Discrete element-based regression analysis of initial ground stress and application to an extra-long tunnel in China

The understanding of the initial ground stress field in deeply buried tunnels can help optimize the design of the support structure and reduce the occurrence of accidents such as collapse during the construction and operation of the tunnel. Yiliang tunnel is an extra-long deep buried tunnel with complex stratigraphic lithology. In this paper, the regression analysis of the initial ground stress field of Yiliang tunnel is studied with the help of discrete elements and compared with finite elements. Firstly, the finite element and discrete element calculation methods are used to establish separate computational models, and the stress field distribution in the tunnel axis is obtained by the multiple linear regression method combined with the least squares optimization criterion. The results show that the distribution of the stress field in the Yiliang tunnel area is dominated by the tectonic stress. The horizontal stress is greater than the vertical stress in the complex geological structure; in the smooth stratum, the horizontal stress is smaller than the vertical stress; the extreme value appears at the maximum burial depth. Due to the lithological transformation of the stratum, there is stress relaxation at the transformation. The results obtained from the combination of two numerical calculation methods and regression analysis, respectively, are basically consistent with the measured values, and the relative error is controlled within 25%. Overall, the discrete element is more stable in result error, and the simulation results are closer to the measured results than the finite element, which has higher applicability.