Experimental Research On The Feature Law Of The Fracture Surface Of The Coal-Rock Combination

The fracture pattern of the bending failure of the layered rock mass above the mined-out area is the channel of the gas migration path and the area of gas enrichment.In order to obtain the fracture surface morphology characteristics of the bending deformation and failure of coal and rock,a rectangular composite specimen was prepared,and a three-point bending experiment was carried out to systematically study the influence of coal and rock strength differences and thickness differences on the fracture surface morphology.(1)The coal-rock combination test block with a size of 100mm × 100mm × 400m was prepared,and five thickness ratios(1:1,1:1.5,1:2,1:2:2.5,1:3)and five strength differences(5MPa,10MPa,15MPa,20MPa,25MPa)were designed with the method of pouring and natural stacking.(2)The three-point bending test of coal and rock combination was carried out,and it was found that the bending strength of the poured test block was about 1 to 2 times that of the natural stacked test block under the same conditions,and the stress-strain curve presented double peak characteristics.The fracture surfaces of rock combinations on both sides of the interface show the characteristics of horizontal migration.(3)A method of network division of the fracture surface and three-dimensional reconstruction using SOLIDWORKS software is proposed,and the distance,angle and angle change of the transverse and vertical contours of the fracture surface of the test block from the central plane are extracted for the fracture surface Quantitative analysis.(4)Using the measurement and analysis function of SOLIDWORKS software,the specific values of the two characteristic parameters of distance and angle are obtained.The distance characteristic parameters show that when the coal-rock combination is bent and damaged,cracks are randomly generated from somewhere below and gradually move toward the loading point.Close;the angle characteristic parameters show that the degree of change of the fracture surface of the cast coal-rock assembly is smaller than that of the natural stacked test block,and the degree of change of the fracture surface will decrease with the increase of the thickness difference.(5)Using the ABAQUS software to simulate the bending failure process of the coal-rock assembly,the bending failure characteristics of the coal-rock assembly are analyzed.When the crack extends to the interface of the coal-rock assembly,it will migrate horizontally along the interface,and the crack tip appears at this time The phenomenon of local stress concentration;the increase in the thickness of the underlying rock mass will weaken the phenomenon of local stress concentration.The mixed failure mode dominated by shear stress is the key factor leading to the horizontal migration of cracks.Through laboratory experiments,numerical simulation and theoretical analysis,the mechanical characteristics and fracture surface morphology characteristics of coal-rock combination under bending failure are obtained.The research results have important guiding significance for the analysis of overlying fissure development.Figure[326]table[68]reference[100]...