Abstract: 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 3D finite 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.

Key words: tunnel engineering, blasting disturbance, minimal overburden thickness, reverse bench method, numerical simulation, excavation stability