Study On The Mechanism And Control Technology Of Rib Spalling In Fully Mechanized Top Coal Caving Mining With Steep Dipping And Thick Coal Seam In Beixinyao Mine

A large number of steeply dipping coal seams in China are difficult to be mined efficiently due to the limitation of mining conditions and mining technology.Beixinyao Coal Mine is a large mine built by Datong Coal Mine Group in Shuonan.Its coal seam has the characteristics of large dip angle(21-37°),thick coal seams(4.3-7.0m).The 110203 working face,as the first mining face of the mine,encountered serious rib spalling problems.Due to the lack of relevant research and experience,the mine production was slow.Therefore,this thesis takes the 110203 working face as a engineering background,a combination of experiments,field measurements,theoretical analysis,numerical simulation,and engineering application methods were used to test the coal-rock mechanical parameters testing and analyze the rib spalling characteristics in the field,study the relationship between the position of rib spalling and the mining height and inclination angle,reveal the mechanism of rib spalling in steeply Dipping thick coal seam fully mechanized caving mining,and propose the rib spalling control technology for steeply Dipping thick coal seam fully mechanized caving mining.The research showed that:(1)The uniaxial compressive strength of the 2# coal seam mined by the 110203 working face was 9.33 MPa,tensile strength was 0.87 MPa,cohesion was 1.18 MPa,internal friction angle was 27.5°,and the f was less than 1,indicating that it was a weak coal seam,which is prone to rib spalling during the fully mechanized caving mining of the top coal in steeply Dipping coal seam.(2)A mechanical model of rib spalling was established,and it was found that the critical force for rib spalling was related to the mining height h and the coal stiffness(EI).The larger the mining height,the smaller the critical force for rib spalling,and the easier the rib would spall.The greater the bending stiffness of the coal wall,the greater the critical force for rib spalling,and the less likely the rib would spall.When the mining height was 3m and the inclination angle was 22°,rib spalling was prone to occur at a position 0.3m away from the coal seam roof.(3)The force formed by the roof above the coal wall of the steeply inclined coal seam is more likely to decompose,causing stress concentration in the coal wall and in front,which is easy to cause deformation and failure of the coal wall.As the inclination angle and mining height of the working face increased,the horizontal displacement of the rib increased continuously,the failure mode of the coal wall in front of the face changed from shear failure to tensile failure,and the plastic zone increased.With the increase of the internal friction angle and cohesion of the coal,the horizontal displacement and plastic zone of the rib gradually decreased,and the depth of the rib failure decreased.(4)It was determined that the mining height of the 110203 working face was 3m,the step distance for caving was one cut and one caving,and the initial support force of the support was 24 MPa,which ensured the mining efficiency of the fully mechanized caving working face while ensuring the stability of the rib.A grouting scheme for the rib was proposed: the grouting hole depth was 5.5m,the hole spacing was 3m,the hole diameter was 42 mm,the drill holes were arranged in a three-flower pattern,and high-water-rapid-setting grouting material was used for grouting.The grouting pressure range is 3.0 ～ 4.0MPa.(5)During the period of normal mining and the pressure period of the 110203 working face,the rib spalling mainly occurred in the upper and waist parts of the coal wall.After grouting reinforcement,the depth of rib spalling in the upper,waist and lower parts decreased to the range of 170-380 mm,120-360 mm and 80-120 mm respectively.Compared with the depth of rib spalling before grouting,the average depth of rib spalling at different positions decreased by 41%,37.5%,20% and 38.5%respectively.(6)The application of coal wall rib spalling control technology engineering has shown that the monthly output of the working face has increased from 195,600 tons to258,000 tons,with an increase of 62,400 tons per month,improving the mining efficiency by 31.9% and bringing huge economic benefits.The thesis has a total of 46 figures,10 tables,and 69 references.