Hydraulic flushing aperture variation and anti-blocking technology considering rheological property

By analyzing the stress characteristics around boreholes,the visco-elastic plastic model of coal around hy- draulic flushing considering plastic softening and dilatancy was established,the pressure-relief and permeability im- provement effect of hydraulic flushing and aperture variation were analyzed,thus the anti-blocking technology and the measures for gas drainage improvement were formulated. The results show that:① Hydraulic punching measures can greatly improve the coal permeability around boreholes,the more punching coal amount,the greater relief range of hy- draulic flushing,the higher the permeability of coal is increased;② Shrinkage phenomenon of borehole occurs over time because of rheological properties,the greater the stress,the lower the coal strength,the more intense the creep de- formation of coal,once drainage channels are blocked,gas extraction effect will be greatly reduced;③ Anti-blocking technology by installing casting pipe reserves a drainage channel,thus high concentrations gas can be extracted for a long time,the effect of gas drainage increase by 2. 7 times;④ By gas injection combined with hydraulic flushing technique,the gas drainage amount of single hole increases by 8. 1 times, which can effectively improve gas drainage effect.