Study On The Floor Movement Law Of Large Inclined And Height Working Face

The steeply dipping seam is defined by coal seam with pitch of 35°~55°.There are more than 360 billion tons of proven reserves of large dip angle coal seams in China,of which more than 60% are thick coal seams.Because of the characteristics of large dip angle and large mining height,the movement law of surrounding rock formed by mining in the working face with large dip angle and large mining height is more unique and complex.However,The coal seam floor is a damaged body formed by various geological processes.After coal seam mining,it will be affected by mechanical damage,mine pressure and other related mining movements,especially when the coal seam dip angle is greater than 35 °,it is more likely to appear the phenomenon of failure and slip.The variation of mining height is one of the main controlling factors affecting the stability of coal seam floor under the condition of large inclined coal seam.The greater the mining height,the greater the impact on the floor,and it will affect the safety of coal mining face to a greater extent.Therefore,it is necessary to thoroughly research the stress distribution characteristics and broken depth of the floor in the working face with large dip angle and large mining height.Based on the existing condition of 5# coal seam in 2130 coal mine of Xinjiang Coking Coal Group,and taking the floor of 25213 working face as the research object,physical analogous simulation,numerical simulation,theoretical analysis and engineering practice are used to systematically study the movement law of the floor in the working face with large dip angle and large mining height.The stress distribution characteristics,failure depth and slip law of the floor in 25213 working face are analyzed and studied.The main research results are as follows:(1)In the mining process of 25213 large inclined and height working face,the support pressure of floor reaches the peak value at about 5m in front of the face,and the stress release degree of floor in the upper section of working face is stronger than that in the lower section of working face.The failure of floor is dominated by tensile failure,and the maximum failuredepth occurs in the lower section of working face,and the maximum failure depth is about15 m and is in the goaf about 14 m far from the coal wall.The maximum slip of floor occurs in the middle and upper section of working face,in which the maximum horizontal slip of immediate floor is about 3m,and the maximum horizontal slip of shallow main floor is about1 m.(2)Under different mining height conditions of large inclined coal seam,with the increase of mining height,the stress reduction range of floor increases gradually.The failure depth of floor also increases with the increase of mining height.When the mining height of working face increases to 4.5m,the maximum failure depth growth of floor increases obviously,and the failure range of floor in the lower section of working face increases rapidly.The slip range of floor is also gradually extended to the deep,and the horizontal slip of floor increases gradually.(3)The stress distribution curves of floor along the trend and inclination of 25213 large inclined and height working face are given.It is pointed out that the floor is in the state of pressure relief in the working face section.The failure depth of floor increases with the increase of buried depth and mining height of coal seam.It’s preliminarily calculated that the floor is most likely to be damaged at a specific position in the upper section of goaf and at the middle position of working face along the working face’s inclination direction.(4)To the difficult problem of controlling the floor stability of 25213 large inclined and height working face,the scheme of replacing four-pillar hydraulic support with two-pillar hydraulic support and the measure of sub-regional controlling mining height,3.7m in the lower section and 4.0m in the middle section and 4.2m in the upper section,along the inclination of working face are put forward.The slip frequency of floor is effectively controlled,the overall stability of floor is obviously improved,and a good practical effect is obtained.The research results have important theoretical value and practical significance for the study on the floor failure and slip of large inclined and height working face.