The role of empty hole in rock blasting is getting more and more attention.In order to study the influences of empty holes and their defects on the cracks propagation in rock blasting, PMMA was used to replace rock materials, and a dynamic caustics system was used to mainly study the influences of empty holes and their defects at the back-blast side on the cracks propagation.Under the conditions of the same pre-crack length and the same distance from the blasthole, when the hole diameter is 10 mm, 20 mm and 30 mm, the crack length is 1.46 cm, 2.13 cm and 5.29 cm, the crack propagation speed is 266.64 m/s ,366.63 m/s and 466.64 m/s, and the stress intensity factor is 0.89, 1.11 and 1.34, respectively, it is found by the experiments that as the diameter of the empty hole increases, the pre-crack propagation at the back-blast side is easier.The mechanism was explained by establishing a mechanical model.The increase of the diameter of the empty hole enlarges the reflection range of the stress wave, and enhances the intensity of the forces acting on the rock mass unit at the boundary of the empty hole, which leads to the generation and development of cracks.Under a certain range of hole diameters, the direction of the resultant force generated by the reflected stress wave of the empty hole affects the crack propagation at the back-blast side, which is mainly manifested in the relationship between the directions of the horizontal force component of reflective stress wave and the crack propagation.When the two directions are the same, the crack propagation is promoted propagated crack length is longer, when the two directions are opposite, the crack propagation is suppressed with shorter propagated crack length.
Key words
rock blasting /
empty hole /
pre-crack /
crack propagation
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References
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