| Tunnel anchorages are a common form of anchorage for suspension bridges,and their construction methods are similar to tunnel construction.Tunnel anchorages are different from conventional tunnels in that their large inclination and variable crosssection structural characteristics make the deformation and stress characteristics of surrounding rocks more complicated.Due to the immature development of related theories and relatively few application of engineering cases,the stability of the surrounding rock during the construction of the tunnel anchorage is still very uncertain.The selection and specific application of the construction method during the excavation and support process are also need to be studied.Therefore,this dissertation focuses on the analysis of the choice of excavation and support methods for tunnel anchorages and the deformation characteristic and stress characteristics of surrounding rocks during construction.It not only provides guidance for the construction of the project,but also provides a certain reference for similar project design and construction.In this dissertation,the tunnel anchorage of the north shore of the Wujiagang Yangtze River Bridge in Yichang City is used as the engineering background,and the excavation methods are compared and selected using the Hierarchical Weighted Decision Analysis.The FLAC3 D finite difference software is used to carry out numerical simulation calculations to determine the rationality and accuracy.The stability of the surrounding rock during the excavation and support process was analyzed according to the quality of the rock surrounding the tunnel anchorage and the characteristics of the large inclination and variable section,and the numerical simulation calculation was performed to evaluate the stability of the surrounding rock.The deformation characteristic of the surrounding rock during the tunnel excavation and support process is analyzed based on the on-site monitoring and measurement data,and compared with the results of numerical simulation analysis to verify the accuracy of the numerical simulation.Finally,some parameters of the three-step temporary invert actually selected are optimized and analyzed.The main conclusions of the study are as follows:(1)Among the four tunnel anchorage excavation methods: the step method,the three-step temporary inverted arch method,the positive step circular excavation method,and the CRD method,considering the deformation and settlement during construction,the engineering cost,the construction difficulty,and the construction speed,the three-step temporary inverted arch method is superior to other methods.(2)Analysis of on-site monitoring measurement data and numerical simulation results show that after the tunnel anchorage is excavated,the large deformation is located in the weak weathered layer of the tunnel entrance and the lower part of the tunnel anchorage,and it is necessary to strengthen the support of the site;The plastic zone only exists in a small local area,the arch top forms a lower compressive stress area,and the floor and side walls form a tensile stress area.According to the distribution law of the stress field,displacement field and plastic zone of the surrounding rock,it can be determined that the condition of the surrounding rock is relatively stable.(3)Based on the convenience of construction and the length of the support closure period,the step length of the three-step temporary invert is determined to be 4.8m ～6m,and the excavation length is determined to be 0.8 ～ 1.2m.The second lining time of the saddle section is suggested to be 27 d after the excavation of the entire saddle section;the second lining time of the rear anchor section is recommended to be 17 d after the excavation of the rear anchor section,and then the anchor body casting and the secondary lining of the front anchor section are sequentially performed. |
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