Abstract
A large number of experimental studies show that the mechanical parameters of deep buried surrounding rock show significant attenuation characteristics with the increase of strain from the rheological acceleration stage to the attenuation stage. However, the existing numerical models all take mechanical parameters as constants when describing the rheological behavior of surrounding rocks, which can only be applied to the stability analysis of the shallowly buried tunnel. Therefore, this work proceeding from the actual project, improved the sandstone rheological constitutive model and optimized the algorithm of parameter inversion, and put forward a long-term stability analysis model that can accurately reflect the rheological characteristics of surrounding rocks under the complex geological condition including high stress induced by great depth and high seepage pressure. In the process, a three-dimensional nonlinear rheological damage model was established based on Burgers rheological model by introducing damage factors into the derivation of the sandstone rheological constitutive model to accurately describe the rheological behaviors of the deep buried tunnel. And BP (Back Propagation) neural network optimized by the multi-descendant genetic algorithm is used to invert the mechanical parameters in the model, which improves the efficiency and precision of parameter inversion. Finally, the rheological equation was written by using parametric programming language and incorporated into the general finite element software ANSYS to simulate the rheological behavior of the tunnel rock mass at runtime. The results of the model analysis are in good agreement with the monitoring data in the later stage. The research results can provide a reference for the stability analysis of similar projects.
Highlights
At present, the cross-basin water diversion project, cross-river and cross-sea passageway, and large-scale hydropower project under construction and planning in China often involve the problem of deep-buried tunnels, which has become the main project, or control project of the whole project construction
The Wawushan Hydropower Station requires the construction of a high dam and deep excavation of a diversion tunnel, with the maximum buried depth of about 510m, and abundant underground water
Taking the complex environment of high in-situ stress and the characteristics of the sandstone rock mass of the deep buried diversion tunnel of Wawushan Hydropower Station as the research background, damage factors were introduced into the deduction of the sandstone rheological constitutive model based on Burgers rheological mode, and a three-dimensional nonlinear rheological damage model was established to describe the rheological characteristics of sandstone accurately
Summary
The cross-basin water diversion project, cross-river and cross-sea passageway, and large-scale hydropower project under construction and planning in China often involve the problem of deep-buried tunnels, which has become the main project, or control project of the whole project construction. The Wawushan Hydropower Station requires the construction of a high dam and deep excavation of a diversion tunnel, with the maximum buried depth of about 510m, and abundant underground water In such a high stress and high external water pressure environment, the rheological characteristics of the surrounding rock will become very significant and complex, especially the mechanical parameters of the surrounding rock which shows remarkable attenuation with the increase of creep strain. Taking the complex environment of high in-situ stress and the characteristics of the sandstone rock mass of the deep buried diversion tunnel of Wawushan Hydropower Station as the research background, damage factors were introduced into the deduction of the sandstone rheological constitutive model based on Burgers rheological mode, and a three-dimensional nonlinear rheological damage model was established to describe the rheological characteristics of sandstone accurately. The rheological equation was written by using parametric programming language and incorporated into the general finite element software ANSYS [16,17,18,19,20] to simulate the rheological, mechanical behavior of the tunnel rock mass under the condition of water filling, and the surrounding rock displacement, stress, plastic zone and support stress of the tunnel were obtained, so as to comprehensively evaluate the long-term stability of the project
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