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Initiation Systems
Published in Per-Anders Persson, Roger Holmberg, Jaimin Lee, Rock Blasting and Explosives Engineering, 2018
Per-Anders Persson, Roger Holmberg, Jaimin Lee
Detonating cord is a narrow core of finely powdered PETN enclosed in a woven cover of polymer yarns and extruded plastics. Its water resistance and tensile strength can be varied through quality combinations of the yarn and the plastic cover. Usually initiated by an electric detonator, it propagates a violent detonation with a velocity of about 6500 m/s (≈ 4 miles/s) — a detonation sufficiently strong to initiate dynamite or the special primer explosives used to initiate the insensitive blasting agents, and to cause considerable damage to ANFO through which it is led.
Design of blasting patterns to induce effective caving in continuous miner depillaring panel – a case study
Published in Mining Technology, 2021
Pijush Pal Roy, Chhangte Sawmliana, Rakesh Kumar Singh
For drilling of blast holes from underground, crawler-mounted electro-hydraulic Jumbo drill machine was used as it could drill up to 30 m inclined holes at a speed of 1 m per minute. The drill rods were of 1.13 m length with connecting features (both male-female type) at both the ends and provided with a longitudinal central hole to facilitate wet-drilling. Water at the rate of 2.5 m3/hour under a pressure of 800–1000 kPa (8–10 bar) was flushed during drilling to clean the drill-cuttings out of the hole. The diameters of drill rods and drill bits were 32 and 34 mm respectively. The finished hole diameter was around 42 mm. Cartridge explosives (P1/P3 type) of 32 mm diameter and 180–200 g weight/cartridge were used. Low-grammage detonating cord containing 3.6 g of PETN/m was used for charging as well as for initiating the main explosive charge. Copper coated, instantaneous electric detonators were used for each hole to initiate the detonating cord and main explosive charges.
The influence of rock mass fracturing on splitting and contour blasts
Published in Geomechanics and Geoengineering, 2021
Marilena Cardu, Alberto Godio, Claudio Oggeri, Jacopo Seccatore
Geometric measurements were made on the bench (height, length and width), of the blasting pattern (spacing E, burden V and diameter of holes Φ) and of the amount of explosive used (kg of black power) and length (m) of detonating cord employed; in particular, two main typical cases were taken into consideration: the volume of the bench >200 m3 (7,062 cubic feet) and volume <200 m3 (7,062 cubic feet). From the analysis, lower powder factors were found out in the blasts involving larger volumes of rock, and an over-use of black powder was detected with respect to detonating cord in the benches involving lower volumes, highlighting the problem of the real need of using the black powder. Therefore, the natural fractures (pre-existing discontinuities) and those induced by the blast (excess of explosive) were evaluated, and the real displacement at the base of the bench was measured; therefore, the average displacement of the bench’s centre of gravity was calculated. The results showed that, for a given Powder Factor, the lower displacement is found where Jv is higher (Figure 14).
Effect of initiation pattern on rock damage and blasting seismic under multi-hole blasting
Published in Geomatics, Natural Hazards and Risk, 2023
Jiliang Kan, Linming Dou, Xuwei Li, Jiazhuo Li, Jinzheng Bai, Jinrong Cao, Minghong Liu
A total of five cases were designed to study the blasting seismic effect under different initiation patterns of deep-hole blasting, and the parameters of blastholes and explosives in these five cases are listed in Table 4. In Cases 1 and 2, only one blasthole was detonated and the explosives charge was 132 and 240 kg, respectively. Then, simultaneous initiation of multiple blastholes was adopted in other cases. In these cases, the explosive charge of a single hole ranges from 132 to 240 kg, and the total charge is 282, 450 and 732 kg, respectively. Moreover, the explosive used in roof deep-hole blasting is the permissible emulsion explosive for coal mines, and it was initiated by the millisecond delay electric detonator connected to detonating cord.