Investigation on coal face slabbed spalling features and reasonable control at the longwall face with super large cutting height and longwall top coal caving method

Based on the mining conditions of the longwall face with super large cutting height and longwall top coal caving (LTCC) method at the Jinjitan Coal Mine,China,this paper aimed at solving the problems caused by slabbed spalling at the longwall face with super large cutting height.The feature and mechanism of slabbed failure and spalling at the longwall face with super large cutting height were elaborated and the appropriate structural form of the face sprag and reasonable spalling control measures of coal face were studied through combining the research methods of theoretical analysis and engineering practice.It was found that the slabbed spalling has many characteristics,such as slab like spalling,onionskin like spalling,ejection type spalling and spalling caused by the disturbance of face sprags of hydraulic roof supports.Bearing capacity curves of both the integral type sprag and the split type sprag were proposed and calculated,which could also be used as an evaluation index of bearing capacity of the face sprag.The kinetic characteristics and the structural coupling relationships of the coal face and two types of structural forms of sprags were analyzed individually.It is concluded that the integral type sprag has the advantages of strong bearing capacity,excellent flexibility and high adaptability of structural coupling,which was analyzed from the perspective of mechanical properties and kinematic properties.It is suggested that the integral type sprag with two plates should be selected in priority under the premise of the required protective height of coal face is satisfied.According to the site observation,the features and damage of slabbed spalling of the coal face were investigated,and the corresponding controlling measures were put forward.The application and the maintenance effect of the split type sprag with three plates used at the adjacent longwall face with 8.2 m super large cutting height were analyzed.Combined with the structural coupling relationship between the hydraulic roof supports and surrounding rock at the longwall top coal caving face with 7.0 m super large cutting height,it is concluded that it is more suitable to adopt the integrated type sprag with two plates at the longwall top coal caving face with 7.0 m super high mining height.Production practice shows that the integral type sprag with two plates could effectively maintain the stability of the longwall coal face with super large cutting height and LTCC,and it could make contribution to automation control and high efficient mine production.