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

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.

The Research on the Effect of Humidity on the Rheological Model of Swelling Rock

The research on the rheological mechanical behaviour of swelling rock in the condition of humidity field has a significant meaning for large rock engineering, such as deep coal mining, tunnelling, and slope engineering. Based on the Nishihara model, considering on the effect of humidity factor on swelling rock, the rheological elements are established and the effects of humidity on the damage of rock, the viscosity, and the elasticity are introduced. Moreover, the viscoelastic plasticity constitutive equations are established under the coupling of swelling rock stress and humidity. Afterward, considering the effects of humidity on the damage, elasticity, and viscosity, the creeping, unloading, and relaxation equations have been deduced. From this research, under the state of low stress σ3P<σS, the Nishihara model which considers the effect of humidity shows the properties of stable creeping. In addition, the unloading curves contain instantaneous elasticity, elastic after effect, and the viscosity flow induced by the humidity. However, under the state of high stress σ3P≥σS, it is an unstable creeping model. The unloading curves include instantaneous elasticity, elastic after effect, and the viscosity flow induced by the stress and the humidity. This model reflects the rheological properties of swelling rock comprehensively, and it can be used for rock rheological analysis.