Seepage Evolution In Rock Masses And Catastrophe Mechanism Of Water Inrush Under Liquid-solid Coupling Effect

Deformation, water hazard and other dynamic geological disasters often occur in tunnels resulting from the current trend that numerous traffic and hydropower tunnels will be built in deep underground, as well as the mining of deep minerals. In those deep underground engineering, one of the disasters which seriously threat the construction safety and delay the construction schedule is the water inrush, which is induced by the damage and permeability mutation in host rock under liquid-solid coupling effect. Therefore, the seepage evolution in rock masses and catastrophe mechanism of water inrush under liquid-solid coupling effect were investigated systematically by the combined methods of theoretical analysis, in-situ test, laboratory test and numerical simulation. The main conclusions can be drawn as follows:(1) A statistical damage model of rock based on Weibull distribution function and its parameter determination method were proposed according to the meso-scopic statistical damage theory, and then a permeability evolution model induced by meso-scopic damage of rock element was established. The permeability evolution in the stress-strain process of rock with different lithologies and structures was analyzed comprehensively using servo penetration test, accordingly, the mathematical model which shows the influence of damage-induced strain change on the permeability of rock was established, as well as the mathematical expressions of the critical impermeability deformation and strength. Two conceptual models of unweathered hard rock and soft rock were proposed to describe the relationship between the permeability and stress. And the determination methods of crack initiation points which correspond to permeability mutation were summarized.(2) In-situ water injection tests were applied for an investigation of the hydraulic properties of rock masses with different lithologies and rock structures, which show different permeability characteristics in intact rocks, fault zones and damaged zones. The conceptual model of P-Q curves obtained from water injection tests was proposed, the change of seepage state which transforms Darcy seepage to non-Darcy seepage was revealed. A formula for estimating the hydraulic conductivity of rocks under high water pressure was deduced using the test data in injection and observation boreholes and a relational conceptual model of the permeability evolution induced by water pressure was proposed. Combined analysis of test results and permeability evolution, a conceptual model of phase division seepage in rock masses under high water pressure was established, which was divided into initial seepage phase, connection initiation seepage phase, unsteady seepage phase and steady state seepage. Moreover, three seepage types of low pressure-induced seepage, high pressure-induced fracturing and the other type were considered from the relationship analysis between rock structure, integrity and hydraulic properties. As a consequence, the crack growth evolution within rocks under high water pressure was investigated. The catastrophe evolution process of water inrush and the seepage failure mechanism of host rocks were revealed using the above-mentioned models. Considering the unsteady seepage in rocks, a one-dimensional unsteady seepage analytical model was established. Comparing the calculated results by numerical simulation, the effectiveness of the analytical model was proved. The spatiotemporal evolution of pore water pressure and hydraulic gradient that can contribute to hydraulic fracturing was systematically investigated using this analytical model, so that, the catastrophe mechanism under unsteady seepage was further revealed.(3) A experimental system for water inrush induced by high water pressure and excavation was developed, and a similar material for liquid-solid coupling which is in accordance with mechanical and hydrological properties was compounded, based on the liquid-solid coupling theory and orthogonal design. Further study on the water inrush mechanism induced by seepage failure was done using the physical model tests, the influence of excavation and seepage on permeability characteristics was researched. Combining analysis of multi-field information and Acoustic Emission, the spatiotemporal evolution of crack within rocks under the excavation and seepage coupling effect was investigated, and the formation process of water-inrush channel and its microscopic mechanism were discussed.(4) The control effect of rock structure on permeability was investigated in view of the combined analysis of test results and theoretical analysis. The results revealed that a rearrangement of rock structure would occur by excavation, resulting in an increase in hydraulic conductivity and drop in impermeability. The damage zone and grouting circle were considered as the rock whose structure was artificial altered. In addition, a analytical formula for the pore water pressure distribution and inflow rate considering the damage zone or grouting circle was proposed, which was applied for an investigation of the influence and control effect of the rock structure on tunnel water inrush.