Study On Overlying Strata Movement And Rock Pressure Behavior Of Shallow-buried And Variable Length Working Face In Baigou Mine

The output and consumption of coal in our country are increasing year by year with huge quantity,which results in the accelerated reduction of recoverable reserves of coal.In order to increase resource recovery,enterprise benefit,mining as much coal as possible,irregular working face is arranged increasing gradually.Variable length working face is one of irregular working faces with unique characteristics.This paper combines theoretical analysis,numerical simulation and field measurement with various research methods to research and analysis the law of overburden breakage,migration,stress field and displacement field variation in variable length stope.Finally,the following conclusions are drawn.1.According to the structural characteristics of roof strata,the mechanical model of roof is structured to analyze and deduce the stress and bending moment of stope roof at different stages by using the theory of elastic thin plate,and the form and shape of roof breakage are deduced.The first broken roof of short face stope is "O-X" type,and the "XO" type broken roof of transition section and long face stope is formed.The first caving step is 21.7m.Compared with the actual value,the calculated step distance of periodic fracture has a larger circumference difference,but the long face basically matches.2.Through FLAC3 D numerical simulation experiment,the evolution characteristics of stope mechanics and the law of strata movement during excavation are analyzed.The original rock stress field is destroyed by the excavation of the stope.After the stress redistribution,the front of the coal wall forms a stress increasing area,and the roof of the empty area forms a pressure relief area.In the process of advancing the working face to the interface,the increase of vertical pressure on the roof tends to be gentle.After crossing the interface and entering the long working face,the vertical stress of the roof increases obviously and the roof subsidence speed accelerates.The top plate undergoes an elastic state,a plastic state,and damage.After the joint surface,the ceiling area of the goaf increases,the amount of subsidence increases,and the speed of the overlying strata increases,which leads to the rapid development of plastic failure of the roof.3.It provides the basis for the safety production management of the working face to master the roof pressure rule through field observation.The relevant working parameters of hydraulic support are determined,the relationship between support and surrounding rock is analyzed,to evaluate the adaptability of support and roof.The first weighting step of working face roof is 20.3m and the periodic weighting step is 12.4m.The roof periodic weighting step of long face stope is 10.9m.The end resistance of support in short face stope is 44.1% of rated value,and long face stope is 51.5% of rated value.Working resistance of front and rear brackets is lower than rated.When the working face passes through the joint face,the pressure of the roof on the support increases.So the support management should be strengthened in time to maximize the effectiveness of support to achieve safe production.