Study on the Influence of Small Spacing Tunnel Portal Construction on the Stability of Side Slope Based on Strength Reduction
Relying on highway tunnels in Wuxi-Zhenping expressway,the parameters of tunnel surrounding rock are reduced by strength reduction method.FLAC3D 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.
highway tunnelsmall net distancestrength reduction,entrance constructionside slope stability
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