Study And Application Of Stress Release Ratio In Weak Rock Tunneling

During the excavation of tunnel, the stress field adjustment mechanism of the surrounding rock is relatively complicated, and thus, the tunnel supporting design and tunneling scheme selection are closely related to the stress release ratio. Hence, it is necessary to make the stress release ratio of each stage clear during the tunneling, which can not only control the excavation risk effectively, but also can reduce the excavation cost. However, the investigations on the method to determine the tunneling stress release ratio are scarcely, and more importantly, how to simply and effectively determine the stress release ratio in tunnel excavation is one of the most urgent problems in tunneling. In this study, a series of research work is conducted, focusing on the solution and application of tunneling stress release ratio.Firstly, the process of tunnel excavation was simulated on the basis of the Mohr-Coulomb model and Burger-creep Viscoplastic model, respectively, and comparison is conducted between the numerical results and the measured data to investigate the necessity of considering time effect in the tunneling process. Then, an improved method was proposed to solve the stress release ratio via the solution of volume loss ratio. This proposed method is based on the principle that the stress release ratio can be approximately equivalent to the release ratio of displacement, which adequately considers the time-space effect during tunnel excavation.Secondly, a series of cases, including different tunneling schemes, tunnel depths and deformation modulus of surrounding rock was studied to obtain the corresponding stress release ratio using the method proposed in this investigation. All the obtained stress release ratios can be used as the reference for similar tunnels and offer a basis to transform three-dimensional model into two-dimensional model in tunneling simulation with the reverse stress method. Meanwhile, the numerical results can provide theoretical guidance for the similar tunnel supporting design and the optimization of the excavation method.Finally, on the basis of the obtained stress release ratio, a series of two-dimensional model has been carried out using the reverse stress method. Comparison analysis is then conducted between the results of the two-dimensional model and those of the typical sections of three-dimensional model to verify the reliability and practicability of the stress release ratio obtained by the improved method proposed in this study. Moreover, parametric study is performed to identify the effects of two key factors, i.e., the tunnel depth and surrounding rock deformation modulus, on the dimension reduction.