Substantiation of pillar parameters in mining of inclined coal seams in Quang Ninh province, Vietnam

Design and operation of auxiliary underground workings in coal mines involves substantiation of parameters of coal pillars and requires development of new approaches to substantiate their geometrics. On the one hand, sufficient stability of a “rock mass - working - coal pillar” system should be ensured. On the other hand, the parameters of “frozen” coal reserves in the pillars should be justified. The joint solution of these two problems requires accurate forecasting based on modern digital models of a rock mass. In this study, a model of rock mass and mine workings with different dimensions of a coal pillar is presented with the use of Flac3D software. The simulation findings showed that when developing sloping coal seams, the volume of coal extraction in a longwall has an effect on the stress-strain state of the enclosing rock mass. During the study different factors having effect on geometrics of a coal pillar were analyzed, and their influence on the field of stresses and shear of inclined layers in a rock mass was studied, and the size of the plastic deformation zone around an auxiliary mine working was also determined. The study findings are also of practical importance in terms of substantiating the parameters of a working support design. The size of coal pillar is also connected with the support type. It should be taken into account that bolts should be of sufficient length to ensure firm fixing and located in the zone of intact rocks. The research showed that a coal pillar should be 10 to 15 m wide in order to ensure optimal mining conditions and safety.