Strain Field Development, Fracturing, and Gas Ejection in Decoupled Charge Blasting Using Granite Cylinders.

This study explored the fracture process of granite cylinders with a centric charge, varying decoupling ratios by conducting laboratory-scale experiments and numerical simulations. In experiments, the three-dimensional (3D) digital image correlation (DIC) technique was employed, using frames captured by two synchronized high-speed cameras. This instrumentation permitted the observation of full-field strain variation, the development of fractures, and gaseous products escaping from the cylinders' surfaces. Granite cylinders measuring 240 mm in diameter and 300 mm in length served as specimens in blasting experiments, and each specimen had a charge of approximately 3 g. Specimens had a centric blasthole with a diameter of either 10 mm, 14 mm, or 20 mm. The corresponding decoupling ratio varied from 1.8 to 3.6, and the gap between the charge and the blasthole wall was filled with water or air. The experimental results showed that: (1) specimens with decoupling ratios of 1.9 and 2.6 exhibited initial strains on the cylindrical surface between 20 μs and 40 μs. (2) Specimens with water-filled blastholes developed fractures faster and in a denser manner compared to those with air-filled blastholes. In addition, fractures resulting from air-filled blastholes appeared smoother than those from water-filled blastholes. (3) The gas ejection time for the air-filled blasthole remained basically consistent across decoupling ratios ranging from 1.5 to 3.61, varying between 400 μs and 520 μs. The utilization of water-filled blastholes effectively minimized the escape of gaseous products from the cylindrical surface. Numerical simulation conducted with LS-DYNA exhibited results that aligned well with the observed fracture patterns in the experiments. This study aims to provide a better understanding of the fundamental mechanisms of rock behaviors in decoupled charge blasting. Highlights: Decoupled charge blasts were conducted on granite cylinders (⌀240mm×300mm) using the digital image correlation analysis and high-speed cameras. For specimens with decoupling ratios of 1.9 and 2.6, initial strains on the cylindrical surface were observed between 20-40 μs. Water-filled blasthole specimens developed fractures faster and denser compared to air-filled blasthole specimens. The decoupling ratio of 1.5-3.61 in air-filled blasthole specimens barely influenced gas ejection time, which varied from 400 μs to 520 μs. [ABSTRACT FROM AUTHOR]