下穿既有高速公路的隧道超前支护措施与开挖方法研究

Research on Advance Support Measures and Excavation Methods for Tunnels Underneath an Existing Expressway

某新建隧道下穿既有高速公路,该区域土体较差,隧道围岩等级为V级。本研究基于有限元软件FLAC3D,以降低对既有高速公路影响为原则,利用有限元仿真对比分析无超前支护措施、小导管注浆、小导管+单层管棚和小导管+双层管棚4种超前支护措施和三台阶七步法、CD法、双侧壁导坑法3种开挖方法。本研究选取的控制分析指标主要有高速公路地表沉降值、隧道洞周位移、初期支护拉压应力。仿真结果表明,超前支护为小导管注浆的双侧壁导坑法和超前支护为双层管棚的三台阶七步法均满足要求,综合对比分析施工应力应变、工期和成本等因素,并考虑到该隧道工程地质条件较差,参照同地区类似项目的做法,推荐的综合施工方法为超前支护为双层管棚的三台阶七步法。

A new tunnel underpasses an existing expressway,the soil in this area is poor,and the surrounding rock of the tunnel is grade V.In this paper,based on the finite element software FLAC3D,based on the principle of reducing the impact on the existing expressway,the finite element simulation calculation is used to compare and analyze 4 types of advanced support measures for pipe sheds,including the non-advanced support measures,small pipe grouting,small pipe+single layer pipe shed and small pipe+double layer,and 3 excavation methods,including three steps and seven steps,CD method,and double-side pilot pit method.The control analysis indexes selected in this paper are mainly the surface settlement value of the expressway,the displacement of the tunnel circumference,and the tension and compression stress of the initial support.According to the simulation results,the doublesided pilot pit method with small pipe grouting for the advance support and the three-step seven-step method with the double-layer pipe roof for the advance support meet the requirements.The construction stress and strain,construction period and cost are comprehensively compared and analyzed.Considering the poor geological conditions of the tunnel,and referring to the practice of similar projects in the same area,the recommended comprehensive construction method is the threestep seven-step method with advanced support as a double-layer pipe shed.