Deformation characteristics of gas drainage borehole in loading and unloading

The stability of gas drainage borehole affects the quality of extraction engineering. In the process of mining,the abutment moves along with the advance of the working face,and loading and unloading stresses act on the borehole in mining influence area. In order to obtain the deformation and failure law of the borehole under the condition of loading- unloading,the authors used a numerical method to calculate the failure of boreholes at different stress change rates. Based on ten calculation schemes,the drilling plastic zone distribution and the hole wall displacement curve under differ- ent loading and unloading stress changing rates were obtained. At the same time,according to the relationship between the rate of unloading stress and the deformation of the hole wall was obtained by numerical calculation. The calculation model of shear stress around the borehole was established,which considered the rate of unloading stress change. Research indicates that the loading process,loading rate do not affect the extent of damage surrounding borehole and hole wall dis- placement. The unloading process around borehole damage range is associated with the initial unloading stress and unloa- ding rate. In the drilling arrangement the stress characteristics of boreholes should be considered.