Research On Risk Evaluation And Countermeasure Of Rock Burst In Deep Buried TBM Tunnel Constructed In Plateau Region

Since the 21 st century, the general development tendency of tunnel engineering is “long length, heavy section, great buried depth” in our country. The stability of surrounding rock of subterranean tunnel makes a very direct effect on the success of subterranean engineering, and rock burst is one of the important geological disasters in large-scale subterranean engineering. Rock burst in deep buried TBM(Tunnel Boring Machine) tunnel constructed in plateau region was the object of research in this thesis, and the mechanics tests of schist were conducted to obtain the mechanics parameters. The regularities of in-situ stress field and induced stress field were analyzed theoretically. Then, by using theoretical method and BP neural network theory, the risk evaluation of rock burst of surrounding rock in the research area were carried out respectively, and the countermeasures of TBM tunnel constructed in rock burst section were put forward based on the indoor results acquired above. Thus, the research on risk evaluation and countermeasure of rock burst of TBM construction had great guiding significance and practical value, which could help any problems were spotted early, reduce the loss caused by rock burst, and provide the basis for the planning and design of the downstream of Yarlung Zangbo River. The detailed work and findings of this thesis are as follows:(1) The results of conventional triaxial test indicated that surrounding rock had a great influence on axial pressure and the peak strength of axial pressure could be improved considerably by the surrounding rock. The results of unloading confining pressure test showed that stress-strain process consists of four stages, which includes elasticity, yielding, brittleness and plasticity, and the yielding stage was obviously showed in the stress-strain curve. Moreover, by analyzing the different states of unloading rate, we could easily draw the conclusion that over-quick unloading rate would lead to the accelerated destruction of sample.(2) According to the analysis of in-situ stress field and induced stress field, the research area in this thesis belonged to high initial stress area, and the maximum principle stress was about 80 MPa. For principal stress, it would increase with increasing buried depth. In addition, the characteristics of in-situ stress field of research area were simulated and analyzed numerically based on FEM(Finite Element Method). The simulation results showed that the maximum principle stress of tunnel axis was 76 MPa, and it would reduce 10 MPa near fault because of the influence of fault. Then, the spatial distribution characteristics of induced stress field under the buried depth of 2000 m were analyzed to draw the conclusion that the occurrence position of rock burst may be affected by the stress difference, and the area that was from the tunnel face to the position, which was far from tunnel face 2 times diameter of tunnel, was the place where the rock burst frequently occur.(3) With the application of strength criterion and energy criterion, rock burst occurrence in the research area was evaluated, respectively. The results indicated that weak and middle rock burst were the main rock burst forms in this area, but it was potential that the occurrence of strong rock burst in partial area. Moreover, the rock burst proneness was predicted and evaluated by applying BP neural network theory, and the evaluated result was basically in concordance with the result of criterion.(4) The origin of rock burst depended on two key and vital factors consists of stress condition of tunnel and trigger of construction. The countermeasures were put forward based on the characteristics of rock burst in this area. The construction scheme of control in the first place and integrating prevention with control should be adopted for the rock burst. Meanwhile, as the area, which is far from tunnel face 2 times diameter of tunnel, had frequent occurrence of rock burst, the formulation of countermeasures should be considered from supporting measure primarily. Effective and timely support could not only improve the value and distribution of initial stress, but also made the stress state of rock mass around the tunnel from plane stress to spatial three directions stress. Supporting measure should be enhanced to reduce or avoid the occurrence of rock burst in this area.