大断面浅埋黄土隧道围岩变形特性分析

Analysis on Deformation Characteristics of Surrounding Rock in Large Section Shallow Loess Tunnels

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 the Xinzhou loess tunnel as the engineering back-ground,by using site monitoring to measure deformation characteristics of surrounding rock in three-bench seven-step excavation method.The full excavation sequence has been simulated using Midas/GTS finite element software.It is verified by elastic-plastic analysis on vault crown settlement.The results show that ground settlements,crown settlements and convergence change obviously during excavation of benches,especially for upper bench.The ground settlements,crown settlements and convergence around the tunnel take up 85% 、80% and 90% of the total deformation.It is necessary to seal the invert in order to control the oversize deformation of the surrounding rock.Surrounding rock displacement 4.5 meters away from span tunnel takes up24% ~ 50% of that 1.5 meters away.It is larger in vault and springing arch.There is a good relationship between the distribution of plasticized zone of surrounding rock through numerical analysis and that measured.Arch springing is the most dangerous in construction and it must be enforced.Numerical analysis and analytical solutions show good agreement with the field test data,but they are larger by 16% and 11% than the measured values.