高地应力软岩隧道超前导洞扩挖施工过程受力变形分析

Analysis of stress and deformation of soft rock tunnel with high ground stress in pilot heading expansion

超前导洞法是开挖隧道前在所在断面提前施作小导洞从而释放应力的一种方法。本文研究导洞完成后圆孔扩挖过程中隧道内各层支护的受力变形。以兰渝铁路木寨岭隧道岭脊段为研究对象,从实际工程布设测点获取数据,进行超前导洞应力释放效果分析、圆形扩挖施工各层变形分析、圆形扩挖先后行隧道施工相互影响分析,以及长锚杆和锚索受力变形分析。结果表明,超前导洞法对围岩应力和变形速率有一定控制作用;三层支护仍不足以长期控制变形发展,“三层初支+径向注浆+长锚杆+长锚索”支护系统施作完成后,满足设计施作第四层钢筋混凝土衬砌条件;木寨岭岭脊段在相同施工及支护参数条件下,施工的先后对变形的影响很小,地质条件是影响变形的主因;长锚杆形成系统承载后,整体受力明显减小,而锚索张拉后,短期锚固效果不明显。

The pilot heading is a method to release the stress by opening small guide hole at the section before tunneling.This paper studies the stress and deformation of each layer of support in the tunnel during the process of expanding the circular hole.Taking the ridge section of Muzhailing Tunnel as the research object,the data are obtained from the actual measuring points.The stress release effect analysis of pilot heading,deformation analysis of each layer in circular expansion,interaction analysis of expansion in successive tunneling,and stress deformation analysis of long anchor bolt and anchor cable are carried out.The results show that the pilot heading method has a certain control effect on the stress and deformation rate of surrounding rock.The three-layer support is still not enough to control the deformation development in a long term.After the completion of the support system of“three-layer initial support+radial grouting+long anchor bolt+long anchor cable”,the conditions for the construction of the fourth layer reinforced concrete lining can be satisfied.Under the same construction and supporting parameters,the construction sequence has little influence on the deformation,and the determining factor of the deformation is the geological condition.After the system bearing capacity of long bolt is formed,the overall stress is significantly reduced,while the short-term anchorage effect is not obvious after the cable is tensioned.