Abstract: It is crucial to predict the structure stability of overlying strata in steeply inclined and extra thick coal seams applying horizontal section top-coal caving (HSTCC) method. In this paper, aimed at safe miming in steeply inclined and extra thick coal seams of Urumqi mine region, the formative process and dynamical evolutionary regularity of ellipsoid-style structure of overlying strata in HSTCC condition were studied by using theoretical analysis, numerical computation and field monitoring. The results show that the non-symmetrical trend of vertical deformation is remarkable at HSTCC working face of steeply inclined and extra thick coal seam. Meanwhile, the non-symmetrical arch can be formed due to the composition of top-coal and residual overlying gangue. Sequentially the unique and steep ellipsoid-style structure will be formed dramatically. Finally, the coal-rock mass in the arch angle and apex is slided, and causes the distortion of local rock pressure, even induces dynamic hazards around working face. The results can provide guidance for the design of strata structure and height, and the prevention of dynamic hazard in steeply inclined and extra thick coal seams.

Key words: steeply inclined and extra thick coal seams, overlying strata, dynamical evolution of coal-rock, ellipsoid-style structure, instability and inducing hazard