Mechanism And Prevention Technology Of Coal Bumps For Highly-stressed Coal In Deep Mining Under Dynamic Disturbance

Coal bump is a phenomenon which release the stress stored in the rock intensely, accompanied by sudden, sharp and violent destruction of coal and rock mass. Amounts of coal bumps in China becomes more than ever since the mining depth and strength are increasing and the geological structures in the underground are more complex. For deep mining in coal mine, high stress and strong disturbance are the two main factors. So the study of coal in a high stress environment and response to perturbations of coal in different states is important for dynamic hazard analysis. In this dissertation, mechanism and prevention technology of coal bumps for highly-stressed coal in deep mining under dynamic disturbance is studied deeply in field research, laboratory experiments, theoretical analysis and numerical simulation method.Firstly,by investigating coal bump accidents in some typical coal mines, the behavior and predisposing factors of coal bump are analyzed. The investigation shows that the bump tendency of coal surrounding roadway and stope is strong. Because of high stress concentration, the coal accumulates a large amount of elastic strain energy. The stress perturbations by tight roof fracturing, fault activation, extractive activities, shooting, earthquakes and other lead to coal bump.Secondly,based on the above experimental data, the effect on the mechanical properties of coal by axial pressure, confining pressure, the initial elastic modulus, Poisson’s ratio, degree of homogeneity, size and other parameters is analyzed with RFPA2D-Basic simulation software. the acoustic emission and stress wave attenuation under different static stress levels and dynamic disturbance waveform are analyzed by RFPA2D-Dynamic Static simulation software. The mechanism and prevention technology of coal bumps for highly-stressed coal in deep mining under dynamic disturbance is studied deeply.Finally, under the engineering background of Tangshan Mine T2193 island face, the risk areas of coal bump in T2193 island face is monitored and evaluated by multiparameter technology.Summarizing comprehensive prevention principles of coal bump, relief holes technology is applied in T2193 island face of Tangshan coal mine. Specific research results are as follows:1.Physical and mechanical properties of coal samples with coal bump tendency from Xinzhouyao coal mine.Based on the above experimental data, the effect on the mechanical properties of coal by axial pressure, confining pressure, the initial elastic modulus, Poisson’s ratio, degree of homogeneity, size and other parameters is analyzed with RFPA2D-Basic simulation software.(1) With the increase of confining pressure, the performance of coal and rock deformation of brittle failure under low confining pressure to plastic failure high confining pressure transformed features. With the increase of confining pressure, compressive strength, peak strain, residual strength increases. With the increase of confining pressure, coal damage threshold required for the degree of damage is constantly increasing.(2) The initial elastic modulus has no significant effect on the compressive strength of coal.The initial elastic modulus greater, the smaller is the peak strain. The initial elastic modulus of rupture did not affect the degree of damage threshold and the strain coal is smaller reaching the threshold when initial modulus is greater. Under the same strain, dissipated energy and elastic energy storage limit of coal samples with large initial elastic modulus is lower.(3)With the increase of Poisson’s ratio, elastic energy storage limit increases and dissipated energy decreases.(4) Compressive strength and degree of homogeneity of coal were negatively correlated. With the increase of the degree of homogeneity, compressive strength increasing trend has been reduced. Under the same strain, strain of large homogeneous coal sample is smaller and it reaches the damage threshold more easily, the more energy is released when the coal is destroyed. With the increase of the degree of homogeneity, elastic energy storage limit increases and dissipated energy decreases.(5) Changing the size had no significant effect on the compressive strength of coal specimen. The peak strain of coal samples with smaller size is smaller. With the increase in size of coal, residual strength increases. Equivalent elastic modulus and volume of coal samples was negatively correlated. With the increase of the size of coal, storage elastic limit increases. The size of coal has no significant effect on the dissipated energy.2. Fissures, the acoustic emission and stress wave attenuation under different static stress levels and dynamic disturbance waveform are analyzed by RFPA2 DDynamic Static simulation software.(1)The effect of dynamic disturbance on the injury mechanism of coal with high stress is discussed. The more elastic energy accumulated of coal with higher stress, the higher the degree of damage. When stress wave passes through the coal with higher stress, more cell is damaged, fissures is developed increasingly and the loss of energy and reduction the degree of stress wave are more.(2) Under stress wave disturbance, Coal samples with larger confining pressure are more difficult to be damaged, degree of damage is lower and fissures is less obvious. The loss of energy and reduction the degree of stress wave is less.(3) The greater wave crest and the wavelength are, the more serious damage to the coal. The loss of energy and reduction the degree of stress wave are more.(4) The compressive strength of coal with more damage is smaller. Modulus of elasticity and the degree of damage was negatively correlated. The degree of damage has no significant effect on to the coal peak strain. Storage elastic limit of coal samples with more damage is smaller.3. Based on dynamic damage constitutive equation of coal under static and dynamic loads, folding catastrophe model of coal system under static and dynamic loads is established. The mechanism and prevention technology of coal bumps for highly-stressed coal in deep mining under dynamic disturbance is studied deeply.4. Under the engineering background of Tangshan Mine T2193 island face, the risk areas of coal bump in T2193 island face is monitored and evaluated by multi-parameter technology.(1) The roadway in T2193 island face is monitored by electromagnetic radiation and cuttings amount. The monitoring data shows that the risk areas of coal bump is ahead of work face range 10 m to 50 m.(2) Based on FLAC3 d, abutment pressure peak is in front of T2193 island face 5m and 70 MPa with stress concentration factor of 4.67. Vertical stress superimposes at the intersection of work face and roadway. Abutment pressure peak is in front of T2193 island face 4.5m and 85 MPa with elastic strain energy of 374.9KJ/m3 Abutment pressure peak of pillar is 80~120MPa and elastic strain energy is 528.6KJ/m3.(3) With the mining disturbance load and roof fracture impact load increasing, the stress concentration of work face and coal pillar is greater. Stress concentration area spreads along work face.(4) Risk factor of coal bump is defined as min/WWke(28). Stress concentration at the intersection of work face and roadway is greater(k>1) and coal bump happened possibly.5. Summarizing comprehensive prevention principles of coal bump, relief holes technology is applied in T2193 island face of Tangshan coal mine.(1) After the excavation of relief holes in coal pillar, abutment pressure transfers to inside of the coal pillar. With the spacing of relief holes increase, the support pressure of work face decreases. The distance of concentrated stress area and roadway also increases.(2) With the deep of relief holes increase, pressure in pillar increases. The distance of concentrated stress area and roadway also increases. The increase of relief holes deep reduces the entity area in coal pillar. As a result, vertical stress and displacement will increase accordingly. So increase of relief holes deep weaken the risk of coal bump.(3) Vertical stress in coal pillars of work face under dynamic disturbance is 100MPa~120MPa and the elastic strain energy is 528.6KJ/m3.The distance of elastic energy accumulation region and roadway is 1.02 m. Vertical stress in coal pillars with relief holes is 80MPa~110MPa. Pressure relief holes lead to increase of broken region in coal pillars. With the entity area in coal pillar decreasing, the stress concentration region has increased and vertical stress is 110 MPa. Elastic strain energy reduced to 400KJ/m3 and the risk of coal bump is weakened.