| It is problem to be solved urgently that revealing coupling mechanism of stress-fracture-seepage in excavation coal-rock for researching on rock mechanics and mining science.There exists complex geological conditions of steeply inclined coal seams including large dipping angle and thickness of the seams including large dipping angle which reaches 87 degree,and high thickness with 50m maximum of the seams.High in-situ stress is enriched in coal-rock of steeply inclined under the effect of historical tectonic movement,which would be released during repeated mining and may easily induce coal-rock dynamic disaster such as roof falling,gas emission and water inrush etc.The common scientific problem is coupling relations of stress,fracture and seepage fields in coal-rock.Hence,a study aiming at revealing coupling mechanism of stress-fracture-seepage in coal-rock was carried out in this work,by means of theoretical analysis,laboratory experiment,physical simulation model building,and engineering practice etc.(1)Based on the background related to the research of steeply inclined coal seams mining,a study on precise identification of fracture parameters and fractal features has been carried out.Correlations of fracture length,numbers and fractal dimensions have been analyzed.The results show that relation of fracture numbers and fractal dimension is a positive correlation.However,relation of fracture average length and fractal dimension is an inverse correlation.The larger number of fractures and the larger fractal dimension.The longer fracture average length and the smaller fractal dimension.Furthermore,CT values of fracture feature pixels have been analyzed by comparing different CT slice images.X-ray attenuation degree of rock materials is obviously higher than coal materials.(2)Experimental research on coulping relations of stress-fracture-seepage in excavation coal-rock has been developed.Seepage behavior is vividly shown during coal or rock specimens crack process by injecting imaging liquid.Also,imaging liquid injecting dosage quantitatively reflected fracture seepage capability.Therefore,acoustic emission(AE)data,fracture dynamic evolution and seepage images have been achieved under multi-level cyclic loading in the laboratory experiment system integrating X-ray digital radiography technology,AE testing and infrared radiography.The results show that fatigue damage cumulative strength(FDCS)of coal sample under multi-level cyclic loading is 14.03MPa.FDCS of rock sample is 15.83MPa.Average felicity ratio of coal specimens is 1.12 and rock specimens is1.41.Failure process of coal and rock specimens under multi-level cyclic loading defined as the process of fracture extending,fracture closing together and main fracture structure failure.Fracture seepage behavior in coal and rock specimens show typically non-liner evolution laws.Stress-fracture-seepage behaviors of coal and rock show closely coupling properties.(3)Physical simulation experiment study was conducted on coupling-induced disaster mechanism of stress-fracture-seepage in top-coal caving of steeply inclined coal seams.It was studied and revealed co-deformation mechanism of ground and underground stratum during coal seams excavation,and fracture seepage behavior responding to groundwater flow system.Experimental results show that co-deformation essence of ground and underground stratum during coal seams excavation was fracture extending due to roof shearing and sliding.Fracture evolution was mainly shown in the location of roof and rock pillar.There is an essential control effect on structure evolution of surrounding rock from rock pillar stability.Responsing mechanism of groundwater flow system was also studied and revealed.Space between separated layers could be enriched with water and then underground water flows into mined-out area.Water hydrocele could flow from the mined-out area of 43#coal seam to the mined-out area of 45#coal seam,and then flows into floor of coal seam in the way of seepage behavior.Space transfusion features is astern replenishment and lateral providing.(4)Mechanism of dynamic diasaters evolution has been revealed according to coupling relations of stress-fracture-seepage during steeply inclined coal seams mining.Furthermore,in-situ stress field type is?_H>?_V>?_h for considering detection results of stress field,fracture field and seepage field.The detection results show that fracture development in coal seams of87 degree is richer than that in coal seams of 45-degree,and which show obviously shearing failure feature.The critical depth of steeply inclined coal seams deep mining is 365m to 410m.Space relations model of large-scale fracture in the ground surface and working face was established.The O-style collapse in the ground surface extends to formating V-style collapse groove along the working face heading and horizontal direction as the deeper mining.(5)The engineering application effect shows that Markov chain model and probability transition matrix could scientifically describe coupling-induced disaster process of fracture-seepage in excavation coal-rock.These states that dynamic disaster prevention should be placed by an emphasis on stability control of roof and rock pillar.The in-situ monitoring data proves that the possibility of coupling-induced disaster has been lowered by taking measures for ground deep borehole blasting of steeply inclined rock pillar and prevention technology is reasonable and effective against dynamic disasters.These research results provided scientific basis for dynamic disaster prevention in top-coal caving of steeply inclined coal seams,which could also provide some significant guidance for safety mining of complicated coal and rock. |
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