Research On The Stability Of Coal Wall On Large Mining Height Longwall Face In Steeply Inclined Coal Seams And Its Application

With increase of dip angle and mining height of coal seam,the ground pressure appear severe and is easy to induce coal wall spalling and roof caving in front of support in longwall working face with large mining height in steeply inclined thick seam.It leads to the difficult controlling of coal wall stability and seriously restricts safety and efficient mining in the seam.Therefore,it is great significance to study on the stability controlling of coal wall in longwall face in steeply inclined seam,which has enrich mining theory,expanded research of strata control and guided engineering practice in site.In the paper,comprehensive methods of in-situ testing,creating physical simulation model and theoretical analysis have been applied for researching on surrounding rock deformation features,characteristics of stress distribution,and coal wall stability et al.,during the mining process of longwall face with large mining height in steeply inclined thick seam.The results were as follows.In mining process of longwall face with large mining height in steeply inclined seam,the first weighting with pace of 43 meters and periodic weighting with average pace of 13 meters were appeared along strike.During the roof weighting,loads of supports were imbalance,with load of rear column larger than that of front column.Along inclination of working face,the weighting happened sequentially in different areas of working face,firstly in upper area,then in middle area and lastly in lower.The unbalanced regional feature of supports working resistance was apparent.The support working resistance in upper and lower areas was less than that in middle area of 20%,25%respectively.In upper and middle areas,the load of supports was unbalance and has large variety range,with load of head columns greater than that of end columns,resulting in elements non-integrity and instability of R-W-S-F system.The surrounding rock stress is redistributed in longwall working face with large mining height in steeply inclined thick seam,stress released area formed in roof and floor,stress concentrated area formed in T-junction.Affected by dip angle of coal seam,distribution of surrounding rock stress presents asymmetrical characteristics along inclination,with vertical stress of rib in lower area of working face larger than that in upper and middle areas.The displacement of coal wall increased linearly from up to down along inclination,with vertical displacement larger than horizontal displacement.The stability of coal wall is affected significantly by mining height and dip angles of coal seam.With increasing thickness of coal seam mining,vertical stress of coal wall transferred to front continuously,the maximum abutment pressure and its distance form coal wall increased.Horizontal displacement of coal wall reduced and vertical displacement increased,leading to probability increase of coal splling.With increasing dip angle of coal seam,the value and influence area of concentrated stress in coal wall decreased gradually with small variety range,and coal wall was easy to slipping down and a large-scale coal wall spalling formed.The coal wall spalling happened with high frequency,large range,sub-regional,spread and slip characteristics in longeall face with large mining height in steeply inclined seam.Stability of coal wall is not only influenced by coal strength,gas exceeding the limit and gas extraction,but also mainly by dip angle of coal seam,variety of mining height,working characteristics of support,periodic weighting,extraction technology,oblique angle,advancing speed of working face,hardness of roof and so on.With the increasing of dip angle of coal seam,mining height and oblique angle of working face and the decreasing of advancing speed,the possibility and frequency,influence range and degree of coal wall spalling increased.The asymmetry of abutment pressure leads to asymmetry of deformation and internal force in coal wall.The deformation of the coal wall is the largest at about 0.66 times length of working face in upper area.With increasing dip angle of coal seam,the deformation and internal force decreased in coal wall.With increasing lenght of working face along inclination,the deformation increased and internal force decreased in coal wall.Asymmetric characteristics of deformation and internal force in vertical direction of coal wall was revealed.The maximum deformation appeared at 0.6 times mining height of coal wall in upper and middle area,where the tensile stress was large and was the location of frequent instability of coal wall.Based on the controlling practice of coal wall spalling of No.25221 working face with large mining height in steeply inclined seam in the 2130 Coal Mine of Xinjiang Coking Coal Group,the comprehensive preventing and controlling technology of coal wall spalling was proposed,with controlling stability of R-W-S-F system,pre-blasting weaken of hard roof,advance strengthening of coal wall,layout of false-inclined working face with oblique angle,full-time mine pressure monitoring.The coal wall spalling and roof caving in front of support were solved effectively,safety and efficiency production of working face was achieved,beneficial technical and economic application was realized.