Study On Construction Mechanics Of The Bi-Arch Tunnel In The Soft Surrounding Rock

Based on the Xiaojinkou bi-arch tunnel engineering of the Guanghui(Guangzhou-Huizhou) highway, the thesis primarily studies the mechanics problem of the excavating and supporting during the bi-arch tunnel construction in the soft surrounding rock by the finite element method(FEM) calculation and the analysis of the field monitoring measured data.Combining the study characteristic and the current construction method of the bi-arch tunnel in domastic and aboard, the paper deeply study the three heading construction method and the benching tunneling construction method. Firstly, by the dynamical FEM calculation about the above two construction method, the paper analyses the stress field and displacement field of the surrounding rock and the axial force and bending moment of the steel framework, specially analyses the most important member-the central wall and obtains the stress pattern during the different construction working procedure. After comparing the two methods, the paper considers the benching tunneling method is better. At the same time, the thesis analyses the time-state curve of the axial force and bending moment of the steel framework and the axial force of the anchor bolt. The analysis results are compared with the results of the FEM calculation. Through the FEM calculation and the analyzing data of the field, the result is that the central wall mainly endures the vertical pressure from the structure transferring and its bending moment is relatively less and its position of the maximum value of the bending moment locates in the joint between the central wall and the steel framework. Finally, the thesis primarily sets up the internal force model of the supporting structure system in the bi-arch tunnel, namely, the distribution model of the surrounding rock's pressure, the internal force model of the steel framework and the axial force model of the anchor bolt, and these results can have the guiding significance to the design and construction of the similar tunnel engineering.