Probability Analysis of Deep Tunnels Based on Monte Carlo Simulation: Case Study of Diversion Tunnels at Jinping II Hydropower Station, Southwest China

During the construction of deep-buried diversion tunnels, many uncertainties exist in the variables governing the safety of the support structure, which will affect the safety of the tunnel. Therefore, the probability analysis of the deep tunnel based on Monte Carlo simulation is analyzed. For that a case study of diversion tunnels at Jinping II hydropower station, southwestern China is selected and analyzed. First, the dispersions of geostress and marble mechanical parameters are studied based on the field monitoring of the bolt stress and the laboratory testing of the Jinping marble. Subsequently, the statistical characteristics of the radial subgrade modulus are obtained considering the 100,000-fold sampling. Finally, the influence of the main uncertain factors on the internal force and deformation of the supporting structure is examined through the establishment of a numerical model. The maximum bending moment and axial force appear in the vault and invert of the tunnel, respectively. When the design requires the reliability of the tunnel support structure to achieve 90% in the case of Jinping II hydropower station, the value of the bending moment and the axial force cannot be higher than 0.57 MPa and 8.0 MN, respectively. The factors those having a greater impact on the safety of the tunnel support structure are the vertical load and the radial subgrade modulus.