| Mountain has a large proportion in China, which covers about2/3of the land area. With the fast development of land transportation in the country, mountain tunnels are more and more frequently used along railways and highways, some of which have to be designed to cross faults. And then large deformation, collapse and other problems were encountered frequently during the construction of the tunnels. These problems have important effect on the construction safety and progress, because the mechanical properties of medium around the faults are still unclear. As a special kind of soft rock, the wall rock around faults is influenced by temporal and spatial effect. Also, the tunnel’s primary support and secondary lining have their own mechanical properties which are partly unknown. So, the study on mechanical characteristics and optimization tunneling method of long tunnel that through fault zone is very necessary. In this dissertation, the mechanical characteristics and the optimization tunneling method of long tunnel though fault zone are studied, as a part of the Technological Research and Development Programs of the Ministry of Railways (No.2008G030-D) and High Altitude Low Atmospheric Pressure Railway Extra-long Tunnel Construction Key Technology Research (No.2009-17) Sponsored by China Railway Corporation. And the construction of9#inclined shaft working area of Guanjiao through fault zone as is taken as an example. The main content is as follows:(1) In the study of mechanical characteristics of tunneling in fault zone, the information of reconnaissance and design of9#inclined shaft working area were collected. The construction information is investigated including surrounding rocks, the groundwater and construction process. Base on the information, the criterion of surrounding rock classification for fault zone is proposed.(2) Base on the existing research, a new equation of displacement vs time and space which caused by tunneling through fault zone is brought out and calculation method for its parameters is proposed. The new equation is applied to the data of Guanjiao tunnel, and the results indicate that the equation and calculation method for the parameters reflect the temporal-spatial effect of tunneling. By the results, the characteristics of temporal-spatial effect of tunneling though fault zone were analyzed. The analysis result showes that the vault crown settlement and horizontal convergence cannot meet the code requirements for secondary lining installation due to the adjustment of equivalent modulus of wall rock in fault zone for longer periods, and that the development of horizontal and vertical release coefficient of displacement is not the same, and that the excavation has effects on the rock wall in2times of the excavation radius, which are in accordance with numerical analysis results conducted by others.(3) In virtue of the presented equation, the principle and optimization method for footage of the tunneling cycle is advanced and its applying condition is also analyzed. The footage of the tunneling cycle of Guanjiao tunnel through fault zone is optimized by using the proposed method. The practice proves that the method can be used to guide the engineering practice. The relationship between the footage of tunneling cycle and displacement of wall rock is also studied. The results indicate that:①When the distance is fixed, the longer length of the footage, the total vault crown settlement and horizontal convergence is smaller, while the level of rate of vault crown settlement and horizontal convergence was increased with the excavation footage, that is, the longer length of footage can reduce the total displacement and convergence, meanwhile, the risk of single cycle is increased. This also explains principle "short footage, quickly by" for tunneling in soft surrounding rock;②Maximum rate of vault crown settlement and horizontal convergence doesn’t necessarily appear behind the face of1times footage range. It generally appears behind the face between1times footage and1times hole diameter range.(4) In fault zone, the stress and forces in surrounding rocks, primary supports, steel arch, and bolt are investigated in situ. The results show that, in fault zone, the stresses in surrounding rock, primary support and steel arch at vault are much more than what in side wall and invert; excavation disturbance to surrounding rock is larger, where in the disturbance of upper section excavation is greater than the lower section excavation and the disturbance of lower section excavation is greater than the invert excavation.(5) The primary support with shotcrete and steel arch are equivalent to a complex as a unit and the steel arch part. Shortcrete is assigned as different parameters of unit respectively to carry out numerical simulation. By using the model of setting steel arch part and shortcrete as different parameters of unit respectively contribute to the understanding of force, safety evaluation and parameter optimization of primary supports. Based on the proposed optimization steps, parameters of primary supports of tunnel through F3fault were optimized. The practice show that optimized parameters in economy and actual operation is feasible.(6) Secondary lining stress was monitored in the field in fault zone. Secondary lining is affected by force and the development of contact stress of primary-secondary lining. The effect can be roughly divided into four phases, namely, fast growth phase, a stage of stable growth, stress adjustment phase and stable phase respectively. Flac3D software is used to build the numerical models in which the tunnel axis and the fault direction are orthogonal and the fault dip angle varies. Basing on the models, the characteristics of secondary lining force are analyzed and the law of force is summarized. In fault affected zone, the influenced range is within a certain range from the boundary of hanging wall and footwall. and the moment of secondary lining increases with the growth of dip angle of the fault. Also, while the axial force of secondary lining in the cross-sectional varies in different positions, the moment and axial force increase with the reduction of distance from the hanging wall and footwall. In fault rupture zone, influence range is about within a certain range away from the boundary of hanging wall. The moment of secondary lining decrease with the growth of fault dip angle, while the axial force increases, and they both decrease with the reduction of distance from the fault boundary. |
