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.
Highlights
A large number of randomly distributed joints and fissures make the rock mass to show properties of the discontinuity, anisotropy, and inhomogeneity
This paper mainly studies the influence of the preexisting fissure with the different filling materials on the blast-induced crack propagation and the crack propagation law at the end of preexisting fissure by experimental studies, and the crack propagation law in the experiment will be further revealed by the corresponding numerical simulation through AUTODYN. e research of this paper is conducive to improving the energy utilization efficiency of rock blasting and the effect of rock fragmentation and the safety level of fissured rock slope and tunnel, which can provide theoretical basis for improving blasting design and optimizing blasting parameters
2.3.1. e Influence of Fillings, Angle, and Distance on Crack Propagation. e mechanical properties of the fillings affect the discontinuity degree of the specimen, which was measured by the wave impedance. e wave impedances of four media are shown in Table 2 [21,22,23,24], where ρ is the density, c is the longitudinal wave velocity, η is the wave impedance, and Δη is the wave impedance difference value
Summary
A large number of randomly distributed joints and fissures make the rock mass to show properties of the discontinuity, anisotropy, and inhomogeneity. Hu et al [16] and Yang et al [17, 18] both researched blast-induced crack propagation when stress wave traveled to preexisting fissure at different incident angles in PMMA and concluded the different angles would cause the different propagation mechanism of the far-end wing crack. Many researchers have studied largely the blast-induced crack propagation law in fissured rock mass, they mostly studied the influence of single variable on crack propagation, such as stress wave incident angles [14, 16, 17] and fillings [5]. This paper mainly studies the influence of the preexisting fissure with the different filling materials (air, soil, and water) on the blast-induced crack propagation and the crack propagation law at the end of preexisting fissure by experimental studies, and the crack propagation law in the experiment will be further revealed by the corresponding numerical simulation through AUTODYN. e research of this paper is conducive to improving the energy utilization efficiency of rock blasting and the effect of rock fragmentation and the safety level of fissured rock slope and tunnel, which can provide theoretical basis for improving blasting design and optimizing blasting parameters
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