Seismic response and damage analysis of shield tunnel with bottom Karst caves under oblique SV waves

This paper investigates the dynamic responses of bottom karst caves on the shield tunnels under oblique SV waves according to the project of Dalian Metro Line 5. The viscous-spring artificial boundaries are employed and validated to assure the accuracy of seismic input. The characteristics of deformation and stress, damage evolution process and damage state of the tunnel are discussed, such as under different filling conditions of karst caves, incident angles of SV waves, the elastic modulus of grouting materials, and the combination of multiple karst caves. According to the relationship between tensile damage value and crack width, the damage state classification is divided. The results show that the tunnel's displacement and stress increase and the damage state is from no damage to severe damage with the increasing incident angle. When the incident angle is 30 degrees, the tunnel's displacement and stress reach to the maximum, and the axial cracks width higher than 0.2 mm appear on the outer surface of the vault and bottom. The filling conditions of the bottom karst caves can influence the tunnel's circumferential damage. The structural dynamic response does not change significantly when the elastic modulus of the grouting material is greater than 10 GPa. Compared with one single cave, the damage severity of the inner surface under the multiple karst caves with a large clear distance is weakened and tends to be averaged.