Model test on the behavior of tunnel linings under earth pressure conditions and external water pressure

154-km long tunnels of major highways in Shanxi Province of China are observed, and 5120 crack distributions are obtained that are largely dependent on both earth pressure conditions and external water pressure. By conducting 1:30 scaled model tests, the cracking patterns of the mold lining induced by earth pressure are notably different from those induced by external water pressure. Under high external water pressure, moment-induced tensile failure occurs at the knee of the tunnel lining, and then flexural failure appears at the invert. Increasing the earth pressure can rapidly decrease the bending moment, moderately increase the axial thrust, and considerably enhance the structural safety of the tunnel lining provided that the earth pressure is less than 0.3 MPa. The ultimate water pressure, influenced by earth pressure, increases by approximately 17%, regardless of the ratio of horizontal to vertical stresses K. For a tunnel under high earth pressure, the upper parts of the tunnel lining are the locations most susceptible to failure, whereas the invert is safe with a large safety margin. Imposing external water pressure could substantially increase both the axial thrust along with the bending moment and suddenly worsen the structural soundness of the tunnel lining. Furthermore, the failure positions and cracking sequences are highly correlated with the values of K. These findings are supported by three-dimensional nonlinear finite element numerical modeling. Finally, the interaction of water pressure and earth pressure conditions is investigated under various ratios of horizontal to vertical stresses K in the ultimate limit state.

Automated summary

The study in Shanxi Province of China observed the crack distribution in tunnels of major highways, finding that earth pressure conditions and external water pressure have significant impacts on the tunnel lining's failure patterns. Increasing earth pressure can enhance structural safety, while external water pressure can exacerbate damage. The values of K are closely related to the positions of failure and crack sequences.