Research on testing technology of deformation and failure of boreholes in coal seam gas drainage and its application

In order to reveal the instability and failure rules of coal seam gas drainage and the characteristics of its service life cycle,the drilling deformation and fai lure testing system that includes the drilling deformation simulation device and the drilling deformation testing device was developed,and the whole process of borehole deformation and failure was tested by using similar materials. The relationship between the pressure of the pressure sensor and the borehole deformation was studied, and the index of borehole damage degree is proposed to evaluate the deformation and failure state of boreholes. Based on the test data,the qualitative relationship bet ween the borehole failure degree and the pressure of the pressure sensor was established. According to the test results,the borehole collapse was determined to be gre ater than 50%. The deformation and failure process of gas drainage boreholes was tested on site,and the variation law of borehole damage degree with time and boreh ole depth was analyzed,and the borehole stability was quantitatively investigated. It was found that the initial deformation failure rate was fast and the degree was larg e,and then entered the stage of slow deformation and failure until it stabilized;along the direction of borehole depth,the damage degree of borehole first increased and t hen decreased,the damage degree of borehole was the largest in the range of 5 ~ 11 m,which was consistent with the stress distribution of surrounding rock around th e roadway,and it was of guiding significance for determining the reasonable sealing depth. The deformation and failure of the borehole has a significant impact on the g as drainage flow. As the damage of the borehole increases to 50% and above,the borehole fails,and the gas drainage cannot be continued. The research results provid e a basis for reasonable gas drainage design,gas drainage dynamic investigation and accurate evaluation of drainage effect.