Study On The Stability Of Adjoining Rock And The Liner Structure Of The Tunnel Under The High External Waterpressure And High Geostress

In the latest tens of years for meeting with the economic and social double-quick development, a great many tunnels used in a variety of fields have been built in the world. The trend of tunnel construction is more and more long-deep. In the process of construction, some special geological hazards will be met because of the great depth and long distance, such as high external waterpressure, watergushing, high geostress, rockburst, high geotemperature and nocuous gas and so on. These geological hazards become the main restricted factors of tunnel construction.The four diversion tunnels of Jinping Cascade 2 Hydroelectric Power Station is 16.625 km long averagely and 2525m deep in maximal bury-depth. In the construction region the maximum of principal geostress reached 54Mpa. The region belong to high geostress area. In the preceding excavation of 4km long exploratory tunnel, several bigger flows had taken place. The maximal flux approached 4.91m3/s and the maximal water pressure is 10.22MPa. There are few great depth, high external waterpressure and high geostress tunnels engineering and few researches on this up to present. Thus, there will be many challenges in construction of the tunnels.Based on the modern design theory of tunnels construction that the adjoining rock be regarded as primary load-bearing structure, this thesis have made researches on the stability of tunnels mother rock and the safety of support pattern under the high external waterpressure and high geostress. Firstly, the problem that external waterpressure aroused by different seepage control is how to sound distribute between the grouting rock and liner is analyzed by nonlinear computation. Secondly, grounded on the study of the distribution of the high external waterpressure and high geostress and the characteristic of the rock in engineering area, the paper built the elastoplastic FEM numerical simulation model, and think over the procedure in tunnels excavation and the history of work of water load, and then get the relations between the different tunnels diameter, different permeability coefficient and depth of the grouting rock and the deformation, stress distribution and plastic range of the surrounding rock and support structure. Finally, according to the modern design theory of tunnels construction, the particular design of country rock reinforcement and support structure are researched and presented for diversion tunnels. In addition, this paper carry out successfully the support design practice in the preceding excavation of 4km long exploratory tunnel.According to the thesis research results, the following conclusion can be drawn. If the grouting rock can possess sound anti-seepage capability and the liner structure canhold higher hydraulic permeability relatively, and if the adjoining rock can be made as primary load-bearing structure by construction measure, the stability of country rock and the safety of liner structure will be guaranteed.