Damage Evolution And Rheological Behavior Of Deep Rock Mass Under Water-rock Interaction

Underground deep rock mass is in the complex environment of high in-situ stress, high temperature and underground water. Its deformation and failure characteristics have shown a significant rheological behavior. The deformation quantity of rock mass is increasing with time, causing the rock mass anti-destruction capability decline. At the same time, its components are changed by underground water through physical and chemical effects and hydraulic pressure. Besides, its microporosity generate, micro-crack propagating, damage aggravating, the cohesion and the friction coefficient smaller, macro-mechanical properties such as strength and stiffness declining and deform easier and the amount of deformation greater. The complex and specific environment resulted in the destruction of the rock engineering and personnel property damage.Therefore, the research of damage evolution and rheological behavior of the deep rock mass under water-rock interaction could provide scientific proof for the excavation,support and stability analysis of deep rock mass engineering, and had important guiding significance and good engineering value in the aspects of production safety, operation and engineering lond-term stability.This doctoral dissertation has been supported by National Natural Science Foundation of China (NO.50774093), Graduate Degree Thesis Innovation Fundation of Central South University (NO.134377237) and Jinchuan mining company significant science and technology project. Rock mass mechanics, rheology and damage mechanics theory has adopted to study damage evolution and rheological behavior of deep rock mass under the water-rock interaction from the field survey, the experimental research, the theoretical analysis and the computer simulation. The research work and achievement include the following aspects:(1) The geologic environment of deep rock mass at Jinchuan2#Mine had been known though the summary of data, the field work and on-the-spot measure. A mass of rock smples of different lithology were gained from850m、978m and1098m level of deep rock mass at Jinchuan2#Mine. A series of rock physical mechanics lab tests had been carried out in order to get fundamental physical mechanics parameter of rock samples. The result of tests showed that the mechanical property of the iherzolite and the clinopyroxene-peridotite exceeded in the Amphibolite’s and the marble’s, and the Amphibolite’s declined most obviously with the increase of the moisture content. So the amphibolite had been determined as the research object of water damage tests and rheological behavior in the later stage.(2) Several tests aiming at the amphibolite were done for damage evolution research with soak time on deep rock mass under water-rock interaction, including swelling test,ionic concentration measure test, microcosmic test of rock mass internal structure damage by electron microscope(EMS), mesoscopic test of rock mass internal structure damage based on nuclear magnetic resonance (NMR) technology and mesoscopic test of rock mass joint surface topography using advanced TalysurfCLI20003d laser surface topography measure instrument. The results of tests showed that the montmorillonite of rock samples occurred a series of physical and chemical reaction with water and led to rock mass damage.Besides,the free swell ratio,the NMR porosity,the joint surface topography characteristic parameter and the macro mechanical parameter had exponential decay function relation with soak time. And then damage evolution equation and constitutive relation of the amphibolite under water-rock interaction were established respectively by different damage variable according to the rock damage mechanics theory(3) The uniaxial multi-step incremental cycling loading and unloading creep tests of the amphibolite had been conducted with using the RYL-600shear rheometer both in nature drying condition and saturated water phase. And the strain-time curves of the rock samples under different stress were got from the creep tests. The experiment results showed that the rock samples had nonlinear viscoelastoplastic characteristics, including instantaneous elasticity, instantaneous plasticity, viscoelasticity and visco-plasticity.The deformation amount of rock increased continually with loading level and loading time. The rock samples showed obvious rheology. The underground water by water-rock interaction changed rock composition and structure, resulted in rock damage and reduced rock mechanic property, which dropt the creep threshold,increased the creep deformation amount, the creep rate and the stability time and aggravated the rheology of deep rock mass.(4) The T2relaxation time spectrum area and NMR porosity of rock samples at creep test could obtain with high effective and non-damage NMR technology.The results of the NMR image analyzing system indicated that the rock sample at saturated state had greater T2relaxation time spectrum area and NMR porosity, proved that water-rock interaction resulted in rock mass internal structure looser,rock damage aggravation and creep amount geater.The micropores and microcracks were consolidated with the increase of the external loading when the samples were at decay creep stage both in the natural state and in the saturated state,and the more the external loading,the less the T2relaxation time spectrum area and NMR porosity. The change rate of the T2relaxation time spectrum area and NMR porosity at different external loading in the saturation state was bigger.Because the rock sample had more micro defects,greater consolidation space and respond more strongly on the change of the external loading.(5) On the base of the results from the creep test and rock rheological mechanics theory, a new rock creep model had been put forward in this paper. The new model adopted the series and parallels of different linear elements of elasticity, viscosity and plasticity and the introduced nonlinear elements. It could simulate the behavior of decay creep, steady creep and accelerating creep at the same time. The parameters of constitutive equation of the new model had been confirmed though recognizing model parameters and processing the uniaxial creep tests results of rock samples under different stress. From the high consistency between the test and model curves, it could be known that the new model was suitable to describe the creep characteristics of the deep engineering rock.(6) The joint cracks random distribution network of rock mass was established by the monte carlo method.The random number had been produced with Visual c++programming,which could describe all kinds of distribution characteristics of the joint cracks. The finite element model was established, using ANSYS.And then, based on the established rock rheological model, to use the FLAC3D creep calculation module completed constitutive model of secondary development design through the application of fish language.The computer numerical modeling was done by FLAC3D to simulate the plastic yield state and loose circle dynamic expansion of deep surrounding rock at Jinchuan2#Mine under the water rock damage effect and rock creep in different supporting conditions. The results showed that the bolting system could decrease the deformation amount of the surrounding rock obviously.The underground water had an adverse effect to the tunnel’s long-term stability and increased its deformation amount.The length of the bolt had major influence on the supporting and was the best when the bolt’s free end was slightly greater than the thickness of the loosen zone According to the computer simulation analysis,the paper advised that the length of th bolt was3.0meter.