Seepage Evolution Mechanism Of Deep Buried Jointed Rock Mass And Its Engineering Application

Along with some strategic plans such as development of western areas continuous puts into effect, the focus of tunnel, water resources and hydropower engineering construction is gradually shift to the west. But in the west karst area water disaster frequently appears, and the problem of water bursting becomes one of major disasters restricting engineering development. The seepage evolution mechanism of rock mass is the basis to study water bursting. As rock mass has experienced the long-term geological process and human disturbance effect, various defects such as joint had bred internally. Therefore, study aim at the seepage evolution law of jointed rock mass under different stress state has great significance to mechanism discovering of water bursting and prevention and control of underground engineering.In this paper, deep buried jointed rock mass was regarded as research object, basing on the combining method of physical simulation experiment, theoretical analysis and numerical simulation, a series of studies on the seepage characteristics of rock mass under different ground stress state and hydraulic pressure has carried out, which have certain guiding sense to the construction of related projects and water bursting prevention.(1) A new physical simulation test system on large-scale rock mass seepage was developed, which could come true multi-direction load. It includes main bearing device, ground stress servo loading system, gas-liquid composite confined water loading system and other auxiliary equipment, whose maximum ground stress load is 6.0 MPa, hydraulic pressure load is 2.0 MPa and model body size is 300×300×1800mm. Fluid-solid coupling similar material is also made up which is skilled in osmotic adjustment. New test equipment, test material and related method were provided to uncover the seepage evolution mechanism of underground rock mass under complicated stress state.(2) By the seepage simulate test on the homogeneous rock mass model with different permeability, relationship of pore water pressure along with hydraulic pressure and ground stress is obtained. As the increase of diffusion distance, the pore water pressure of homogeneous rock mass under different stress state decreases gradually, this obeys hyperbola attenuation law. The expressions of maximum diffusion distance and the minimum thickness of protection layer were deduced, and the maximum diffusion distance and the minimum thickness of protection layer increased gradually along with the increase of hydraulic pressure and the decrease of ground stress. According to the differential form of Darcy law, a new method for calculating the internal hydraulic gradient of homogeneous rock mass is put forward, and by which the calculation result is more approximate to the actual seepage rule comparing with the traditional calculation method. Furtherly the influence law of stress state and material permeability with the hydraulic gradient of homogeneous rock mass is acquired.(3) In the basis of seepage evolution law of homogeneous rock mass, seepage simulate test on the rock mass containing a single nonpenetrating filling joint with two different width was proceeded to study the influence of hydraulic pressure, ground stress and lateral pressure coefficient to the seepage evolution law. Pore water pressure within the rock mass containing a single joint decreases gradually as the increase of diffusion distance, and which conforms to the logarithmic decrement law. The expression of hydraulic gradient within a single joint was deduced based on differential method. After comparison and analysis we can know that, the traditional calculation method to calculate hydraulic gradient is feasible to qualitatively describe the permeability characteristic of jointed rock mass, and the differential method can more comprehensively reflect the evolution process of internal pore water pressure of jointed rock mass.(4) After summarying and analysising the degradation effect of water to rock mass mechanics properties, the coupling calculation method both considering water osmosis and rock mass softening under the action is put forward based on the finite difference softwar e. With Liu Pan Shan tunnel as an example, the influence law of confined water pressure, the thickness of the protective layer and aquifer thickness to displacement, principal stress and the plastic zone distribution is mainly investigated to account for the stability mechanism of deep buried tunnel under the action of water osmosis.