| The focus of coal mining in China has shifted to the ecologically fragile mining areas in the west,and surface environmental protection and ecological restoration has become a major scientific problem to be solved in this region,and water resources play a dominant role in solving this problem.Coal mining has caused significant changes in the overburden fracture field,seepage field and stress field,and the mined water resources formed by coal mining are an important part of the water resources in the region.Therefore,it is particularly important to understand the seepage pattern and fracture damage characteristics of fractured rock bodies,and to investigate the influence of fracture seepage size effect to solve the contradiction of coal-water co-mining and rational use of mined water resources.In this thesis,the mechanical characteristics of coal and rock and their internal pore and fissure development rules are investigated by using uniaxial compression experiments and acoustic emission system.The seepage characteristics of fractures at different dip angles and the dimensional effect of fracture seepage in rock masses were investigated by experimental and numerical simulation.The seepage of coal and rock mainly occurs in its internal fissures,and the seepage rate and permeability are mainly controlled by the geometry of the fissures and the external stress state.Under the action of different normal stresses and tangential stresses,the permeability of coal rock bodies containing fissures decreases with the increase of stresses.The influence of fracture roughness,fracture dip and fracture size is more obvious when the coal and rock are in a low stress state on the seepage characteristics.Different modes of stress action have a greater influence on rock bodies with laminated structure and non-homogeneity.Fracture damage is less when the fracture surface is subjected to normal stress.When tangential stress is applied,the fracture surface undergoes shear damage,which significantly changes the morphological characteristics of the fracture and thus further affects the permeability.5-15 MPa of tangential stress produces about 2-5 times more fracture damage than normal stress,with concrete about2.2 times,coal about 3.6 times and sandstone about 4.7 times.The degree of damage to the fracture surface under hydro-force coupling is inversely related to the strength of the rock mass.Under the action of hydro-force coupling,rock particles that are transported with water due to fracture damage are generated in the fracture,and when they are transported and filled into a certain area of the fracture,they will aggravate the fracture damage.Rock fracture seepage is affected by fracture dip and fracture morphology.When the angle between the fissure and seepage direction increases from 0° to 90°,its permeability decreases by 65% on average.And under the same stress state,the permeability of X-type and Y-type combined fissure seepage is higher than that of single fissure seepage by 2～3 times.Rock fissure seepage has obvious seepage size effect.There is a critical size for seepage,and when the size is reached and the fissure size continues to increase,the permeability of the rock fissure remains stable.The change in permeability with fracture size can be broadly divided into three stages,which are the significant change stage,the stabilisation stage and the stability stage.The study of the seepage characteristics of coal and rock provides some reference for achieving the conservation and utilisation of mined water resources.There are 66 figures,12 tables and 89 references in this thesis. |
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