| Underground reservoir is a key technology for co mining coal and water resources in ecologically fragile mining areas in the west and an important component of the development and utilization of mined water resources.When using coal pillars as dam bodies,it is subject to mining disturbance and weakening of mine water infiltration during service.Its long term stability is one of the urgent scientific issues to be solved.It is difficult to restore the mechanical and seepage characteristics of coal and rock mass under the three dimensional stress environment of underground space under uniaxial or conventional triaxial test conditions.Therefore,a true triaxial rock mechanics test platform has been developed.By studying the mechanical properties and failure mechanisms of coal samples under true triaxial compression with different intermediate principal stresses and true triaxial loading and unloading with different stress paths,as well as the distribution characteristics of three dimensional microscopic pore structure and the law of pore seepage under different seepage pressure and velocity differences,the numerical simulation analysis method for long term stability of coal pillar dams is optimized to provide reference for the design of underground reservoir coal pillar dams.True triaxial mechanical tests show that coal samples have significant“intermediate principal stress intensity effect” and “intermediate principal stress failure effect”.Among them,the peak strength and peak strain of coal samples in the true triaxial compression test first increase and then decrease with increasing,and the failure pattern presents a transition of shear fracture + associated crack,single shear failure,tensile failure + shear crack;The larger the true triaxial loading and unloading test is(during unloading),the higher the failure rate of the coal sample is,and the more macroscopic cracks are developed.Moreover,the macroscopic fracture surface of coal samples under true triaxial conditions is always parallel to the fracture surface at the time of failure,revealing the fracture evolution mechanism of coal and rock masses in underground space under triaxial stress and disturbance.The failure mechanism of coal samples under true triaxial test is also applicable to conventional triaxial test,because the sample in conventional triaxial test is approximately in true triaxial state before failure.The Mohr-Coulomb and Mogi-Coulomb strength criteria are applicable to rock failure under the two conditions,respectively.The fitting cohesion and internal friction angle are consistent.The pore data of coal samples were obtained through CT scanning,and the pore fracture network structure and pore throat equivalent parameters were analyzed using three dimensional reconstruction.The results showed that the main fluid seepage channels were the main fractures and the cleats connected thereto,and the porosity and permeability of the coal sample were obtained.Based on the pore network structure scanned by CT,a numerical model was established to study the seepage law of mine water under different flow velocity differences and pressure differences.It was found that the average pressure of each section along the infiltration direction decreased approximately linearly,and the average flow velocity was negatively correlated with the surface porosity.In areas with small pore radius and good connectivity,the flow velocity increases significantly;In areas with small pore radius and poor connectivity,the pressure increases significantly.Based on triaxial tests,an H-B strain softening model was successfully established and validated in numerical simulation software.At the same time,a long term stability study of the coal pillar dam under the action of fluid solid coupling fields was conducted,providing a reference for the design of the width of the coal pillar dam of the underground reservoir in the western mining area.There are 69 figures,11 tables,and 99 references in this thesis. |
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