Excavation-Damaged Zone around Tunnel Surface under Different Release Ratios of Displacement

AbstractA tunnel excavation-damaged zone (EDZ) will gradually form with increasing release ratios of displacement (RRD) in the rock mass surrounding a tunnel. This paper presents a study of the longest subway tunnel in China, constructed with tunnel-boring machines (TBM) and the new Austrian tunneling method (NATM) in soft and weak rock ground. On the basis of the damage constitutive model, some studies are conducted using the FEM. The spatial distribution rules of EDZ and RRD are studied with a three-dimensional (3D) numerical simulation. The results show that the spatial support effect of the tunnel face is concentered in the range of approximately two times that of the tunnel diameter. A two-dimensional numerical simulation is carried out to study the relationship between the EDZ and RRD. The results show that the EDZ initiates when the RRD is more than 0.5, and the EDZ suddenly increases when RRD is more than 0.9.