An improved classification method of asymmetrical squeezing large deformation of layered soft rock tunnels under high geo-stresses

In order to explore the classification method of asymmetrical large deformation of high stress layered soft rock tunnels, deformationdata of 200 tunnels in soft rock are collected, and the major factors of asymmetrical deformationare analyzed. Relative deformation and asymmetrical deformation positions of the tunnels under high geo-stresses are investigated based on the association rule, and an improved classification method of asymmetrical squeezing deformation is put forward. The results show that the asymmetry factors are the inclination angle of the strata(α), the angle between the rock strike and the tunnel axis(β), and the angle between the maximum principal stress of the initial stress field and the rock plane(γ). 20 strong association rules, about the basic factor(compression stress and maximum principal stress) along with the relative deformation, and asymmetrical factor(α, β, γ)corresponding to asymmetrical deformation position, are obtained. It is revealed that α, β and γ together control the asymmetrical deformation position, which shifts from the sidewall and the bottom to the vault with increasing α, from the arch and the sidewall to the bottom with increasing β, and from the bottom to the sidewall and then to the vault with increasing γ. The strength-stress ratio and the relative deformation determine the basic level of the squeezing, and the asymmetry factorsα, β, γ as sub-indexes identify the squeezing deformation position. The proposed method according to the level of the squeezing and the asymmetry factors provides an important approach for the asymmetrical large deformation classification of layered soft rock tunnels. © 2022, Science Press. All right reserved.