Evolution Mechanism Of Energy With Roof-crack Process In Extremely Steep Coal Seams Under The Residual Coal Pillar

It is very important for the prediction of the dynamic hazards in extremely steep coal seams to study the evolution of energy with the roof-crack process.Revolving around the problems of energy evolution in roof failure,research sets the roof of extremely steep coal seams in Jiangou colliery as object of study.With hybrid methods including theoretical analysis,numerical calculation,physical model experiment and field monitoring,the research launched project of the energy evolution with roof-crack process under the influence of residual coal pillar,and the achievement will provide a scientific basis for site hazard prediction and prevention,the research results are as follows:Firstly,the theoretical analysis and numerical calculation of the energy evolution of roof of the steep coal seam was completed.The value of released strain energy being stored in the roof is obviously greater than the others,Excavation disturbance increase the damage of rock and releasing velocity of the strain energy increase remarkably due to roof-crack process.Under the influence of residual coal pillar,the character of energy distribution of roof before excavation is a fact that the energy increases gradually from the top to the bottom.With excavation of model,the characters of energy releasing at different positions is diverse,the maximum energy is released in the area around about 13m from working surface.Secondly,the physical model experiment of the energy evolution of the roof of the steep coal seam was builded.During the experiment,the acoustic emission signal and infrared heat change at the same time,the relevant results indicate that traits of AE parameters value compose slow evolution and rapid evolution.Heat Abnormal Zone(HAZ)emerges from the infrared thermal images and all the images could present migration phenomenon of the HAZ.The migratory phenomenon of acoustic-heat indicators is a result from inhomogeneous release of the released energy with roof-crack process.Tempo-spatial migration of the released energy is divided into slow evolution and rapid evolution,the slow change lasted for up to 40s,and the accelerated change lasted for up to 14s.Finally,the field monitoring of the energy evolution with roof-crack process of the steep coal seam was launched.During the field monitoring,the relevant results indicate that traits of the acoustic emission signal and the micro seismic signal compose slow evolution and rapid evolution.The rupture of highly concentrated phenomenon emerge from the evolution of the maximum height of the fracture,it is mainly distributed in the short distance from working face.To analyze the evolution of the energy and frequency and the maximum height of the fracture,the tempo-spatial migration of the released energy is divided into slow evolution and rapid evolution during roof-crack process in extremely steep coal seams,and the maximum energy is released in the area around about 13m from working surface,maximum energy of the daily cumulative value is 2.522 × 106J,and the roof fracturing causing instability results in dynamic hazards in the research area while the induced energy is in the rapid evolution.The research is a scientific basic and utility value on the evolution of energy with the roof-crack process of the steep coal seam,and the achievement will provide a scientific basis for site hazard prediction.