Research On Overburden Movement And Ground Pressure Behavior In Steeply Dipping And Close Distance Coal Seams Mining

When mining steeply dipping and close distance coal seam,the roof deformation,failure and movement law in lower coal seam working face are more complex,and the hidden danger in mining space is increased due to the disturbance of coal seam mining and the stability of surrounding rock structure.Taking the mining of 4#and 5#steeply dipping and close distance coal seam in Aiweiergou 2130 coal mine of Xinjiang coking coal group as the engineering background,the paper comprehensively uses the methods of physical similarity simulation experiment,numerical simulation,theoretical analysis to study the laws of roof stress state,deformation damage,roof strata caving and so on under the influence of multiple mining disturbances in the downward mining of coal seam groups.The main achievements are as follows:(1)The vertical stress distribution of roof inclination in 4#,5#coal seam mining face is asymmetric,the stress in upper and middle area is lower,the stress in lower area is higher;the roof tension stress mainly distributes in upper and middle area,and the stress release in lower area is small or no.The scope shows that the upper and middle regions are large,while the lower regions are small.With the advancing of the working face,the development trend is upward.The vertical stress distribution along the working face is symmetrical,but the stress concentration and release in the goaf of the upper coal seam have an effect on the loading and unloading of the roof of the lower coal seam.The stress concentration degree of the lower coal seam is the largest in the upper area,the second in the middle area and the smallest in the lower area.(2)There are obvious phenomena of first weighting and periodic weighting in the lower 5#coal mining face with steeply dipping and close distance coal seam.5#coal mining after 4#coal seam mining,the first weighting step of main roof is 36.3m,the average periodic weighting step of main roof is 15.2m,the average working resistance of support cycle weighting is 5943.6KN,and the average working resistance of support in usual is 3842.6kN.The influence of 4#coal seam mining on 5#coal seam mining face is that the average periodic weighting step is reduced by 25.85%,and the average load of support is reduced by 11.54%under periodic weighting.4#coal seam mining has obvious unloading effect on 5#coal seam mining.The load of roof caving strata in 4#and 5#coal seams with large dip angle and close distance is:middle>lower>upper;the load of caving strata concentrates in the middle and lower parts of downward coal seam,while the upper part does not change much.The strata pressure is strong in the central area,and the working resistance of the support is high.4#coal seam mining has obvious loading effect on the central area of 5#coal seam mining face.(3)The overlying strata of 5#coal mining face at the lower part of large dip angle and short distance coal seam form a low step structure,which is divided into first and second steps.The length of the first step rock beam is 46.1 n and the height is 5.27 m;the length of the second step structure is 58.9 m and the height is 16.6 M.Shear failure occurs at the upper end of the first step rock beam and tension failure occurs at the middle of the second step rock beam.(4)In the actual mining process of the working face 25221 in no.5 coal seam below the coal seam with large inclination and short distance,the initial pressure step distance of the basic roof is 40m,the average step distance of periodic pressure is 13 m,the working resistance of the support is 6000-7000KN.,and the loading coefficient is 1.15-1.34.The support load has obvious zoning characteristics in the inclined direction,and the working resistance of the support shows:the middle part>the lower part>the upper part.In 25221 working face,the roof pre-blasting weakening technology is used to effectively control the roof of working face and the appearance of mine pressure,so as to provide guarantee for the safe mining of working face.The conclusion of this paper has important reference value for the ground pressure control and production safety of the follow-up mining face of 4#and 5#coal seam with large dip angle in 2130 coal mine.