Nonlinear energy consumption analysis of shallow-buried bias tunnel stability with improvement of failure mode.

Numerous tunnels are often sited in shallow depths and sloping strata due to topographic and geomorphological constraints, however, the evolutionary mechanisms of slip surfaces and instability patterns under asymmetric loading remain unclear. On the basis of the Terzaghi failure hypothesis and the logarithmic spiral failure mode of shallow tunnels in slope areas, combined with the nonlinear failure criterion of soil and the upper bound theorem of limit analysis, this study proposes a new calculation formula for the surrounding rock pressure of shallow tunnels in slope areas considering slope top loads. By using the SQP algorithm in MATLAB software to optimize the solution, this study elucidated and analyzed the effects of the slope top load, buried depth ratio, initial cohesion and axial tensile stress on the surrounding rock pressure and failure mode of shallow buried tunnel. This analysis revealed that when the nonlinear coefficient of rock and soil increases and the ratio of the horizontal support reaction force to the vertical support reaction force decreases, the surrounding rock pressure under the logarithmic spiral failure mode of shallow buried tunnel increases. The increase of initial cohesion will lead to the reduction of surrounding rock pressure. The stability of the surrounding rock pressure of shallow buried tunnel decreases with increasing slope top load, buried depth ratio and axial tensile stress. With the increase of the load on the top of the slope and the buried depth ratio, the failure of the shallow tunnel deflects toward the shallow side of the slope. The research findings provide crucial guidance for ensuring safe construction practices in shallow-buried tunnels.