黄土隧道洞口浅埋段塌方冒顶处治及效果分析

Treatment and Effect Analysis of Collapse and Roof Fall in Shallow Buried Loess Tunnel Entrance

针对十天高速公路某黄土隧道左线出口发生塌方冒顶事故的处治工程,分析隧道发生塌方冒顶的主要原因,提出采用小导管注浆加固围岩、洞内与地表共同治理的综合处治措施,并结合塌方段原设计初期支护强度不足的工程实际提出了3种初期支护方案;利用数值分析软件FLAC 3D,对3种初期支护方案下隧道在开挖过程中围岩及支护结构的受力和变形情况进行分析。结果表明:采用工况1(I25a型钢钢架+厚30 cm喷射混凝土)初期支护体系刚度偏大,初期支护承载力存在富余,工况3(I20a型钢钢架+厚25 cm喷射混凝土)初期支护体系刚度偏小,为了保证隧道施工安全,并考虑到施工成本,应采用工况2(I22a型钢钢架+厚28cm喷射混凝土)初期支护体系;现场监测数据表明,经过处治后隧道变形较小,最大拱顶沉降为16.4 mm,最大拱顶沉降速率为2.2 mm·d^(-1),最大周边收敛为11.3 mm,最大周边收敛速率为1.6 mm·d^(-1),且最大地表沉降为46.6 mm,相关变化值都在标准范围内,说明处治效果良好;研究结果可为黄土隧道塌方冒顶的预防与处治提供借鉴。

Aiming at the treatment project of the collapse and roof fall accident at the left exit of a loess tunnel on the Shitian expressway,the influence factors of the collapse and roof fall in the tunnel were analyzed.Such comprehensive treatment measures as small pipe grouting for strengthening the surrounding rock,treatment inside tunnel and surface treatment were put forward,and according to the engineering practice that the initial support strength is insufficient,three initial support schemes were designed.Aiming at the three initial support schemes,the stress and deformation of the surrounding rock and supporting structure during tunnel excavation were analyzed by large numerical analysis software FLAC 3D.The results show that the initial supporting system stiffness under working condition 1(I25a steel frame+30 cm thick shotcrete)is relatively large,and the initial supporting capacity is surplus.The initial supporting system stiffness under working condition 3(I20a steel frame+25 cm thick shotcrete)is small.In order to ensure the safety of tunnel construction and take into account the construction cost,the initial support system under working condition 2(I22a steel frame+28 cm thick shotcrete)should be adopted.The field measured data show that after the treatment,the tunnel deformation is small and the maximum crown settlement is 16.4 mm,the maximum crown settlement rate is 2.2 mm·d^(-1),the maximum peripheral convergence is 11.3 mm,the maximum peripheral convergence rate is 1.6 mm·d^(-1),and the maximum ground settlement is 46.6 mm.All the relevant change values are within the standard range,revealing that the treatment effect is good.The research results can provide a reference for prevention and treatment of collapse and roof fall of loess tunnel.