Calculation Method of Loose Pressure in Surrounding Rock Mass

With the implementation of the regional coordinated development strategy, traffic flow has grown explosively. The construction of a larger tunnel section becomes an effective way to solve the highway network's insufficient transport capability problem. Currently, there is little research on the factors influencing and methods of calculating the loose pressure in the surrounding rock mass for highway tunnels with super-large cross-sections. Based on the Bifurcation Tunnel, which is one of the sign projects in the past five years, this paper discusses the influencing factors for the range of loose zone in deeply buried tunnels using a combination of a numerical analysis and an orthogonal test. The weight of influencing factors is calculated via an efficiency evaluation method. This paper establishes a limit analysis model of the loose pressure in the surrounding rock mass under a non-linear failure criterion based on the fitted boundary function and upper bound limit analysis method and deduces the correlations of the loose pressure. The distribution law of the loose pressure, obtained via the limit analysis method, is consistent with the pressure-monitoring results, verifying the correctness of the proposed calculation method. This study can provide a calculation basis for the design of a supporting structure and the selection of similar super-section tunnel projects.