Effect of activities of ground fissures on crossing metro tunnels

Based on the distribution and movement of ground fissures and the condition of No. 2 metro tunnel in Xi’an, a geological model is established. Through the numerical analysis of finite element model, the protection range of the metro tunnel crossing ground fissures and its most dangerous section are confirmed by analyzing its deformation and stress states, and then, the distribution characteristics of surrounding rock pressure are studied so as to provide a basis for simplification of the model to calculate the stress of the metro tunnel crossing ground fissure. The results show that the main protection range of deformation and stress of the metro tunnel is from the location at the upper wall 40 m to that at the lower wall 30 m away from the fissure, that the most dangerous section is mainly distributed at the place of the ground fissure with a distance of 15~20 m at both sides, and that the structure in the range of 15 m away from the fissure at both sides suffers the maximum shear stress. The vertical pressure above the metro tunnel at the upper wall near the fissure is greater than that at the bottom, and the latter may be ignored. Therefore, the section of the metro tunnel crossing the fissure should be regarded as a beam which is sustained at the two sides of the subsiding area, and the vertical pressure of wall rock used to confirm the flexural torque produced by the activity of ground fissures should be calculated by the theory of stress transfer.