Study On Large Deformation Mechanism And Control Measures Of Soft Fractured Rock And Its Application For Carbonaceous Shale Tunnel

With the rapid development of the highway, railway and other underground engineering, the situation that the tunnels have to pass through surrounding rocks with high geo-stress, high residual tectonic stress, shallow bias, and fractured weak zone, will follows. Large deformation of surrounding rocks is a commonly encountered and high harmful geological hazard in this situation. As the tunnels pass through surrounding rocks with high geo-stress, high residual tectonic stress, shallow bias, and fractured weak zone, cumulative extension and plastic deformation with time-dependence is likely to occur. Conventional support techniques cannot effectively control the deformation, which may result into great difficulties in the tunnel construction. Collapse and intrude limit may happen if the treatment measures are not suitable. And then a lot of additional problems may occur such as damage of construction equipment, schedule delays, cost increase, etc.This paper is based on the Tianpingshan tunnel which lies in Guiguang railway and the Longtan tunnel which lies in Hurongxi highway. During the research, various means, such as laboratory test, theoretical analysis, and 3D numerical simulation, are used. In this paper the mechanisms of large deformation in tunnels with fractured weak zone are studied and mechanisms and mechanics behaviors during construction are analyzed. A comprehensive technology system for controlling large deformation is presented and a serious of useful research results are obtained.(1) Geological survey data in areas of large deformation with fractured weak zone are collected and analyzed systematically. Typical rock samples are collected and the triaxial compression and triaxial compression rheological tests are also carried out. According to the test curves, rheological characteristics of carbonaceous shale are summarized. And the viscoelastic plasticity strain softening creep mechanical model which can describe the overall creep process of black cat of the based engineering is established. Based on the one-dimensional constitutive equations, the three-dimensional constitutive equations of the model are deduced and 4 parameters of the model are decided. Parameters are identified using MATLAB, which is the experimental fundamental of the research of large deformation of surrounding rocks in tunnels with time effect.(2) By discussing the new definition of soft fracture rock mass, two characteristics, namely cumulative extension and time-dependence, are proposed. Five reasonable assumptions have been made on the large deformation theory and geometric field theory, Considering MR effect, the characteristic theory of large deformation has been expended. The analytical solutions of the tunnel surface displacement and the surface displacement rate have been obtained. Based on the project, three dimensional numerical simulation of large section tunnel construction process with soft fracture rock conditions, Considering rheological aging characteristics, targeted antecedent displacement, tunnel face displacement and the displacement behind tunnel face respectively, have been analyzed and discussed. The result shows that large antecedent displacement is likely to occure in front of the tunnel face, where double tunnel diameter away from tunnel face. The displacement of tunnel face accounted for 36% of the final total settlement. The extracted deformation of tunnel face caused by tunnel excavation is larger as the rock tendencies direction at an obtuse angle with driving directions than as the rock tendencies direction at an acute angle with driving directions. Calculated based on the results rheological, rheological deformation mainly concentrated at preliminary stage. The max deformation rate is 4.76mm/d, and the stable time is 60 days, which accounts for 25% of the excavation deformation(3) Based on the similar principal analysis of the goemechanical model test and the mechanical character test results of in-situ rock specimen, the geomechanical model test system is developed, which is used in the construction process of soften broken rock mass tunnel and the overload asymptotic process. The system is consist of similar material, triaxial combined model test-bed, non-uniform gradient loading system and multielement massage monitoring system. The newly low intensity axial compress creep equipment is developed and based on this, the axial compress creep character research on the developed similar material for soften rock mass is carried out. The large scale 3D combined model test steel structural rack and non uniform gradient loading hydraulic control system are developed. Based on the optical grating sensor technology, the multielement message parallel real time monitoring method which the nuclear is the optical grating system of full automatic information collection is established. With the self-developed high precision mechanical and grating ruler micro multiple points meters and the resistance strain collection system, the micro change signal and substantially fluctuate data of displacement and stress in the model can be monitored fully during the excavation and over load process, which solve the problem of information diversity made by monitoring method, apparatus and data processing software. By the check and computing, the main member of the model test system can fulfill the demand of intensity and stiffness, it can be used in the model test of construction process and progressive failure of rock mass in the condition of the same embedded depth and stratum.(4) The model test on construction process of soft fractured surrounding rock mass surrounding tunnel and overload asymmatic damage was carried out. During the test, the displacement changing law before the tunnel face is analyzed and the affecting range of radical displacement surrounding tunnel and the ultimate radical distribution laws were carried out according to the different anchoring condition. Based on the changing law of fixed section displacement with the excavation steps, the affecting range in depth during the construction process of soft fractured surrounding rock mass and the radical displacement changing laws of tunnel face were got. The squeeze deformation law of tunnel face is analyzed, and the test results and numerical simulation results are coincident well. The results can be guidance to the construction and design of the actual engineering.(5) Based on the laws got by theoretical analysis, model test and numerical simulations on the large deformation of soft fractured surrounding rock mass, through the summary of the deformation character of the soft fractured rock mass, the reason of large deformation is analyzed and the comprehensive technical on the large deformation during the construction of soft fractured rock is established. Based on the technical system, the control method is applied in the Tianpingshan tunnel which lies in Guiguang railway and Longtan tunnel which lies in the Hurongxi Highway and the well effect was got, which proved the practicability of the system.