| Large deformation of deep buried soft rock tunnel has become one of the major problems to be solved in geotechnical engineering.Sin ce the development of soft rock support systems,the setting of reserved deformation has become one of the conventional methods.To a certain extent,the setting of reserved deformation ensures that the support will not invade the limit.However,If the set reserved deformation exceeds a certain value,it will lead to overexcavation of surrounding rocks and increase construction costs.Therefore,during the construction of soft rock tunnel,it is of great significance to study the excavation deform ation law of surrounding rock and the factors causing large deformation,determine reasonable reserved deformation,fully exert the bearing capacity of surrounding rock,optimize lining structure and guarantee the stability of tunnel chamber.At present,the setting of reserved deformation is often determined by referring to relevant specifications or engineering analogies,lacking certain theoretical methods.So this article proposes a method for determining the reasonable reserved deformation of weak surrounding rock based on elastic theory,elastic-plastic theory,and viscoelastic theory,and the following research results have been obtained:(1)On the basis of elastic theory,the displacement expression of surrounding rock considering the reserved deformation m under the non axisymmetric condition,the expression of determining the optimal reserved deformation m0 of surrounding rock in the elastic state,and the exp ression of support resistance related to surrounding rocks,support materials and in-situ stress are derived.The displacement expression of surrounding rock and the optimal reserved deformation expression were programmed using Fish language by FLAG 3D software,and th e relevant numerical results were solved.The results of the numerical solution and the analytical solution were compared,and it was found that the error between the two was relatively small.(2)According to the classical elastic-plastic theory,the displacement expression of surrounding rock considering the reserved deformation m and the expression of the optimal reserved deformation m0 under the condition of non axisymmetric load,as well as the support resistance expression reflecting the strength of surrounding rock,the strength of support materials,and the size of crustal stress,are derived through the approximate solution.The numerical simulation software was used to simulate the displacement expression of the surrounding rock considering the reserved deformation m and the expression of the optimal reserved deformation m0 under non axisymmetric load conditions.Comparing the results of numerical simulation with those of analytical solution,it was found that the error was within 12%,which shows a good consistency.(3)According to relevant theories of Burgers model and referring to the ideas by previous researchers,an analytical solution of the Burgers model considering the support effect was derived.Based on this analytical solution,the displacement expression of the surrounding rock considering the reserved deformation m and the expression of the optimal reserved deformation m0 under non axisymmetric load conditions were derived.The FLAC 3D numerical simulation software was used to numerically simulate the two expressions,and the results showed that the error between the numerical simulation results and the analytical solution results was within 10%,indicating good consistency.(4)Comparative analysis was conducted on the analytical solutions of surrounding rock in different states from the perspectives of accuracy and practicality.Based on the support scheme of the soft rock support test section of Lianchengshan Tunnel,three analytical solutions for the displacement of surrounding rock under different support schemes were obtained and compared with actual monitoring data.Through comparative analysis,it was found that the error between the elastic solution and the monitoring data is relatively large,while the error between the elastic-plastic solution and the viscoelastic solution is basically within the range of 15%,and the viscoelastic solution is more accurate than the elastic-plastic solution. |
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