By analyzing the vibration signals of three different decoupling decked charges measured in a mine, the vibration effects is discussed by Fourier analysis and wavelet (packet) analysis. From the time-frequency analysis, it is found that the vibration effect of three charge structures is different. The vibration effect decked with rock powder is the most intensive; while that with water is inferior, and that with air is the minimum. As a result, the method decked with water or air is of benefit to the improvement of blast quality and the protection of slope.

Keywords: decoupling decked charge; blasting vibration effect; time-frequency analysis

Model experiments using PMMA plates and electric detonators were carried out to observe the dynamic fracture process between two charge holes in blasting by means of high-speed videography. The experiments are related with control of fracture planes along the line connecting the charge holes in smooth blasting. In this paper, firstly, the influence of the initiation time lag on the fracture formation between two charge holes was discussed. Secondary, the effect of a guide hole on fracture control was examined. The experimental results showed that the effect of stress reinforcement exists by simultaneously firing two charges. Applicability of the guide hole method using the circular hole having two notches for fracture plane control between two charge holes was demonstrated. The fracture process near the guide hole with two notches was also analyzed by numerical calculations using the dynamic finite element method.

This contribution addresses size and boundary effects on wave propagation, fracture pattern development and fragmentation in small scale lab size specimen for model blasting. Small cylindrical specimens are center-line loaded by linear explosive charges and supersonically detonated. Using elastic wave propagation theory and fracture mechanics it is shown that the type of boundary conditions which prevail at the outer boundary of the cylinder control the extension of borehole cracking and fragmentation within the body of the cylinder. In the case of a composite cylinder where the core is of a different material than the mantel, the level of fracturing and fragmentation is controlled by the separation of the interface which in turn depends on the relative diameters of the core and the mantel. The most important parameter though is the ratio between the length of the pulse (space-wise or time-wise) and the characteristic dimensions of the models, i.e. in this case the diameters of the core and the mantel. The plate like specimens is either a single cylinder or consists of a possibly dissimilar core and a mantel. The core is always a cylinder but the mantel can be either a cylindrical or square tube. In all cases the blast-hole and explosive is in the center of the specimen.

Assuming that the vibration waves emitted by successive detonations in the near by holes, each having an identical set of explosives, are identical each other, a proper delay between holes, which significantly reduces the peak particle velocity (PPV) at any point of interest, can be designed, based on the theory of superposition of waves. Blast vibrations were measured in situ in order to design an efficient production blasting in an open pit limestone quarry, where the pit floor is approaching an abandoned stope whose roof must be maintained stable to prevent the pit floor from caving in. A relationship between PPV at the measuring point and the distance to epicenter was considered. Also PPVs based on different criteria, i.e. PPV minimization and auto-correlation minimization, were compared. Finally, two dimensional FEM analysis, based on the data of the in situ blast vibration measurements, was performed to estimate the distribution of the PPVs around a particular target point.

The energy partitioning of limestone production blasts has been measured under well controlled conditions; from rock properties determination, structural mapping and monitoring of drilling and charging, to VOD, 3D accelerometer and bench face movement measurements during the blast to post-blast fragment size measurements. The efficiency of the transfer of energy from the charges to the surrounding rock has been estimated by introducing a new explosives test, the cylinder expansion test, which is discussed to be-gin with.
Hereby in-hole losses, seismic energy, kinetic energy of throw and fragmentation energy have been calculated. For the AN doped gassed bulk emulsion used in the quarry, it is estimated that 60-70 % of the explosive energy is transmitted to the rock, that the seismic and kinetic energy terms both amount to roughly 3-12 % and the fragmentation energy to less than 1-2 %. One candidate for the remaining losses, which are larger than the other three terms together, is the crushing of the blast-hole region. A rough estimate for the energy partitioning in bench blasting rounds is finally given.

Rock blasting has two sides of technical skill. In terms of rock blasting, the optimum result is one that maximizes production and minimizes the damage to the remaining rock. To control fragmentation the proper amount of energy must be applied at appropriate sites taking into account rock mass characteristics. On the other hand, the remaining rock mass itself is required to remain stable as a part of a structure. A special type of blasting technique must be used which minimizes the damage done in the remaining rock. This paper presents two case studies of solving problems for control of fragmentation and damage to the rock mass.