矩形隧道支护压力不均对地层稳定影响分析

Effects of non-uniform support pressure on the stability of box tunnel working face

针对矩形隧道施工中难以保持土仓压力,以及矩形隧道掘进机配置的多刀头和双螺旋输送机或三螺旋输送机造成的压力波动会增大隧道面不稳定风险的问题,考虑掘进面未被完全支护的情况,基于筒仓-楔形体模型,通过极限平衡法对地层稳定性进行分析,并引入强度折减法,得出了稳定性安全系数计算式。对土体抗剪强度、隧道埋深和无支护区域大小等因素进行参数分析,结果表明:土体强度参数和隧道几何参数对安全系数影响较大;当未支护比率大于0.75、土体有效内摩擦角小于20°时,安全系数小于1,易发生失稳破坏。最后通过苏州某矩形隧道工程案例,讨论本文解的适用性。

In box tunneling,maintaining support pressure in the working chamber is a challenge.Moreover,the pressure fluctuates due to the box tunnel machine configurations with multiple cutterheads and double or trible screw conveyors.As a result,the fluctuation of support pressure enhances the risk of tunnel face instability.In this paper,a typical situation that the ground was not fully supported against by the pressure at the face was considered and the silo-wedge model was applied to investigate the ground stability.The stability was analyzed through limit equilibrium analysis and the strength reduction method was introduced to derive the solution of safety factor of the ground stability.The parametric analysis was performed to explore the influences of factors such as soil shear strength,cover depth and unsupported area on the ground stability.The results indicate that the stability is significantly influenced by the soil shear strength and unsupported area.When the proportion of unsupported area is larger than 0.75 or the effective internal friction angle of the soil is less than 20°,the working face is under high risk of collapse respecting the calculated safety factor which is below 1.Finally,the case of box tunneling in Suzhou,China is re-examined to discuss the capability of current solution.