Study on Method of Enhancing Drilling Depth in Soft Outbursting Coalbeds with Roof Drilling

In order to solve the problem that borehole deformation and easy sticking when drilling in the soft outburst seam, the method of enhancing drilling depth with roof drilling was proposed. The mechanics model of roof drilling was established. The deformation, stress, and the plastic yield range around borehole after drilling were comparison analyzed by the numerical methods. The results showed that the method could effectively reduce the deformation and maximum principal stress along the top of borehole, and the plastic yield range around borehole was reduced obviously. The roof drilling process should be designed based on the thickness changes of soft outbursting coalbeds in construction sites, so as to improve the drilling depth.