Elastic-plastic analysis and shrinkage properties study of swelling rock borehole in coalmine

Abstract

The borehole shrinkage of swelling rock in coalmine is a complex problem affected by the combination of multiple fields, such as humidity field and stress field. By establishing the equilibrium equation of swelling rock borehole in coalmine, considering the expansion and softening properties, an elastic-plastic mechanics analysis was carried out, and the plastic zone radius and radial displacement of swelling rock borehole in coalmine were determined under the combination of humidity field and stress field. Taking the floor rock roadway in the 8# coal seam of Songzao Coalmine in Chongqing as an example, the influence laws of water content, ground stress, and water pressure in the hole on the borehole 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 borehole shrinkage in coalmine, and the radial displacement of borehole wall under the combination of swelling and softening is greater than that of only considering expansion or softening. With the increase of ground stress, 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 borehole, the smaller the radius of plastic zone and radial displacement of borehole wall, and properly increasing the water pressure in the borehole can effectively control the borehole shrinkage. The accuracy of theoretical analysis was further r verified by similar model tests. The results can provide a theoretical basis for solving the problem of borehole shrinkage in the swelling rock of coalmine.