上软下硬地层隧道掌子面稳定性及塌方形态

为分析上软下硬地层对新奥法施工隧道稳定性的影响,定义掌子面软弱地层相对厚度系数无量纲参数;应用有限元模拟和强度折减相结合的方法,研究不同相对厚度系数下隧道掌子面的稳定性及其塌方形态。结果表明:软硬地层分界线在掌子面中,软弱地层相对厚度系数越大,稳定性越小;随着软弱地层相对厚度系数的增大,掌子面前方塌方范围扩大,最大位移在掌子面软弱地层中心偏下位置,应力拱的范围在扩大,且传递到掌子面下部的力更大,因此更应注重掌子面下部的加固。黏聚力和内摩擦角对掌子面稳定性的共同影响存在最优路径,沿此路径加固效果最为有效;掌子面稳定性随土体重度、开挖高度和掌子面软弱地层厚度的增大而减小;覆跨比对掌子面稳定性影响存在极值,以此作为确定隧道合理埋深的参考条件之一;地表超载只在浅埋情况下才影响掌子面的稳定性。

Tunnel Face Stability and Collapse Shape in Upper-Soft and Lower-Hard Strata

In order to analyze the influence of the upper-soft and lower-hard strata on the stability of the tunnel constructed by the New Austrian Tunneling Method,the dimensionless parameter of the relative thickness coefficient of the weak strata at tunnel face was defined.By means of finite element simulation combined with strength reduction method,the tunnel face stability and collapse shapes under different relative thickness coefficients were studied.Results show that,if the boundary between soft and hard strata is in tunnel face,the greater the thickness coefficient of weak strata is,the smaller the stability is.With the increase of the relative thickness coefficient of weak strata,the area of collapse in front of tunnel face is enlarged and the maximum displacement is below the center of the weak strata of tunnel face.The range of stress arch is expanding,and the force transferred to the lower part of tunnel face is greater.Therefore,more attention should be paid to reinforcing the lower part of tunnel face.There is an optimal path for the joint effect of cohesion and internal friction angle on the tunnel face stability,and the reinforcement effect along this path is the most effective.Tunnel face stability decreases with the increase of soil weight,excavation height and the thickness of weak strata.There is an extreme value for the effect of thickness span ratio on the stability of tunnel face,which can be used as one of the reference conditions for determining the reasonable buried depth of tunnel.Surface surcharge affects the stability of tunnel face only when it is shallow buried.