Abstract Blasting-induced damage zones in rock masses are commonly identified by changes in the ratio of the P-wave velocities before and after blast. In ultrasonic tests, water is usually adopted as the coupling medium. As the ultrasonic wave propagates in the aqueous medium, the measured P-wave velocity will be affected by the water coupling distance between the transducer and the wall of the test hole. However, compared to the rock material, due to the lower dispersivity of the aqueous medium, the P-wave rise time is nearly unaffected by water coupling distance. The method based on P-wave rise time is as simple and feasible as the method based on P-wave velocity while employed in field testing. Furthermore, when P-wave rise time is used to detect blasting-induced damage zones, the measured data are in less variability and greater reliability than that acquired from the method based on P-wave velocity. As a result, while the P-wave velocity data are highly variable, the damage zone is difficult to discriminate, but it can be relatively easily discriminated using the P-wave rise time.
The aim of this study was to investigate the optimization of cut-blasting methods for deep rock masses under high in situ stress. Several plane fluid–structure interaction (FSI) models were established, and the blasting effects using common cut-blasting methods were analyzed. Considering the damage range of the rock mass and the blast-induced vibration after blasting, the cut-blasting method was selected as suitable for deep rock masses under high in situ stress. Subsequently, the cut-blasting parameters, including blasthole spacing, blasthole diameter, and the distance between the empty hole and the first cut-blasting hole, were optimized through the crack connectedness between the blastholes and the fractal dimension of the damaged rock mass. The results showed that the pentagonal cut-blasting method is more suitable for deep rock masses compared with other methods and the blasthole spacing should be reduced to resist any inhibitory effects from the increasing in situ stress. For in situ nonhydrostatic stress conditions, it is reasonable to choose a wider blasthole spacing in the direction of the major principal stress and a narrower one in the direction of the minor principal stress. Under high in situ stress, the joint optimization of blasthole spacing and blasthole diameter is recommended in order to avoid the poor cutting effect caused by too-narrow spacing. In addition, the formula for calculating the location of empty holes in shallow rock-mass blasting is also applicable to deep rock masses. The partially optimized results were preliminarily verified through comparison with existing field tests. These findings offer a new approach for enhancing the blasting effect on deep rock masses and may provide valuable guidance for the design and construction of cut blasting in deep rock masses.
The study of the shear behavior of bonded rock-cement interface is important for understanding the strength and stability of grouted rock masses. This research aims to reveal the failure mechanism behind the shear property of bonded rock-cement interfaces. For the study, sandstone and granite joint blocks with specific morphology were fabricated by using a three-dimensional (3D) engraving technique. Bonded rock-cement joints with asperity inclination angles of 15°, 30°, and 45° were prepared. Shear tests were performed on these bonded rock-cement joints to investigate the shear response and failure modes considering the effect of applied normal stress and interface morphology. Meanwhile, the two-dimensional particle flow code (PFC2D) was utilized to model the entire shear process of bonded rock-cement interfaces. The macroscopic shear behavior and mesoscopic failure mechanism were comprehensively investigated by the laboratory test and numerical simulation. The results showed that the shear stress-displacement curves of bonded rock-cement joints exhibit two distinct peaks, and the shear stress evolution can be categorized into four stages including elastic growth, rapid stress drop, secondary stress growth, and progressive softening. Significantly, the number of acoustic emission events also exhibits two distinct peaks related to the double peak of the shear stress curves. The failure of bonded rock-cement interfaces is mainly induced by shear fractures, while the failure of rock and cement blocks is primarily caused by tensile fractures. The number of shear cracks in the bonded rock-cement interfaces reaches the peak when the shear stress reaches the primary peak; whereas as the shear stress continuously approaches the residual stage, the fracture of the bonded rock-cement joints is primarily characterized by tensile cracks in the blocks.
The construction of a cut-off wall is a common reinforcement method for earth rock dams. At present, compared with the in-depth study on homogeneous earth dams, more and more attention is being paid to the stability and deformation of earth dams strengthened by a concrete cut-off wall. In this study, aiming at the Wujing project of the earth dam strengthened by cut-off wall, the influence of the water level rise and fall on the stability of the dam slope, the deformation of the dam body, and the crack width on dam crest were analyzed by numerical calculation and in situ measurement. The analysis results show that when the reservoir encounters a sudden drawdown, the safety factor of the dam slope decreases sharply. The faster the sudden drawdown, the faster the safety factor decreases. When the reservoir water level rises, the dam’s horizontal displacement shifts to the upstream direction, and the change of horizontal displacement of the downstream slope is significantly larger than that at the measuring point of the upstream slope. The water level of the reservoir rises, and the surface of the dam body rises, and the fluctuation of settlement deformation shows that the upstream side is larger than the downstream side, especially during the period of abrupt change in the reservoir water level. The longitudinal cracks on the dam crest show a tendency of shrinkage when the reservoir water level rises, and opening decreases with the decrease of deformation gradient increment and increases with the increase of gradient increment.
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