Numerical Simulation Method Of Macro-Mesoscopic Failure Process Of Post-Peak Rock Mass And Its Application

With the rapid development of China’s economy, the demand for oil is growing. For our country, safe and stable supply of energy is the important guarantee of economic sustainable and healthy development. Therefore, accelerate the construction of underground tunnel is still the goal of the next five-year plan, which will mean an increasing number of rock project. The buried depth and more intense tectonic activity, the in-situ stress level is the higher; The possibilities and frequency are much higher that these projects happen deep engineering disasters such as continuous large deformation and large volume landslides under the action of the strong excavation unloading, and causing casualties, machinery and equipment obsolescence, part of the tunnel was forced to stop or relocate, serious environmental damage and huge economic losses. These disasters have seriously restricted the our country such as traffic, water conservancy and hydropower project construction and operation safety. Therefore, the analysis and research of deformation and destruction process of the fractured rock mass for long-term stability of the tunnel running plays a very important realistic engineering significance, social significance.Rock can be assumed to be a kind of inhomogeneous multiphase composite structure; After the external force, the micro-defects randomly distributed in the rock inside are constantly changing, appear through, cracks in the rock gradually formed macroscopic damage, Leading to instability of the rock structure. Rock post-peak stress is very complex and generally is in unstable state, its mechanical behavior is hard to be described with classical strength theory, and the brittle failure is assumed to be continuous media is there is a problem, is not correct. In this paper, Based on the result of indoor triaxial test, the failure and structural instability process of fractured rock are analyzed. In this paper, the main research contents include:1) Making up similar sandstone brittle material have been formulated for indoor conventional triaxial experiments of fractured rock mass and studying deformation and failure process of post-peak fractured rock mass from a macro perspective. These two aspects laid a foundation in the research of theory and numerical method; Then, the full stress-strain curve of fractured rock mass is obtained, and the influence of confining pressure and inclination on strength and deformation characteristics of the fractured rock mass have been analyzed.2) The macro-discontinuous deformation and failure process of post-peak fractured rock mass have been studied. The stress-strain curve obtained through indoor experiment is analyzed and the key point of failure process by structural rock is confirmed. Based on bifurcation and chaos theory, the peak point is defined as bifurcation point and the point of macroscopic crack coalescence is defined as failure point, then, The relationship between dimensionless parameter D and σ which use for analyzing the failure and structural instability process of fractured rock is obtained. Based on the Weibull distribution model, damage constitutive relation is put forward in which fractured rock is continuous media. The relation between parameters of rock damage softening model and confining pressure and inclination angle is discussed.; Based on energy conservation theory, Structural instable failure (discontinuous deformation) of fractured rock is analyzed; Based on the strain energy density theory, Damage and failure criterion of rock meso unit is established, and computer program for calculating deformation failure process of rock is developed by the FISH language in the FLAC D. In combination with results of indoor test, the simulation results verify the correctness and feasibility of the damage model and calculating program.3) Based on the manifold cover concept, construct the three-dimensional Manifold cover functions, In combination with the particle model, Manifold Discrete Particle Unit is built and a new discrete element numerical method has been proposed. Introducing the micro plane theory, tension and compression constitutive model are established respectively, deformation and failure overall process of post-peak fractured rock mass from a macro perspective is analyzed, and MDPM has been checked and verified combined with laboratory experiments on numerical methods.4) Based on using discrete element software YADE, from the mesoscopic to macro, deformation and failure process of concrete and rock mass etc is analyzed using particle discrete element method which is based on manifold cover concept and proposed in this paper. Size effect of rock and other brittle materials, tension and compression asymmetry of mechanical properties have been analyzed, and the unified solution of continuous and discontinuous deformation problems have been accomplished.5) Based on the China’s first large underground crude oil storage caverns, using particle discrete element method which is based on manifold cover concept and proposed in this paper, three-dimensional model for simulating deformation and failure process of 5# main surrounding rock mass is built, recreating the process of large deformation of the left cavern wall leading to collapse. With continuous deformation method, the deformation and failure location of chamber which is obtained by calculating is the same place.In this paper, the research content provides a new method for researching the deformation and failure process of rock mass and the underground tunnel surrounding rock supporting problem, and it has guiding significance for understanding all kinds of massive landslides, large deformation and their supporting role.