粉煤灰地层大断面连拱隧道围岩变形规律研究

Study on the Law of Surrounding Rock Deformation of Large-section Double-arch Tunnel in the Layer of Pulverized Coal Ash

粉煤灰地层具有自稳能力差、结构松散、吸水性强、不均匀等特点,因此在该地层修建大断面隧道施工难度极大。本文以盐坪坝隧道为依托,利用Rhinoceros建模并将模型导入FLAC3D计算,对大断面连拱隧道穿粉煤灰地层掌子面附近围岩变形规律进行研究。研究结果表明:中导洞-左右侧壁预留核心土法和中导洞-左右侧壁台阶法开挖时,竖向位移普遍大于水平位移,水平最大位移出现在右洞拱脚约9 mm处,竖向最大位移出现在右洞拱肩约24 mm处,左洞先开挖产生的偏压作用导致右洞围岩位移明显增大,其中中导洞-左右侧壁台阶法在施作二次衬砌后围岩变形速率更大,因此选择中导洞-左右侧壁预留核心土法更有利于围岩稳定。

The layer of pulverized coal ash has the characteristics of poor self-stability,loose structure,strong water absorption,and unevenness.Therefore,it is extremely difficult to construct large-section tunnels in this stratum.Based on the Yanpingba Tunnel,this paper uses Rhinoceros modeling and imports the model into FLAC3D calculation to study the deformation law of surrounding rock near the face of a large-section double-arch tunnel passing through the layer of pulverized coal ash.The research results show that the vertical displacement is generally larger than the horizontal displacement when the middle pilot tunnel-left and right side wall reserved core soil method and the middle pilot tunnel-left and right side wall step method are excavated.The research results show that the vertical displacement is generally larger than the horizontal displacement when the middle pilot tunnel-reserved core soil method on left and right side walls and the middle pilot hole-left and right side wall step method are excavated.The maximum horizontal displacement appears at the arch of the right hole at about 9mm,and the maximum vertical displacement appears at the arch of the right hole at about 24mm.The bias caused by the first excavation of the left cave led to a significant increase in the displacement of the surrounding rock of the right cave.Among them,the middle pilot tunnel-left and right side wall step method has a larger deformation rate of surrounding rock after the secondary lining is applied.Therefore,the middle pilot tunnel-reserved core soil method on left and right side walls is more conducive to the stability of the surrounding rock.