粉煤灰地层大断面连拱隧道开挖进尺研究

Study on Excavation Footage of Large Section Multi Arch Tunnel in fly ash Stratum

粉煤灰地层具有结构松散、强度低、孔隙率大、物理不均匀等特点,隧道穿粉煤灰地层工程地质差因此施工难度大。本文依托盐坪坝隧道研究了开挖进尺对围岩稳定性的影响,利用Rhinoceros建立盐坪坝隧道大断面连拱隧道的网格模型并导入FLAC3D软件中进行数值计算,研究表明:当进行上台阶环形开挖时围岩变形出现突变,开挖进尺对隧道拱顶、拱肩位移影响较大,开挖进尺从2.0 m增加到3.0 m时拱顶变形增加1.09 mm,拱肩变形增加0.9 mm,远大于开挖进尺从1.0 m增加到2.0 m时的变形,考虑开挖安全和施工进度,最终选用2.0 m为施工循环进尺。

Fly ash stratum has the characteristics of loose structure,low strength,large porosity and uneven physical.The engineering geology of tunnel passing through fly ash stratum is poor,so it is difficult for us to construct.Based on yanpingba tunnel,this paper studies the influence of excavation footage on the stability of surrounding rock,establishes the mesh model of yanpingba tunnel large cross-section multi arch tunnel by rhinoceros,and imports it into FLAC3D software for numerical calculation.The results show that:when the circular excavation of upper steps is carried out,the deformation of surrounding rock changes suddenly,and the excavation footage has a great influence on the displacement of tunnel vault and abutment,When the excavation footage increases from 2.0 m to 3.0 m,the vault deformation increases by 1.09 mm,and the arch shoulder deformation increases by 0.9 mm,which is much larger than the deformation when the excavation footage increases from 1.0m to 2.0 m.Considering the excavation safety and construction progress,2.0 m is selected as the construction cycle footage.