The Influence of a Drilled Hole on the Deformation Characteristics and Burst Proneness of Coal Samples

Abstract

Abstract Borehole drilling in a coal seam is an efficient way to relieve ground stress and prevent coal burst. The deformational behavior and failure mechanism of a Φ50mm×L100mm coal sample with a 2–4 mm diameter drilling hole were studied under standard burst proneness laboratory testing. The results show that with the increase in borehole diameter, the uniaxial compressive strength (RC), impact energy index (KE), and elastic energy index (WET) decrease, and the dynamic failure time (DT) is prolonged. The overall burst proneness of the seam changes from strong to weak for a 4 mm hole sample. A high speed camera and acoustic emission (AE) monitor were used to study the deformation procedure and failure mode of the samples. It is found that cracks are propagated around the drilled hole at the initial stage of the loading, and the AE event and energy are weakened around the peak load. This suggests that the hole may significantly reduce the brittleness of the sample. The numerical method is employed to provide further insights on the internal deformation characteristics; the effect of hole sizes with diameters of 2–10 mm is also discussed. This paper provides quantified analysis methodology, monitoring technology, and borehole optimization for pressure relief drilling and burst proneness reduction in high coal burst-prone seams.