大断面古土壤隧道围岩压力分布规律及支护结构受力特征分析——以银西高铁早胜3号隧道为例

Surrounding Rock Pressure Distribution Law and Supporting Structure Stress Characteristics of Large Cross-section Paleosol Tunnel: a Case Study of Zaosheng No.3 Tunnel on Yinchuan-Xi′an High-speed Railway

银西高铁早胜3号隧道位于甘肃省宁县境内,为国内首条穿越古土壤地层的隧道。为研究隧道穿越古土壤地层时围岩压力分布情况及支护结构受力变形特征,通过在隧道相同里程布设压力盒、表面应变计和钢筋应力计等传感器,对围岩压力、初期支护受力变形情况进行长期现场监测,并将监测结果得到的频率值换算为力值或应变,最后对数据进行分析。结果表明:1)对于三台阶七步开挖法,围岩压力大致经历了急剧变化—缓慢变化—平稳变化3个阶段,三台阶七步开挖的施工工法决定了相同里程先开挖一侧围岩压力明显大于后开挖一侧; 2)钢拱架呈现三维受力状态,相邻2榀拱架间轴力以受压为主,支护结构的完整程度以及与混凝土的协作关系直接影响轴力变化情况; 3)拱脚应变的最大值主要集中在上台阶和仰拱底部附近。

Zaosheng No.3 Tunnel on Yinchuan-Xi′an High-speed Railway, the first tunnel crossing paleosol stratum in China, is located in Ningxian County, Gansu Province. In order to study the pressure distribution of surrounding rock and the stress and deformation characteristics of supporting structure when tunnel crossing paleosol stratum, the pressure box, surface strain gauge and steel bar stress gauge are installed at a same mileage of tunnel to monitor the pressure of surrounding rock and the stress and deformation of primary support for a long time. And then the frequency obtained is converted to force or strain, and finally the data are analyzed. The results show that:(1) For the three-bench seven-step excavation method, the pressure of the surrounding rock has experienced three stages, i.e. rapid change, slow change and steady change;by using the three-bench seven-step excavation method, the pressure of the surrounding rock excavated firstly is obviously larger than that at the side excavated lately at a same mileage.(2) The steel arch presents a three-dimensional stress state, the axis force of the two adjacent arches is mainly subjected to pressure, and the degree of integration of the supporting structure and the cooperation with the concrete directly affect the axial force.(3) The maximum strain of the arch feet is mainly concentrated on the bottom of the top heading and the bottom of the inverted arch.