Elastic-plastic analysis and shrinkage properties study of swelling rock boreholes in coalmines

The shrinkage of swelling rock boreholes in coalmines is a complex problem affected by multiple fields coupling, such as humidity field and stress field. By establishing the equilibrium equation of swelling rock boreholes in coalmines, considering the expansion and softening properties, the elastic-plastic mechanics analysis was carried out, and the plastic zone radius and radial displacement of the surrounding rock of the swelling rock in coalmines were determined under the coupling of humidity and stress field. According to an example based on the research background of the floor rock roadway in the 8# coal seam of Songzao Coal Mine in Chongqing, the calculation results were carried out, and the influences of water content, ground stress and water pressure inside the hole on boreholes shrinkage were studied. The results show that with the increase of water content  of the surrounding rock, the radius of plastic zone and radial displacement of borehole wall gradually increase; Both the humidity expansion and softening have an important influence on boreholes shrinkage in coalmines, and the radial displacement of borehole wall under the coupling of swelling and softening is greater than that of only considering expansion or softening; With the increase of the ground stress P, the radius of plastic zone and radial displacement of borehole wall gradually increase, showing a nonlinear increasing relation; The larger the water pressure in the boreholes, the smaller the radius of plastic zone and radial displacement of borehole walls, and properly increasing the water pressure in the boreholes can effectively control the boreholes shrinkage. The accuracy of theoretical analysis was further verified by indoor model tests. The results can provide a theoretical basis for solving the problem of boreholes shrinkage.