Mechanical problems for the long-term stability of rocks surrounding deep level underground tunnels

Based on the research of Academician Tan Tjong-Kie on the long-term stability mechanics of underground tunnel and considering Academician Sadovsky's structural hierarchy theories on complex geological rock masses, the inherent statistical mechanical properties of inhomogeneous structure and closed stress in deep rock masses were investigated. Two mechanical problems were mainly studied, i.e. characteristics of inherent non-uniform deformation and closed stress of rock masses, and long-term stability of deep tunnels. The quantitative mathematical characterization of inherent non-uniform deformation and closed stress of rock masses were given using the method of statistical mechanics. Based on the law of mass conservation, a general calculation method of long-term stability and deformation of rock masses surrounding deep level tunnels was proposed. The Maxwell model was used to calculate the threshold of splitting. A post-peak failure model of rock was established to estimate the in-situ stress at which rock undergoes post-peak failure. With the help of the theory of the hirerachical structure of rock masses, the maximum value of rock displacement due to splitting dilatation was obtained. A dimensionless energy factor was introduced to define the extent of zonal disintegration of surrounding rock masses. It was concluded that the splitting and dilatancy deformation is the main part of the deformation of surrounding rocks. The reasons why unloading splitting failure is more likely to take place in rock masses surrounding deep level tunnels were explained. The split evolution pattern of rock masses surrounding deep level tunnels and the calculation method of dilatancy displacement were obtained. The calculation results of the range of loosening zone, the location of the rupture zone in rock masses surrounding deep level tunnels, and the displacement of the sidewall were compared with the existing monitoring data in the underground powerhouse of the Jinping Ⅰ Hydropower Station, and the agreement is good. © 2021, Editorial Staff of EXPLOSION AND SHOCK WAVES. All right reserved.