| The occurrence environment,mining depth and stress level of vertical thick coal seam in Xinjiang are more complex and different than those of gently inclined coal seam.The frequent occurrence of dynamic disasters in the mining process has resulted in many casualties,which seriously threatens the safety of mine production.Surrounding rock movement characteristics and mine pressure law of vertical thick coal seam are quite different from those of near-horizontal or gently inclined coal seam.Especially,the asymmetry of"time-space-strength"caused by overburden breakage makes the law of strong mine pressure in vertical thick coal seam more complex.At present,there are few studies on safe mining and disaster control of vertical thick coal seam at home and abroad,and there is no mature technology of dynamic disaster control for reference.Therefore,it is urgent to solve the problem of power disaster control in vertical thick coal seam resources development in Xinjiang.Therefore,focusing on the difficult problem of dynamic disasters in steep inclined seam mining in southern area of Wudong Coal Mine,this paper studied the law of overburden movement and its influencing factors in steep inclined seam by means of theoretical analysis,laboratory physical simulation experiment,numerical simulation and engineering practice,analysed the mechanism of dynamic disasters,and puts forward the prevention mechanism and monitoring and early warning system of dynamic disasters in steep inclined seam.The main results are as follows:(1)The law of overlying strata migration in goaf of vertical thick coal seam was analyzed,and the characteristics of overlying strata failure were obtained.The three zones of goaf in vertical thick coal seam are large and small.There are obvious differences in weighting period and strength between different positions of working face.Overburden deformation presents the characteristics of asymmetry,persistence,abruptness and uncontrollability.The mining of vertical thick coal seam in the southern area of Wudong Coal Mine is seriously affected by tectonic stress.The pillars in the middle of the two seams are broken by successive bending.The influence of mining on the pillars is mainly concentrated at the bottom of the pillars.(2)The change characteristics of rock pillar structure during mining were studied,and the mechanism of"prying pole action"of dynamic disasters was revealed.With the increase of mining depth,the size effect of rock pillars is weakened,and the deformation form is changed from"pillar structure"to"rod structure".The pillars bend and rotate at a certain depth of unmined coal seam,which produces"prying rod effect"on coal seam.The vertical stress and shear stress at the bottom of rock pillars is concentrated.The trend of vertical displacement on both sides is opposite,and the tension stress distribution appears on the left side.The surrounding rock is mainly shear failure.The plastic zone of rock pillar extends horizontally in B3+6 coal seam mining,while the plastic zone of rock pillar extends vertically in B1+2 coal seam mining.Plastic failure zones appear on both sides of rock pillars.With the increase of mining depth,the plastic zones on both sides run through,and the stability of rock pillars decreases rapidly.(3)The main factors affecting the movement of rock pillars were studied,and the disaster-causing mechanism of the bending movement of rock pillars was revealed.With the increase of mining depth,the non-linear trend of rock pillar bending migration increases sharply,the energy accumulation in the bottom area is high,and the stress increment increases.There is a critical mining depth,which makes the activity of rock pillar increase sharply.Mining the upper coal seam first can weaken the rock pillar migration and reduce the risk of dynamic disasters.Mining activities aggravate the risk of dynamic disasters.Microseismic events in rock pillars concentrate in the 200 m range before and after the working face,and move forward continuously with the advance of the working face,and have obvious periodicity.The intensity of surrounding rock activities is related to the advance speed and daily output.(4)The coupling Weakening Mechanism of coal and rock mass based on water injection and deep hole blasting technology was proposed.Water injection further develops the internal cracks of coal and rock mass,reduces the intensity factor of the crack tip,and lays a good foundation for blasting.The detonation gas produced by blasting will pressurize the free water in the fissure twice and produce water wedge effect.It can greatly shorten the time of water injection to weaken coal body,improve the effect of permeability weakening,and form the coupling weakening mechanism of coal and rock mass.With the increase of water injection pressure,the elastic modulus and compressive strength of coal and rock mass decrease gradually,and the compressive strength of coal and rock mass decreases further after superimposed blasting weakening,and the effect of weakening increases gradually with the increase of pore size.(5)A comprehensive monitoring and early warning system of point-surface-body for dynamic disasters in steep inclined coal seams with drilling cuttings method,PASAT detection,ground sound monitoring and microseismic monitoring as its main connotation had been constructed.A comprehensive and hierarchical monitoring system of"mine regional monitoring-local key monitoring-point monitoring"had been formed to monitor dynamic phenomena of surrounding rocks with different frequencies and magnitudes and to realize comprehensive early warning.Combining with the engineering geological conditions in the southern area of Wudong coal mine,a method of multi-layer and multi-cascade combined treatment was put forward,which reduces the risk of dynamic disasters in working face by pre-pressure relief and pre-pressure relief during mining,and the effect is remarkable.The dissertation has 121 pictures,34 tables and 166 references. |
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