Research On Stress Response Characteristics And Slagging Law Of Bedding Borehole In Soft Coal Seam

In recent years,coal mine gas(coalbed methane)has attracted attention from all walks of life as a clean,high-efficiency,high-quality energy.Strengthening coal mine gas drainage is an effective way to control coal mine gas power disasters and develop new clean energy.More than half of the mines in my country are high gas outburst mines,and more than 95% of the coal seams mined in high gas mines are soft coal seams.Due to the small solidity coefficient and low mechanical strength of the soft coal,the coal seam gas drainage drilling has a large slag output and poor stability,which greatly reduces the pore depth and porosity rate of the gas drainage drilling,and seriously affects the coal seam.Gas drainage scope and drainage effect.This paper takes the bedding drilling in soft coal seam as the research object,and adopts the research method of theoretical analysis,drilling simulation test and numerical simulation test to analyze the hole circumference under different conditions of compressive strength,ground stress,and drill diameter.To carry out theoretical and experimental research on the characteristics of stress response,the law of borehole deformation and displacement,and the characteristics of borehole slag generation.According to the similar simulation theory,the standard specimens of cylinders with different mass ratios were produced.Through uniaxial compression failure test,the compressive strength changes of the cylinder standard specimens with different mass ratios were analyzed,and it was found that the ratio of water to paste was At a certain time,the uniaxial compressive strength of the specimen decreases with the increase of the sand-to-rubber ratio;when the sand-to-rubber ratio is constant,the uniaxial compressive strength of the specimen is positively correlated with the water-gypsum ratio.According to the relevant specifications,the compressive strength of the cubic specimen with the diameter of the cylinder standard specimen as the side length is calculated,and according to the characteristics of the soft coal seam,the compressive strength of the cubic specimen is preferably corresponding to 1.3 MPa,1.8 MPa,and 2.6 MPa.The mass ratio scheme of the standard specimens of the cylinder is used as the scheme of the specimens used in the simulation test of drilling and drilling along the bed in the soft coal seam.Based on the borehole stress and strain theory and the simulation test of drilling along the bed in the soft coal seam,the mechanical response mechanism and the slag generation law of the drilling instability of the soft coal seam are analyzed.The test adopts a self-developed true three-axis servo loading control system and a simulated drilling rig test system.The strain bricks are pre-embedded in different positions inside similar specimens,and the stress response characteristics around the borehole during the test are monitored,and the endoscope is used to Penetrate the deformation and failure characteristics of the borehole wall.The results show that low compressive strength and high ground stress will cause deformation and instability of the borehole;the ground stress on the specimen has the greatest influence on the peak value and position of the vertical stress around the borehole and the amount of slag produced by the borehole.The increase in ground stress increases the peak vertical stress around the drill hole by about4.39 MPa,and the distance from the center of the drill hole by about 6.22 mm.The ratio of the influence of the change in ground stress on the slag production per unit depth of the drill hole is as high as 1.34 times.The compressive strength of the specimen has the second effect on the peak value and position of the vertical stress around the hole,the deformation and failure of the borehole,and the amount of slag produced by the borehole.With the increase of the compressive strength of the specimen,the peak value of the vertical stress around the borehole increases by about 1.43 MPa,and The distance between the center of the borehole is reduced by about 2.74 mm,and the impact of the change in compressive strength on the amount of slag produced per unit depth of the borehole can reach 1.27 times.However,the change of drill diameter has no significant effect on the peak value and position of vertical stress around the hole,and the amount of slag produced by the hole.In addition,through comparative analysis of actual drilling slag production data in soft coal seam mines,corresponding engineering verification of the test law was carried out.Based on the effective stress principle of the gas-containing coal,the ABAQUS numerical simulation software is used to conduct numerical test analysis on the stress distribution and hole wall displacement of the gas-containing coal under different conditions.The results show that the vertical stress peak value and position of the coal body around the drill hole,and the displacement and deformation of the hole wall all change with the changes of the coal body's compressive strength,ground stress,and gas pressure.When the in-situ stress on the coal body is 25 MPa,the maximum vertical stress in the coal body around the hole is 35.11 MPa,and the displacement and deformation of the hole wall is 17.16 mm.When the compressive strength is 2.6MPa,the maximum vertical stress of the coal body around the hole is the farthest from the center of the borehole,and the displacement and deformation of the hole wall are the largest,respectively 116 mm and 17.31mm;when the compressive strength increases to 5.2MPa,the hole circumference The vertical stress peak of the coal body is 65 mm from the center of the borehole,and the displacement and deformation of the hole wall is 5.19 mm.The change of the drill diameter will not cause a large change,and the change of the drill diameter has little effect on the stability of the borehole.The numerical simulation results are in good agreement with the physical test results.