Optimal Arrangement Of Bolts In Large-Section Tunnel In Soft Rock

With the development of expressway and high-speed railway, the construction of tunnels with large section will be an important part of tunnels in expressway and high-speed railway.However, neither a mature tutorial nor an available specification and less experience in design and construction can be consulted in construction of the large-section tunnels. Compared with the constructed tunnels before, there are a lot of difficulties in large-section tunnels. Moreover, geological conditions and features of geomaterial are complex; the design and construction of large-section tunnel are still on the phase of immaturity.In the thesis, the large-section tunnel in soft rock is investigated. Under the guidance of the basic principle of rock mechanics and NATM, taking the adjacent rock displacement and plastic zone as basic criterion, finite difference simulation model is established for different bolt arrangements in the same rock class tunnel section excavating by stepped method. During calculating and analyzing of numerical simulation by Fast Lagrangian Analysis of Continua (FLAC), the rock-structure mode is adopted, which is better and more reasonable than the conventional mode in tunnel design. In the analysis, the interaction of surrounding rock and structure is paid attention in order to consider the bearing capacity of rock sufficiently.By analyzing the results of simulation model,the stress distribution of large-section tunnel, the working stress of blots and the displacement of wall rock under the conditions of different bolt arrangements. Accordingly, a set of safer and more economic scheme of blots layout in large-section tunnel is obtained, and the design parameters are decreased and reasonably selected. The relevant conclusions of this thesis can be reference for large-section tunnel and underground structure's bolt supporting parameter optimization and amendment of the technical specification of large-section tunnel design and construction.