The Influence Of Humidity Field On Swelling Rock Boreholes Deformation In Coal Mines

Pre-pumping coal seam gas are one of the main measures to control coal mine gasaccident. When drilling holes for gas pre-extraction, especially cross expansivemudstone, mudstone in hole will quickly expand when encountering water and causedborehole accidents such as pipe-holding. So, the drilling efficiency and coal mine safetywill be largely affected. Therefore, it is necessary to investigate the boreholes’deformation law under the humidity field, which could help deducing accidents toprevent gas disasters in coal mine.Aimed at the problem of boreholes shrinkage crossing swelling rock in coal mine,in this paper， based on the humidity stress field and thermo elasticitytheories,deformation rule of coalmine swelling rock boreholes under different water contentwere systematically studied and analyzed by the software ANSYS and similar modelexperiment.The main conclusions are stated as follows:①The mechanical properties of mudstone in a coal mine in Chongqing werestudied by uniaxial compression and expansion experiment. With the water ratioincreasing, elastic modulus and compressive strength of mudstone are decreasing，inaddition to mudstone has a strong swelling. Therefore, in the theoretical analysis andpractical engineering applications, considering the soften and expansion characteristicsof swelling rock is essential.②Based on the humidity stress field theory and thermoelasticity,in this paper,considering the humidity softening effect of swelling rock constitutive model, and mineexpansion drilling diameter rock deformation is analyzed theoretically, for a givendrilling, radial displacement component of the cell wall of the main changes with themaximum moisture content provide a theoretical basis for the numerical simulation ofthe next step.③The effects of the humidity field on boreholes shrinkage were systematicallystudied and analyzed by the software ANSYS and similar model experiment. Underconstant stress field and different humidity field, the relation between the radialdisplacement of borehole wall and water rate was non-linear increasing;under constantstress and moisture field, the maximum radial displacement of the borehole wallincreases with wet line expansion coefficient increasing, the Poisson’s ratio, the elasticmodulus increases with the decrease. It can be seen that when drilling through the broken swelling rock zone with fissures, radial displacement of borehole wallsignificantly larger, more significant amount of necking, so when drilling conditions arepoor swelling rock formations, it should be noted prevent drilling necking sticking.