A new effective method and new materials for high sealing performance of cross-measure CMM drainage boreholes

This study focuses on improving the sealing performance of the cross-measure CMM (coal mine methane) drainage boreholes. The sealing of cross-measure CMM drainage boreholes is not only related to the gas emissions but also closely related to the CMM drainage efficiency and further affects the safety of the coal miners. However, the sealing performance of the traditional sealing method becomes increasingly poor with increasing mining depth. The three main shortcomings of the traditional sealing method were revealed based on the examination of the geomechanical factors and characteristics of the traditional sealing materials. To eliminate these shortcomings and obtain an effective sealing method, 10 groups of sealing materials were tested; an automatic grout pump and two types of rubber bottom subs were developed. Next, a new sealing method, which is characterized by performing grouting two or more times with high grouting pressure was developed and compared with the traditional sealing method in engineering. The cement grout with a cement-to-water ratio of 1:0.8 is a suitable sealing material from both engineering applicability and economic perspectives. The new sealing method has a better sealing performance of the cross-measure CMM drainage boreholes than that of the traditional sealing method based on the engineering test results.