Characteristics of loading and failure of overlying rock at working face advancing direction in longwall mining of steeply inclined seam

The effective control of surrounding rock stability is the key to safe and efficient mining in steeply inclined seam.Based on geological conditions and characteristics of strata behaviors of No.25221 working face in the 2130 coal mine,the laws of mine pressure behavior in working face and its causes are being comprehensively stipulated and researched.Then the non-uniform filling characteristics of goaf and the instability characteristics of roof strike structure at different locations in the inclination direction of working face are investigated.The study results show that the non-uniform characteristic of waste rock filling in goaf exists not only in the inclination direction but also in the advancing direction of working face,and it is easy to form an inverted triangle free face on the floor of the goaf behind the support in the middle and upper part of the working face.And the non-uniform characteristic of waste rock filling in goaf would be increased with the increase of coal seam dip angle,mining height and working face length.Under the influence of non-equilibrium constraints of waste rock,there are sig-nificant differences at the loading,deformation and failure characteristics of the roof at advancing direction as well as inclination direction between the different locations in inclination direction.Besides,because of the non-uniform filling,the migration space,frequency and amplitude of surrounding rock gradually increase,and the contribution of filling gangue to the stability of surrounding rock and the stability of surrounding rock strike structure gradually decrease from bottom to top along the inclined direction of the working face.As a result,the carrying capacity and its variation range of the support increase,and the stability of the “support surrounding rock” system gradually weakens,and it is easy to form a large incoming pressure.