基于强度折减的小净距隧道洞口施工对边仰坡稳定性影响研究

Study on the Influence of Small Spacing Tunnel Portal Construction on the Stability of Side Slope Based on Strength Reduction

以巫镇高速某公路隧道为背景,通过强度折减法对隧道围岩参数进行折减,采用FLAC 3D有限差分软件对洞口段隧道开挖进行了数值模拟,并基于现场监测对模拟参数进行了标定,分析了隧道洞口施工边仰坡稳定性和极限剪应变分布特征,探明了不同折减系数下隧道洞口段位移变化规律,提出了隧道洞口边仰坡稳定性安全系数合理取值和位移安全基准值。研究结果表明:1)初始状态时,当折减系数介于1.36~1.38时,岩体位移变形速率加快,累计变形量发生突变,边仰坡上方极限应变区域贯通;2)隧道洞口施工后,当折减系数介于1.20~1.22时,岩体位移变形速率加快,累计变形量发生突变,隧道间极限应变区域贯通,故提出隧道施工的洞口边仰坡稳定性安全系数控制基准值为1.2,此时竖向位移安全基准值为80 mm,水平位移安全基准值为35 mm。

Relying on highway tunnels in Wuxi-Zhenping expressway,the parameters of tunnel surrounding rock are reduced by strength reduction method.FLAC 3D finite difference software is used to simulate the excavation of tunnel portal section.The simulation parameters are calibrated based on field monitoring.The stability and ultimate shear strain distribution characteristics of tunnel portal construction slope are analyzed.The displacement variation of tunnel portal section under different reduction coefficients is proved.The reasonable value of safety factor and displacement safety reference value of tunnel portal slope stability are put forward.The results show that:1)In the initial state,when the reduction coefficient is between 1.36 and 1.38,the displacement and deformation rate of rock mass is accelerated,the cumulative deformation is abruptly changed,and the limit strain area above the side slope is connected;2)After the construction of the tunnel portal,when the reduction coefficient is between 1.20 and 1.22,the displacement deformation rate of the rock mass is accelerated,the cumulative deformation is abruptly changed,and the ultimate strain area between the tunnels is penetrated.Therefore,it is proposed that the safety factor control reference value of the slope stability of the tunnel portal is 1.2,and the vertical displacement safety reference value is 80 mm,and the horizontal displacement safety reference value is 35 mm.