Three-Dimensional Fluid–Solid Coupling Numerical Simulation of Effects of Underlying Karst Cave on Shield Tunnel Through Sand Stratum

This paper is based on the construction project of Wuhan Metro line 6 from Qianjincun Station to Mayinglu Station. In view of the geological condition of overlying sand and underlying limestone, by using FLAC3D5.0 software and considering the fluid–solid coupling effect, the influences of distance between karst cave roof and bedrock surface d, cave diameter D, width w and filling degree ω on the deformation and force of subway tunnel segment after excavation are analyzed. The results show that: (1) The vertical settlements and the axial forces at vault and arch bottom are negatively correlated with d and ω. The axial force at right hance and bending moments at each control point are positively correlated with d and ω. (2) With the increase of D and w, the vertical displacements and axial forces at vault and arch bottom tend to increase. The axial force at right hance and bending moments at each control point have a negative correlation with D and w. (3) Compared with other control points, the axial force and bending moment of arch bottom are the largest and the bending moment of right hance is the smallest. (4) The greater d, the smaller the amplitude of variation of the displacements and internal forces of the segment. The greater D, w and ω, the greater the amplitude of variation of the displacements and internal forces of the segment. The research results can provide guidance for similar engineering.