超前支护下隧道掌子面稳定性极限上限分析

Upper-bound limit analysis of tunnel face stability under advanced support

软弱围岩隧道施工中,常采用超前支护确保隧道施工的安全。为了评价超前支护下隧道稳定性,建立了超前支护作用下截锥体、对数螺旋线共同破坏模型,基于极限分析上限法和综合强度折减法开考虑初期支护未支护段的影响,推导出了隧道稳定安全系数的目标函数,开利用Matlab编制程序求解该函数以此判断隧道稳定性。与模型试验结果和已有理论研究成果对比分析,验证了计算方法的合理性,同时分析了影响隧道稳定安全系数的各个因素。研究结果表明:围岩黏聚力、内摩擦角的增加,掌子面锚杆、拱部超前支护的施作对提高围岩稳定性有显著的作用,而初期支护未支护段长度、开挖高度的增加不利于围岩的稳定;在围岩内摩擦角较小时,分台阶开挖降低开挖高度提高隧道稳定性的效果更好;在围岩内摩擦角较大时,掌子面锚杆加固强度的增加对隧道稳定性提高的作用更显著。最后给出了超前支护的施工设计建议图,可为工程中初步确定超前支护参数和施工方法提供参考。

Advanced support is often used to ensure the safety of tunnel construction in soft surrounding rock.In order to evaluate the tunnel stability under the advanced support,a joint failure model of truncated cone and logarithmic helix under the advanced support effect was established.The objective function of the tunnel safety factor was deduced based on the limit analysis upper bound method and the comprehensive strength reduction method,and considering the influence of the unsupported section of initial support.The function was solved using Matlab programming to judge the tunnel stability.Compared with model test results and existing theoretical research results,the rationality of the proposed method was verified,meanwhile,the factors affecting the safety factor of the tunnel stability were also analyzed.The research results show that with increasing the soil cohesion and internal friction angle,the applications of tunnel face bolt and arch pre-consolidation measures have a significant effect on the stability of the surrounding rock,while the increase of unsupported length and excavation height is not conducive to the stability of surrounding rock.When the internal friction angle is small,it is more beneficial to improve the stability of tunnel to reduce the excavation height by bench method.The increase of reinforcement strength of bolt in the working face plays a more significant role in improving tunnel stability.Finally,the construction design proposal drawing of the advanced support was given,which can provide a reference for the preliminary determination of the advanced support parameters and construction methods.