| As a permanent underground building,the tunnel should not only ensure the stability of surrounding rock during excavation,but also require the additional force that can resist the long-term creep of surrounding rock.In engineering practice,some tunnels are subjected to the creep of surrounding rock,resulting in excessive deformation and lining cracking,which have a negative influence on the long-term stability of the structure.Therefore,it is an important task to analyze the load transfer law and the deformation characteristics of the supporting structure under the creep condition of the surrounding rock from the mechanical point of view.The Loess creep model is built based on the indoor test,and the concept of Surrounding-Reinforcement is introduced,based on witch the mechanical model is established.The load transfer law under the creep condition of loess is obtained,and a reasonable calculation model is established to calculate the lining internal force and to realize the stability analysis of the lining.The main research results are as follows:(1)The creep characteristics of Q3 loess of Tang Jia Yuan under different stress and water content are analyzed through the indoor soil test.According to the test results,the Burgers model is chosen as the creep model of loess and the mathematical model is used to analyze the model parameters and the law of variation with water content.Finally,the rationality of the creep model is verified by comparative study.(2)The tunnel is analyzed by visco elastic plastic method basing on the concept of Surrounding-Reinforcement,under the condition of considering the dilatancy of surrounding rock.In the above research process,the parameters of Surrounding-Reinforcement are determined firstly,and then the law of load transfer and deformation and failure of surrounding rock under creep condition are obtained based on the modified Burgers model.(3)The Load-Structure method is used to calculate the internal force of lining taking ellipse as the fitting curve of the lining section of arch tunnel.In the course of analysis,the form and range of elastic resistance distribution are solved based on iteration method,and the iterative transfer coefficient is introduced to simplify the iterative process and realize the accurate and fast calculation of lining internal force.According to the calculation result of internal force,the worst position of lining stability is obtained,and the key area of lining stability evaluation is obtained,which provides basis for lining stability evaluation.(4)Taking Tang Jiayuan tunnel as an engineering background,the creep characteristics and influencing factors of tunnel surrounding rock are analyzed,and the long-term stress characteristics of the tunnel support structure are analyzed.The theoretical and experimental data are compared and analyzed to verify the correctness of the theory.At the same time,the long term stability of the tunnel under the existing supporting condition is analyzed,and the problems are pointed out,and then put forward reasonable design proposals.The load transfer law of support structure under creep condition of loess is studied and put forward the concept of support design:In the weak stratum,the initial support ensures the safety of the tunnel during the construction stage,and bears the additional stress caused by the creep of the surrounding rock with the secondary lining.Ensure the stability of the support structure in the whole operation period of the tunnel,and pay attention to the coordination between the initial support and the secondary lining support strength.The research results have important theoretical and practical significance. |
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