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以忻州大断面黄土隧道为工程背景,针对三台阶七步开挖法施工条件下的围岩变形特性进行了现场测试分析,采用Midas/GTS三维有限元软件进行施工模拟分析,并结合隧道围岩位移弹塑性解析法进行了验证。分析结果表明:地表沉降、拱顶下沉及洞周水平收敛随上、中、下台阶的开挖变化较大,尤其是下台阶的开挖,其收敛出现突变;仰拱浇筑前,拱顶和地表沉降及洞周水平收敛占总变形比例分别为85%、80%和90%,且仰拱施作完成后变形基本稳定;各部位围岩内部位移与距开挖轮廓线距离成反比,距开挖轮廓线4.5 m处约为1.5 m处的24~50%,且拱顶和拱脚处围岩内部位移较明显,数值计算塑性破坏区分布与实测结果吻合;支护时机与强度对围岩后期变形仍存在一定的影响,拱脚是施工中的薄弱部位,应提高支护强度;拱顶下沉数值计算和弹塑性解析解与实测结果变形规律基本吻合,且较实测值分别大16%和11%。
Taking Xinzhou large-section loess tunnel as the engineering background, the deformation and deformation of surrounding rock under the three-step seven-step excavation method were tested in the field. The construction simulation was carried out by using the 3D finite element software Midas / GTS. Combined with the tunnel surrounding rock Displacement elastoplastic analytical method was verified. The analysis results show that the settlement of the earth’s surface, the vault settlement and the horizontal convergence of the cave circumference vary greatly with the excavation of the upper, middle and lower steps, especially the excavation of the next step, whose convergence has a sudden change. And the settlement of the earth’s surface and horizontal convergence of the hole circumference account for 85%, 80% and 90% of the total deformation, respectively, and the deformation of the inverted arch is basically stable. The displacement of the surrounding rock of each part is inversely proportional to the distance from the excavation contour line, Which is 24-50% away from the excavated contour 4.5 m at 1.5 m, and the displacement of the surrounding rock in the vault and arch foot is obvious. The distribution of the numerical value of the plastic failure zone agrees well with the measured results. The timing and strength of support The late deformation of surrounding rock still has some influence. The arch foot is a weak part in the construction, and the support strength should be increased. The numerical calculation and elastic-plastic analytical solution of vault settlement basically agree with the measured results, 16% and 11%.