软弱围岩浅埋连拱隧道力学特征测试与分析

In-situ Test and Analysis of Mechanics Properties of Shallow Buried Multi-arch Tunnel in Soft and Weak Rock

为研究软弱破碎围岩浅埋连拱隧道支护体系力学特性,以某连拱隧道为依托,采用钢弦式传感器,对围岩压力、锚杆轴力、钢支撑内力、二衬受力及中墙内力等进行系统测试与分析。结果表明,拱部两侧拱腰位置围岩压力较大,呈"猫耳朵"分布。受地质和施工因素等的影响,拱部围岩压力实测值与公路隧道设计细则计算值相差较大。中墙底部及两侧边墙底部基底压力大。正洞锚杆轴力量值很小,建议取消正洞锚杆。侧导洞锚杆作用明显,根据围岩情况可以保留。钢拱架受力最大位置在拱腰处,拱顶处钢拱架承受拉应力,其他部位为压应力,部分拱架受力接近屈服,型钢拱架作用十分明显。中墙顶部钢筋计受拉,其余位置受压,中墙上部受力较下部敏感。左右线先后应力释放对中墙有一定的"纠偏效应",但中墙受力始终处于偏压状态。

In order to understand the mechanic properties of shallow multi-arch tunnel in soft and weak rock, large scale in-situ tests are conducted based on a multi-arch tunnel project. The contacting pressure on the surrounding rock and middle-wall, axial force of anchors, stress of steel arch Centering and the internal force of middle-wall are systematically monitored by the steel string transducer. The test results indicate that： （1） The surrounding rock pressure approximately take on as ＂cat ears＂ distribution, Which is larger on the tunnel hance. Under the influence of factors such as geology and construction, the surrounding rock pressure in tunnel arch has larger difference between measured value and calculated value. The pressure is large at the bottom of middle-wall and side walls. （2） The axial force of anchors in main tunnel is little, which is suggested to be cancelled in main tunnel. The axial force of anchors in pilot tunnel is large, and the anchors of pilot tunnel should be retained according to the conditions of surrounding rock. The stress of steel arch centering in tunnel hance is the largest. The＇stress of steel arch centering in the tunnel vault is tensile stress, which is pressure stress in other places. The stress of Some steel arch centering is close to the yield limit. The steel arch centering supporting effect is very obvious. （3） The axial forces of rebar at the bottom of middle-wall is tensile stress, which is pressure stress in other places. The pressure at the top of middle-wall is more sensitive than the bottom. The stress in the middle- wall lower left-central side is the largest, and the stress release of right and left holes has a certain ＂corrective＂ action on the stress of middle-wall, but the m!ddle-wall has always been affected by biaspressure.