The Mechanism Study Of Coal Gas Compound Dynamic Disaster Induced By Coupling Instability Of Loaded Gas Bearing Coal-rock Combination Bodies

With the development of deep mining in recent years,the coal-gas compound dynamic disasters are aggravating day by day,which seriously threatens the safe production of coal mines.However,the research on the coal-gas compound dynamic disasters is still in the initial stage.It is urgent to study the mechanism of coal-gas compound dynamic disasters.In this work,the outburst-rockburst compound dynamic disasters are taken as the breakthrough point,and the gas-bearing coal-rock combination bodies which are seldom concerned in the past research are taken as the research objects.By means of experimental tests,theoretical analysis,physical simulation and numerical calculation,this paper explores the coupling catastrophic mechanism of coal-gas compound dynamic disasters induced by the damage in gas-bearing coal-rock combination bodies and gas seepage in coals.Some innovative results are obtained.The main conclusions were drawn as follows:(1)The permeabilities of Chinese anthracite coal samples with CH4 and CO2 were measured and analyzed.The results show that there are many similarities between the permeability of CH4 and CO2 in coal.Both permeabilities are controlled by adsorption expansion,effective stress and Klinkenberg effect.The stronger the gas adsorption ability or the greater the confining pressure,the smaller the permeability.Under the influence of temperature,the permeability of the two methods shows similar sectional characteristics with the increase of gas pressure,and the time required to reach thesteady state of seepage in the steady state permeability test also shows similar characteristics.As for CH4 and CO2,the effect of temperature on steady-state time is not prominent,and there are no clear trends.(2)The triaxial compression tests were conducted on gas-bearing coals and coal-rock combined bodies.The results show that the strength of the coal-rock combination body falls in between the single rock and coal,and the strength of coal-sandstone combined body is larger than that of coal-mudstone combined body.And the strengths of all specimens increase and ductile failure characteristics are much more apparent with the increment of confining pressure or with the decrease in the gas pressure and the elastic modulus shows a tendency of increase in general.Under certain conditions,the cracks produced from the failure of the coal part will also extend to the adjacent rock part.The strength characteristics of gas-bearing coals and coal-rock combination bodies all met Mohr-Coulomb criterion.The occurrence and propagation of cracks in coal and rock mass not only affect the macroscopic stress-strain characteristics of coal and coal-rock combination body,but also determine the permeability evolution characteristics.Under low confining pressure,the characteristics of the AE signals of the coal-rock samples are more similar to those of the coal samples.Under high confining pressure,the characteristics of the AE signals are more similar to the pulse distribution characteristics of rock.The AE cumulative counts and energy of the gas-bearing coal-rock body are higher than coal.(3)A series of tests of unloading confining pressure(UCP)under constant axial stress and unloading confining pressure-reloading axial stress(UCP-RAS)were carried out on gas bearing coal-sandstone combination samples.The tests revealed that the bearing strength and cohesion decreases,and the the internal friction angle increase under unloading conditions.Mohr-Coulomb strength criterion is also applicable to gas-bearing coal-sandstone combined bodies under unloading stress paths.Under UCP-RAS conditions,the coal part of combined body is more prone to deformation and fracture and the damage degree is more intense.The crack propagation is synthetically affected by gas deposit condition,mining induced stress and multiple stress paths.The AE cumulative counts and energy of the gas-bearing coal-rock body are highest for the UCP-RAS test,followed by the UCP test and the CTC test.(4)Taking the stress analysis at the contact surface of gas-bearing coal-rock combination body as a breakthrough point,the damage mechanism of gas-bearing coal-rock combination body is analyzed theoretically.In the process of damage loading,the additional interfacial stresses are generated on the contact surface between rock and coal due to the incongruous horizontal deformation.The additional stress of rock and coal is opposite,which controls the strength characteristics of coal-rock combined bodies.In the actual mining process,the main stress mode of coal-rock combination body is:with the increase of axial pressure,the compressive strength of rock at contact surface decreases but is still greater than that of coal far from contact surface.Meanwhile,the compressive strength of coal at contact surface increases but is still less than that of rock far from contact surface.The permeability evolution model of coal under the influence of gas-bearing coal-rock combination body is established and verified by laboratory data.Finally,a gas-solid coupling model of coal-rock combination body damage and gas seepage in coal is established considering the damage of coal and rock and the evolution characteristics of coal permeability under the influence of the combination structure.(5)The physical simulation experiments and numerical simulations of instability catastrophic of damage in gas-bearing coal-rock combination bodies and gas seepage in coals were carried out under different conditions.The results show that:after the occurrence of coal-gas compound dynamic disaster,both coal and roof will present a certain degree of deformation and failure;the most of the outburst coal and rock does not present obvious sorting characteristics.Gas pressure at the exposed surface is atmospheric pressure.From exposed face to the depth of coal seam,gas pressure rises sharply and reaches the maximum value at the stress concentration point,which is higher than the initial pressure of coal seam.Compared with coal and gas outburst,coal-gas compound dynamic disaster is more likely to occur under the conditions of relatively low gas pressure,relatively high coal strength and relatively low strength difference between coal and roof.However,it should be noted that these conditions can not meet the occurrence conditions of rockburst.The relative outburst intensity of coal and rock increases gradually with the increasing of gas pressure and stress.(6)Based on the research in the preceding chapters,the energy criterion of outburst-rockburst coupling dynamic disaster induced by instability of gas-bearing coal-rock combination body is established,and the mechanism of outburst-rockburst coupling dynamic disaster induced by instability of gas-bearing coal-rock combination body is revealed.The research results are analyzed and verified by typical cases in the field.We can thoroughly use big data technology and deep learing to give early warning for disasters.Meanwhile,it is necessary to adopt integrated prevention and control strategies by eliminating the gas internal energy and releasing the elastic energy simultaneously.