Time effect of borehole pressure relief based on distributed optical fiber sensing technology

Based on the principle of borehole pressure relief and distributed optical fiber sensing technology,the inter- nal strain sensing model of coal around the pressure relief boreholes was established. Also,the paper proposed a meth- od of evaluating the pressure relief effect with the optical fiber tensile strain value and the radius of yielded zone. Bore- holes are drilled under the sensing cable,and the internal strain of the surrounding coal can be tested periodically. Combined with internal phenomena observation,the borehole pressure relief process can be divided into four stages,ac- cording to the characteristics of internal strain and apparent failure of coal in different times. The four stages are re- spectively fissure development stage,limit equilibrium stage,collapse hole stage,and broken coal compaction stage. The method was used to determine the time interval of each stage in the process of borehole pressure relief under the geological conditions of Xinzhouyao Coal Mine,and concluded that the pressure relief effect of construction drilling a- bove 94 to 101 m was more significant. The distribution characteristics of micro-seismic events before and after the construction time adjustment of pressure relief boreholes were analyzed by micro-seismic monitoring system. The results show that the frequency of high-energy events around the No. 8939 panel is significantly reduced,and the average en- ergy of the micro-seismic event is significantly reduced by 38% .