Abstract
Considering engineering problems such as complicated stress and the difficulty in controlling large deformation while a tunnel passes through a soft rock stratum, a theoretical prediction model of convergence deformation of tunnel-surrounding rock is proposed. Based on the longitudinal displacement profile curve reflecting the “space effect” of the excavation surface, the Hoek formula with better applicability was introduced to analyze and theoretically deduct the “time–space effect comprehensively.” By taking the influence of the “time effect” coefficient into account, an improved Nishihara model was established to derive the analytical equation of the viscoelastic–viscoplastic convergence of surrounding rock. Taking the Dingxi Tunnel of Wujing Expressway in Hunan Province, the physical and mechanical parameters of surrounding rock in the tunnel were firstly determined then they were used to calculate and predict the vault down of three typical sections with the scoping equation of surrounding rock deformation. Based on the calculation results, the causes of the differences between the measured and theoretical values were analyzed; moreover, it is indicated that the minimum root-mean-square error is 1.68, the minimum average error is 1.3%, and the correlation coefficient is 0.99. The comparison shows that the theoretical prediction results agree well with the corresponding field test results. The improved Nishihara model can accurately predict the final deformation of the surrounding rock. Simultaneously, it is also proved that the relevant parameters and the hypothesis and correlation of the nonlinear viscosity coefficient equation are reasonable, with particular effectiveness and applicability in practical engineering. This study is significant for further studying the tunnel-surrounding rock’s stability and accumulating theoretical and practical experience to develop rheological theory.
Highlights
In China, the center of tunnel construction is gradually shifting to the southwest and northwest
The Nishihara model can describe the deformation of rock masses in tunnel engineering, such as sandstone, limestone, sandy shale, clay shale, and carbonaceous shale
This study derived the analytical equation of the viscoelastic–viscoplastic convergence of surrounding rock based on the improved Nishihara model with the Matlab software
Summary
In China, the center of tunnel construction is gradually shifting to the southwest and northwest. Considering the influence of time and stress on creep, some scholars established a nonlinear creep damage model and the corresponding constitutive equation (Feng et al, 2020; Liu W. et al, 2020; Yan et al, 2020; Liu Y. et al, 2020) They did not study the influence of this model on the damage and deformation of surrounding rocks. Previous scientific research achievements have made significant contributions to the optimization and improvement of the Nishihara model and the development of the prediction theory of tunnel-surrounding rock deformation, but there are still some shortcomings. Considering the time-space effect of the plastic viscosity coefficient, an improved Nishihara model is established to study the deformation process of surrounding rock in the process of tunnel excavation and support. A comparative study is carried out combined with engineering cases to provide theoretical support and technical reference for the design and construction of tunnel engineering
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