Abstract: Uniaxial compression experiments were carried out on prefabricated borehole samples. Acoustic emission (AE) and digital image correlation (DIC) monitoring technology were applied to explore the mechanical response characteristics of samples arranged in multiple rows and lines, and analyze the influence of the drillhole on the bursting liability, deformation and failure, accumulation and release of energy of coal samples. The results show that, destressing drillhole in coal seam could reduce the bursting liability, control the deformation and increase the deformation energy dissipation of samples. Compared with an intact sample, the strength of the samples with drillhole was significantly attenuated, and as the number of drilling rows increased, the pre-peak elastic modulus, peak stress, and the bursting energy index KE gradually decreased, and the bursting liability was reduced. Destressing drillhole could increase the activity intensity of AE events and reduce the proportion of high-energy events. The layout of the destressing drillhole caused change of the fracture mode of the samples. A strain localization area generates from the middle on the sample surface of the intact samples, and the final fracture occurs in this area as the weak surface. For the samples with single row and multiple lines of drillhole arrangement, cracks occur on the upper and lower sides of drillholes, forming a localization zone, which extend up and down to form macroscopic cracks. For the samples with double rows and multiple lines drillhole arrangement, cracks easily occur in the rock bridge between the same row of drillholes, and then the cracks in the rock bridge between the vertical drillholes further develope, and finally form the vertical and horizontal and oblique macroscopic cracks. Morevoer, the drillhole in sample could increase the vertical drilling direction (x-direction) deformation, reduce the parallel drilling direction (y-direction) deformation, enlarge the vertical direction (z-direction) deformation, and reduce the volume deformation. The drillholes could reduce the growth UV and peak value Umax of deformation energy density, and delayed the release rate URV of deformation energy at the moment of failure. When drillhole number is greater, the reduction amplitude of the peak deformation energy density Umax and the release rate URV are greater.

Key words: drillhole pressure relief, rock burst, bursting liability, deformation characteristics, energy dissipation