极小覆岩厚度条件下地铁隧道逆台阶法开挖稳定性分析

Stability Analysis of Surrounding Rock of Inverse Bench Excavation of Metro Tunnel with Minimal Overburden Thickness

为减少台阶法施工时爆破扰动对隧道上覆围岩稳定性的影响,针对极小覆岩厚度条件下的隧道塌方问题,提出适用于极小覆岩厚度条件下的逆台阶开挖工法(下台阶先行开挖,再通过爆破控制技术开挖上台阶),并依托青岛地铁某区间隧道,通过有限元软件FLAC 3D对逆台阶法开挖稳定性进行数值模拟分析。模拟结果与工程实践表明,在极小覆岩厚度条件下,采用逆台阶法先行开挖下台阶可额外为上台阶提供开挖临空面,从而有效减少上台阶爆破扰动对上覆围岩力学性能和完整度的影响,充分保护上覆围岩的承载能力,保障地铁隧道开挖安全。

Blasting disturbance for tunnels excavated using bench method greatly influences the stability of the overlying surrounding rocks.This may result in tunnel collapse in the case of minimal overburden thickness.Thus,to address the above problem,an inverse bench excavation method,i.e.,the lower bench goes first and then the top heading is excavated by blasting control technique,is proposed.The stability of surrounding rocks excavated by inverse bench method is numerically simulated using a case study of a metro tunnel excavation in Qingdao by applying the FLAC 3Dfinite element analysis software.The simulation results and engineering practice show that,under minimal overburden thickness,the inverse bench excavation can provide extra excavation free face for the top heading.This effectively reduces the blasting disturbance to the mechanical properties and integrity of the surrounding rocks,protecting their bearing capacity and guaranteeing the excavation safety of the metro tunnel.