浅埋偏压隧道洞口钻爆设计及支护体系研究

Study on drilling and blasting design and support system of shallow bias tunnel portal

洞口是浅埋偏压隧道工程的关键性控制节点,钻爆施工不当极易造成地表沉降过大、洞口塌方、边坡滑移等安全事故,提出一套系统完整的软弱围岩浅埋偏压隧道洞口钻爆设计方案及支护体系迫在眉睫。依托成都市东西城市轴线(东段)工程龙泉山二号隧道为工程背景,通过对开挖工法、钻爆参数、支护体系等的研究,形成了一套系统完整的软弱围岩浅埋偏压隧道洞口段钻爆施工方案。研究结果表明,超前管棚对掌子面前方围岩进行加固,形成类似拱壳的连续体,可主动承担上方围岩压力,同时管棚提供的抗剪力提高了整体的抗剪、抗弯能力,稳定了有滑移风险的岩体;管棚直径越大,地表沉降越小,控制效果越好,更有利于促进隧道掌子面稳定;采用“规范钻爆作业、优化钻爆参数设计以及大管棚超前支护”的施工方案可有效控制地表沉降,降低隧道拱顶塌方风险,确保施工安全和施工正常进行。

The entrance of the tunnel is the key control node of the shallow-buried bias tunnel project.Improper drilling and blasting construction can easily cause safety accidents such as excessive surface settlement,collapse of the entrance,and slope slip.Therefore,it is urgent to propose a systematic and complete drilling and blasting design scheme and support system for the entrance of shallow-buried bias tunnel in weak surrounding rock.Based on the engineering background of Longquanshan No.2 Tunnel of Chengdu East-West City Axis(East Section)Project,this paper studies the excavation method,drilling and blasting parameters and supporting system,and forms a set of systematic and complete drilling and blasting construction scheme for the portal section of shallow buried bias tunnel in weak surrounding rock.The results show that the advanced pipe shed reinforces the surrounding rock in front of the tunnel face,forms a continuum similar to the arch shell,and takes the initiative to bear the pressure of the surrounding rock above;at the same time,the shear resistance and tensile resistance provided by the pipe roof improve the overall shear and bending resistance,and stabilize the rock mass with slip risk.The larger the diameter of the pipe shed,the smaller the surface settlement,the better the control effect,and the more conducive to promoting the stability of the tunnel face.The construction scheme of standardizing drilling and blasting operation,optimizing drilling and blasting parameter design and large pipe roof advance support can effectively control the surface settlement,reduce the risk of tunnel vault collapse,and ensure the construction safety and normal construction.