Effect of the Preexisting Fissure with Different Fillings in PMMA on Blast‐Induced Crack Propagation

Abstract

In order to study the dynamic crack propagation law in fissured rock under the different fillings, a borehole with 7 mm diameter was processed in the center of a polymethyl methacrylate (PMMA) specimen. The preexisting fissure with different angles (θ = 0°, 45°, and 90°) and different distances (L = 20, 30, 40, 50, and 60 mm) was prefabricated around the borehole. Air, soil, and water were employed as fillings in the fissure, respectively. The experiment of explosive loading was carried out by a single detonator, and the dynamic crack propagation process of the experimental specimens was simulated by nonlinear dynamics software AUTODYN. The results show that the blast-induced cracks are the most favorable and unfavorable to propagate when θ = 0° and θ = 45°, respectively. The length of the far-end wing crack decreases with the increase of the distance L, and the length of the far-end wing crack in the air-filled specimens is larger than those in soil-filled and water-filled specimens. The damage-pressure curve of the far-end wing crack initiation point shows “S”-type change, and the damage-pressure curve shows two obvious damage evolution processes of initial nonlinear and later linear stages. With the increase of the angle, the distance from the borehole to the crack initiation point decreases and the compressive stress wave peak value should increase, but the tensile force peak value decreases. Meanwhile, the relationships between pressure and average velocity of the initiation point and L, θ, and fillings are established, respectively. The numerical simulation agrees with the experimental results well. It can be seen that the fillings types, angle, and distance have a mutual restraint relationship with the reflected and absorbed stress wave energy. The phenomenon of crack propagation under different fillings can be explained well from the viewpoint of discontinuity degree and stress wave energy, which reveals the general law of blast-induced crack propagation.

Integrated geophysical methods for boulder delineation to improve mining

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Study on the Combined Effect of Inclined Natural Fracture and Water Jet Slot on the Blast-Induced Crack Propagation Law

“…As the incident angle is greater than 75 °, new developed cracks are very small. Yang et al [35,36] studied the influence of artificial cracks with different positions, different orientations, and different filling materials (water, air, clay) on the propagation of single ordinary blast hole explosion-induced crack, and the results show that blasting cracks almost cannot surmount prefabricated fissures, and total cracks and left and wing cracks of models with filling air almost are larger than the models with filling clay and water. By using a dynamic caustic line test system, Yue et al [37][38][39][40] studied the propagation process of stress wave, crack propagation mechanism, and multiple joint fissure penetration mechanism in defective medium under explosion load.…”