Effects of the friction coefficient and location of the dislocation surface of an active fault on the mechanical response of a freeway tunnel

Tunnels crossing active faults can be severely damaged by fault dislocation. Based on a freeway tunnel crossing an active fault, a three-dimensional numerical model is established to investigate the influences of the friction coefficient and position of the dislocation surface on the tunnel response under the action of right-lateral strike-slip reverse fault dislocation. The results show that the friction coefficient of the dislocation surface has little effect on the deformation characteristics in the tunnel but has a slight effect on the stress distribution. As the friction coefficient increases from 0.3 to 1.0, the stress distribution shape in the tunnel basically remains unchanged, while the maximum absolute values of the principal stresses decrease. The dislocation position has a significant effect on the deformation and stress distribution in the tunnel. When the fault moves along the interface between the fracture zone and the intact rock mass in the hanging wall or footwall, the deformation of the tunnel is the most severe, and the local stress concentration is also the most severe. In view of the local damage, amongst the conditions studied here, the condition of fault dislocation occurring along the interface between the fracture zone and the intact rock mass is the most dangerous and the condition of dislocation occurring along the fracture zone is safest. Under fault dislocation, the tunnel deformation is the most obvious in the fracture zone and tends to decrease to both sides; the principal stress in the tunnel peaks in the fracture zone and decreases to the two sides. The tunnel may be seriously damaged in the fracture zone and fault walls within 5 m of both sides of the fracture zone, and the tunnel fortification length is 3.39 times the fault width of 90 m. Disaster mitigation measures should be adopted for the tunnel design within the fortification range.