。结果表明:设置隔离桩能够阻隔地层应力的传递,合理的设计参数是充分发挥隔离桩阻隔作用的关键;同等条件下,隔离桩对地层位移的限制作用在水平方向优于竖直方向;隔离桩距离隧洞越近、桩径越大,控制变形效果越好;隔离桩只有穿过地层滑移面并嵌入下层土体时,才能够较好控制由隧洞开挖引起的隧洞衬砌以及地表建筑物位移,建议嵌入下层土体深度为隔离桩长度的1/4;适当设置桩顶埋深能够降低隔离桩对于土体的牵引作用,建议桩顶埋深深度为隔离桩长度的1/5。研究成果可为隔离桩在城市浅埋复合地层隧洞工程中的应用提供参考。

As an effective method to control the deformation of surrounding rock caused by urban tunnel excavation,the effect of isolation pile in"upper soft and lower hard"composite stratum is rarely studied.Based on the Longquan tunnel project of water diversion in central Yunnan Province,FLAC^(3D)software was used to analyze the influence of parameters such as isolation pile position,pile diameter,pile length and pile top buried depth on the deformation control effect of tunnel lining and surface buildings in"upper soft and lower hard"composite stratum.The results show that the isolation pile can block the transmission of formation stress,and reasonable design parameters are the key to give full play to the barrier effect of the isolation pile.Under the same conditions,the limiting effect of the isolation pile on the ground displacement is better in the horizontal direction than that in the vertical direction.The closer the isolation pile is to the tunnel and the larger the pile diameter is,the better the deformation control effect is.The displacement of tunnel lining and surface buildings caused by tunnel excavation can be well controlled only when the isolation pile penetrates through the slip surface of the stratum and is embedded into the lower layer.It is suggested that the depth of embedding lower soil is 1/4 of the pile length.Properly setting the buried depth of the isolation pile top can reduce the traction effect of the isolation pile on the soil.It is suggested that the buried depth of the pile top is 1/5 of the pile length.The research results supplement the effect of isolation piles in composite stratum,which can provide reference for the application of isolation piles in shallow buried composite stratum in cities.