Tunnel lining segment deformation and cracking mechanisms during tunneling in complex mixed grounds with the combined mining and shield tunneling method

The combined mining and shield tunneling method solves the challenge that shield machine is slow to excavate hard rock formations during tunneling in complex mixed grounds such as soft soils mixed with hard rocks, which, however, causes the deformation and cracking of tunnel segments. Both in-situ field measurements and three-dimensional numerical simulations are conducted in this study to analyze the segment deformation and cracking mechanism of a tunnel excavated in complex mix grounds with the combined mining and shield tunneling method. It is concluded that the segment deformation and cracking are caused by insufficient pea-gravel fillings and uneven grouting pressures. To ensure the tunnel ovality satisfying standards and minimize the segment deformation and cracking, the angle range of the tunnel wrapped in the pea gravel should be greater than 180° and the resistance coefficient provided by the filling layer after grouting should be greater than 20 MPa/m. Moreover, it is found that the difference between the grouting pressures at the top and bottom of the tunnel has a significant impact on the overall deformation and opening amount of the joints between the segments.