ZHANG Yin1,YIN Lidong1, DAI Lianpeng2, ZHANG Jiping1, LI Jiajun1, YANG Chenchen1
JOURNAL OF VIBRATION AND SHOCK. 2024, 43(9): 309-320.
Coal seam drilling is a simple, economical and effective means of impact damage reduction and mitigation. In view of the high strain rate loading after the occurrence of impact pressure, revealing the physical process of impact damage of drilled coal rock and its mitigation mechanism is of great significance for quantitatively designing the parameters of coal seam drilling. In order to study the influence of boreholes under high strain rates on the mechanical properties of coal samples, impact tests were carried out on prefabricated borehole coal samples through indoor SHPB tests and numerical simulation of particle flow. The experimental results show that borehole under high strain rate loading has a significant weakening effect on the dynamic compressive strength of coal samples, with the increase of the number of boreholes, the dynamic compressive strength of coal rock decreases by 11.9%, 20.4%, and 23.2%, respectively; and with the increase of the spacing of drilling holes, the dynamic compressive strength decreases by 20.4%, 14.9%, 8.5%, and 16.4%, respectively. The stress-strain curves of coal samples containing drill holes have a stress drop phenomenon and plastic energy consumption platform period, and the stress drop range and plastic platform range show an upward trend with the increase of the number of holes. The destruction of coal samples by borehole under high strain rate loading has obvious deformation localization guiding effect; when the coal rock is destroyed, the initial primary cracks are generated in the tensile stress area of the hole edge in the parallel loading direction, the secondary cracks are perpendicular to the direction of the primary cracks, and the inter-hole cracks are generated in the inter-hole bridges. The stress concentration zone redistributes with the breakup of the hole bridges, and the hole-side bearing zone is far away from the borehole. The peaks of AE event numbers of coal samples after drilling showed different degrees of backward shift, and the distribution of AE events was characterized by bimodal peaks when L≤2.5d, and single peaks when L>2.5d.