Research on characteristics of pressure arch around borehole in seambased on fluid-solid coupling dynamic model

In order to investigate the existence of pressure arch around coalbed borehole,the fluid-solid coupling dynamic model of coal containing gas based on Hoek-Brown criterion was established and solved by COMSOL software.Then,the distribution law of principal stress and the strain energy density of coal body around borehole before and after drilling in coal seams was analyzed,the variation characteristics of horizontal displacement of coal body with different structure around borehole,the inner boundary and thickness of pressure arch were studied.Furthermore,the characteristics of pressure arch was discussed combined with the distribution law of plastic zone of coal body around borehole.Research results show that pressure arch exists at the top and bottom of coalbed borehole,the arch springing and abutments locate on both sides of borehole.The changing trend of horizontal displacement of coal body around borehole in pressure arch area is relatively gentle.The inner boundary and thickness of pressure arch can be used as two indexes to evaluate the stability of coalbed borehole,and they all decrease gradually with the increase of GSI value,that is,the more complete the coal structure is and the higher the strength is ,the smaller the pressure arch range is.When GSI value is