| The engineering response characters of the deep rock masses are obviously distinct from that of the shallow part because of its complicated mechanical environment, that mean high in-situ geostress, high temperature and extra-high hydraulic pressure. There are a lot of doubtful questions, such as rock burst, water inrush and gas burst, in the process of construction, excavation and operation in deep rock engineering. In order to avoid the burst geological disaster and reduce the harm to the people's life and the property, we have to do meticulous research in the mechanical characteristics of deep rock mass in the process of excavation. It is also essential to study the occurrence regularity of geological environment in deep rock, the load-unload mechanical behaviors of deep rock mass under the effect of high confining pressure, and the multi-filed coupling model. Deep rock mass has become one of the most important issues for many scholars and engineers, that is also a rigorous challenge for the current scientific research.Based on the research of the concept of "deep stratum" and "deep project", a large number of domestic document literatures about deep engineering have been gathered. Based on this, a preliminary analysis about the characteristics of geostress in deep stratum has been made referring the method of Hoek-Brown. Some regression analysis of the geostress in deep rock has been done, such as the distribution of the vertical geostress varying with depth, the distribution of maximum and minimum horizontal geostress varying with the depth and the distribution of the lateral pressure coefficient with the depth, etc. In addition, the distribution characteristics of the structural surface and the quadratic stress field in deep rock have been studied. The corresponding laboratory test plan has been designed for the paper.The typical Baishan marble rocks were obtained from headrace tunnel in Jinping II Hydropower Station lying on Yalong River and they were prepared as standard columniform specimens of 50mm in diameter and 100mm in length. A series of tri-axial tests under loading and unloading conditions are carried out by MTS815.03 rock mechanics test system for the marble samples. First, both conventional uniaxial and tri-axial tests under high confining pressure are conducted. The experimental results can provide scientific evidence for the design of tri-axial unloading tests. Second, tri-axial pre-peak and post-peak unloading tests are conducted under different initial confining pressure. The unloading mode is keeping axial stress and unloading confining pressure. The complete stress-strain curves and the rock sample failure characteristics are studied and compared between tri-axial compression and unloading confining pressure tests.In the theory of multi-filed coupling aspect, the permeability evolvement law of rock is studied from the point of stress and strain. The connection of the damage of rock mass with stress and seepage were analyzed. Take the relationship of the porosity and volumetric strain in elastic porous medium as a bridge, the stress-seepage-damage coupling model in the fracture process of deep rock was obtained. According to the geological condition of the deep-lying headrace tunnel in Jinpingâ…¡Hydropower Station and the related results from the laboratory tests, the excavation of the headrace tunnel in Baishan marble and the stress and deformation performance of the adjoining rock are analyzed by the finite element method. The conventional condition of the excavation process with support and the stress-seepage coupling condition are considered in the calculation. Some conclusions and engineering proposals are put forward through the comparative analysis in the last.
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