Mechanism And Application Of Grouting Reinforcement For Overwind Oxidation Zone In Fully Mechanized Caving Face

After the formation of coal bearing rock series,the coal rock mass undergoes deformation due to erosion and erosion by various surface stresses.Exposed to the surface and buried in shallow coal seams or surrounding rocks,they undergo varying degrees of wind oxidation under the action of water and atmosphere,forming wind oxidation zones.Their chemical,physical,and technological properties undergo a series of changes,with characteristics such as wide distribution range,developed exogenous fractures,high water content,poor permeability,and softening and swelling into mud when encountering water,directly affecting the mining and utilization of coal seams.Therefore,studying the grouting reinforcement control technology of wind oxidation zone has certain practical significance.Taking the wind oxidized rock mass of 39107 working face in Pingshuo Jinggong Third Mine as the research object,the development range of the wind oxidized zone and the physical characteristics of the coal and rock mass were analyzed using methods such as on-site investigation,indoor experiments,and borehole exploration.Conduct research on grouting reinforcement control of low permeability soft rock in the wind oxidation zone through similar simulation experiments,theoretical analysis,on-site experiments,and other methods.1)Through on-site research and experimental analysis,it can be concluded that the shallow burial depth of the coal seam is severely weathered.From the surface to the roof of the coal,the development of weathered oxidation gradually weakens,and the thickness of the weathered oxidation zone shows a trend of thin in the middle and thick in the surrounding area.The southern part of the mine field is relatively thin,while the northern part is thicker;The area with significant wind oxidation development is outside the mining range of the fully mechanized top coal caving face(northeast),while the mining range is only a local invasion,and the degree of wind oxidation development is relatively light,providing geological guarantee for safe mining of the working face.Due to the combined influence of sedimentary environment and accumulation of weathering damage,the cracks in the surrounding rock and roof of the wind oxidation zone of Working Face 39107 are developed,with loose structure and poor integrity.The weathered rock mass is severely argillated,with increased plasticity,significantly reduced self stability and bearing capacity,and is prone to local roof caving accidents.2)Based on the design experiment of visual high stress grouting test system,through the experimental results of analytical chemistry grouting material characteristics,it is found that polyurethane has the longest setting time,which can allow the slurry to fully diffuse,and its seepage radius and seepage radius length are easier to increase;The reaction product is paste foam solid,with low reaction temperature and only slight irritating gas.The mechanical properties of the consolidated body increase with time.The compressive strength gradually increases from 49.5MPa to 135.8MPa,and the tensile strength gradually increases from 3.65 MPa to 13.49 MPa.Compared with other grouting materials,the polyurethane grouting consolidated body has the largest compressive and tensile strength.Finally,Malisan was selected as the grouting material for this reinforcement project.The results of grouting experiments with different water contents show that when the water content is 6%,the diffusion distance of the slurry is about 2.96m;When the moisture content is 9%,the diffusion distance of the slurry is about 2.35m;When the moisture content is 20%,the diffusion distance of the slurry is about 2.15 m.As the water content increases,the diffusion distance of the slurry decreases,the grouting effect weakens,and ultimately only serves as a network skeleton.3)Through the analysis of indoor grouting experimental results,it was found that the diffusion forms of slurry can be divided into searching for seepage channels,manufacturing seepage channels,and pore permeability.Based on the Griffith strength theory,the formation criteria of slurry seepage channels were derived,and the radius relationship between single-phase and two-phase flow cylindrical and surface seepage diffusion was derived.It was found that the permeability radius increases with the increase of grouting pressure,permeability,and grouting time,and increases with the viscosity of slurry The increase in porosity leads to a decrease.Based on the research results,reasonable grouting parameters were selected and substituted into the singlephase surface pore permeability radius relationship equation.The calculated seepage radius was 2.55 meters,verifying the correctness of the simulated grouting experiment.Finally,the technical parameters and construction process of the wind oxidation zone grouting project were determined,and the intermittent process grouting was used to save about 66% of materials.4)The grouting effect was tested using the borehole peeping method.It was found that the borehole wall was relatively flat,and the weathered rock mass was consolidated into a whole.The original gap was filled with Malisan,and the integrity of the rock mass was improved.Through macroscopic observation of the coal wall and end face roof,it was found that during the pushing of the working face through the weathered zone,the coal wall and roof were in good condition,without any incidents of wall spalling or roof falling.The deformation of the tunnel was relatively small,and the overall integrity of the tunnel was intact,Ensuring safe and efficient mining of the working face.