超浅埋小净距隧道洞口段安全评估及钢栈桥工艺

Safety Assessment and Steel Trestle Technology of Portal Section of Tunnel with Super Shallow Depth and Small Clear Distance

针对隧道出口段存在超浅埋、小净距与下穿既有公路的特殊性,为了确保上覆既有公路正常通车下隧道出口段安全施工,研发了在既有公路路面上钢栈桥架越隧道拱顶的新工艺及钢栈桥设计参数,首次提出了路面钢栈桥与拱顶保护壳复合式立体式隧道洞口段掘进安全防护体系.采用MidasGTSNX软件,对钢栈桥设置的合理性和有效性进行了仿真模拟,结果显示,路面存在车辆荷载前提下,钢栈桥的设置能有效减小围岩塑性区的分布面积,显著降低拱顶沉降,保持围岩稳定.实践表明:在既有公路路面上设置钢栈桥,能保证既有公路正常通车条件下的超浅埋与小净距下穿隧道的安全掘进,本研究结果对类似隧道工程洞口段安全施工有重要的借鉴意义.

It is a challenge to excavate safely a small clear distance tunnel which is buried under an existing road at a super shallow depth when the traffic on the road is not interrupted during the excavation.In order to solve this problem,a steel trestle technology with parameters is first proposed as the key measure to reduce risk for portal section of tunnel.The rationality and effectiveness of the steel trestle have been simulated with Midas GTS NX software.The numerical simulation shows that the steel trestle can reduce the distribution area of the plastic zone and the displacement of the surrounding rock mass,and maintain the stability of the tunnel which is threatened by the traffic load.The steel trestle is a commendable measure for safe excavation of super shallow and small clear distance tunnel undergoing an existing road where the traffic is not interrupted.