Experimental study on fracture processes of granite cylinders with different decoupling conditions

Abstract

Fracture processes of granite cylinders (a diameter of 240mm and a length of 300mm) subjected to blast loading were investigated using data from three-dimensional digital image correlation (DIC) method on images captured with two high-speed cameras. The five cylinders had a centric decoupled charge (PETN) of approximately 3 g or 4 g. The centric borehole with diameter 10mm or 20mm was drilled in each cylinder, and the charge diameter was around 6 mm/7 mm. Two decoupling ratios were applied, and each specimen has a decoupled charge with water or air. A partial cylindrical surface was captured by the high-speed cameras. Both the decoupling ratio and the filled-in medium influence the fracture pattern and initiation on the surface. The specimens with the air-decoupled charge produces gas ejection 440 μs-460 μs after detonation, while the specimen with the water-decoupled charge presents gas ejection at 960 μs. Displacement fields determined from the 3D DIC analysis were used to obtain strain fields on the observed surface. It is found that the initial strain on the surface was seen approximately 40 μs after the detonator initiation. The air-filled gap yields the vertical strain concentration zone in priority, while the water-filled gap produces horizontal concentration zone. The strain concentration corresponded well with the locations and direction of the developed cracks. The experimental findings of this investigation indicate that the decoupling ratio and decoupled materials have a great impact on rock fracturing.