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Rock Blasting And Explosives Engineering.pdf

Rock Blasting and Explosives Engineering covers the practical engineering aspects of many different kinds of rock blasting. It includes a thorough analysis of the cost of the entire process of tunneling by drilling and blasting in comparison with full-face boring. Also covered are the fundamental sciences of rock mass and material strength, the thermal decomposition, burning, shock initiation, and detonation behavior of commercial and military explosives, and systems for charging explosives into drillholes. Functional descriptions of all current detonators and initiation systems are provided. The book includes chapters on flyrock, toxic fumes, the safety of explosives, and even explosives applied in metal working as a fine art. Fundamental in its approach, the text is based on the practical industrial experience of its authors. It is supported by an abundance of tables, diagrams, and figures. This combined textbook and handbook provides students, practitioners, and researchers in mining, mechanical, building construction, geological, and petroleum engineering with a source from which to gain a thorough understanding of the constructive use of explosives.

Rock Blasting And Explosives Engineering.pdf

Small-scale model blasting plays an important role in understanding mechanism of rock fragmentation by blasting and improving blast technology in rock and mining engineering. Because a specimen (or model) often needs to be placed on either a ground or another material in model blasting, an additional interface appears between the specimen and the ground (or material), compared with an engineering blast that does not have such an interface. In this paper, four model blasts with high-speed photography were presented. The results showed that: (1) as the impedance of a rock specimen was smaller than that of the ground material, the specimen was thrown up and a certain amount of kinetic energy was brought with such a bounce. Thus, this placement should be avoided in model blasts. (2) As a rock specimen was placed on three blocks of the same type of rock as the specimen the specimen was not bounced up during blasting. Correspondingly, no kinetic energy was induced by specimen bounce. Therefore, this placement is recommended for model blasting. If very high specific charge must be used in model blasting, the above-recommended method will not work well due to possible breakage of the base material during blasting. In this case, the rock specimen can be placed on a material with smaller impedance than that of the rock specimen so that specimen bounce can be reduced. Accordingly, such a possible specimen bounce should be estimated by stress wave analysis.

A good solid explosive can convert energy at a rate of 1010 watts per square centimeter of its detonation front (Fickett and Davis 2000). Upon detonation, an explosive can produce a pressure over 20 GPa and a temperature above 3000 C. Explosives are so powerful that rock blasting has been used in hard rock mining and hard rock engineering for over one century. However, up till now rock blasting has been dominated by empirical design, resulting in considerable mineral loss, poor safety, high vibrations, explosive wastage, and induced seismic events (Zhang 2016). One of the main reasons for the empirical design is that the mechanism of rock fragmentation by blasting has not been well-understood so far. To make a blast design more scientific and a blast operation more economic, more efficient, and less environment-disturbed, it is necessary to carry out various model blasts.

A great number of model blasts have been carried out for several decades (e.g., Field and Ladegaard-Pedersen 1971; Bergman et al. 1973; Fourney et al. 1974, 1981, 1993, 2006; Dally et al. 1975; Bhandari 1979; Rustan 1995; Nie et al. 2000; Nie and Olsson 2001; Moser and Grasedieck 2004; Katsabanis et al. 2006, 2014; Tilert et al. 2007; Johansson and Ouchterlony 2013; Onederra et al. 2013; Sun 2013; Fourney 2015; Liu et al. 2018; He et al. 2018; Chi et al. 2019a, b, c; Yang et al. 2019; Zhang et al. 2020a, b, 2021; Mao et al. 2020). In various model blasts including those mentioned above, the constraint condition to a blasting specimen is usually different from that in engineering blasting, giving rise to that the results of a model blast are different from the ones of an engineering blast to a certain extent. The first discrepancy between an ordinary model blast and an engineering one is that there are often more free surfaces in the model blast than in the engineering blast. To minimize the effect of multiple free surfaces on the result in model blasts, mortar models were employed in which an ordinary rock-like specimen was tightly enclosed by a larger volume of mortar material (e.g., Johansson and Ouchterlony 2013; Sun 2013; Katsabanis et al. 2014). In this way, the stress wave reflection from the interfaces between the rock-like specimen and the larger volume of mortar can be avoided if the characteristic impedances of the specimen and the larger mortar are matched each other, even though the wave reflection from the free surfaces of the larger mortar still exists.

Besides the first discrepancy, the second one between a model blast and an engineering blast is that there is an interface between the rock (or rock-like) specimen and the ground (or another object) on which the specimen is placed in the model blast, but such an interface does not exist in the engineering blast. Compared with the engineering blast lacking such an interface, the interface in the model blast will cause stress wave reflection (unless the impedances of both the specimen and the ground are equal to each other). Correspondingly, a certain amount of explosion energy will be carried by the reflected wave, and additional movement of the specimen will be induced. As a result, fracture and fragmentation in the model blast might be affected more or less, depending on the conditions of the interface, i.e. the placement of the specimen. Unfortunately, the effect of specimen placement on blasting results in model blasting has not been investigated up till now. Accordingly, this paper is to demonstrate that a rock specimen can be thrown up during blasting if the placement of the specimen is not correct. Then, simple stress wave theory is used to analyze the movement of a blast model placed on a floor with two different material impedances. Finally, proper or correct methods for placing rock specimens in model blasting are suggested.

This case includes two specimens S3 and S4. S3 was a cylindrical granite specimen and S4 a cubic granite. During blasting either S3 or S4 was placed on three rock blocks that were piled on the floor of the explosion chamber, as shown in Fig. 1b, c. There was no confinement to the specimens. The blocks and the rock specimens were manufactured from the same type of granite in the quarry. The sizes and other parameters of S3 are indicated in Fig. 1 and Table 1.

Similar to S3, S4 was placed on three rock blocks during blasting. Its sizes and other parameters are indicated in Fig. 1 and Table 1. The selected high-speed photographs are shown in Fig. 5. Obviously, the vertical movement of S4 is nearly zero at all pictures including last one at time 13.3 ms. Note that the picture at 798 µs after the initiation of detonation shows the main cracks have already been visible.

Moreover, notice that many rocks are composed of one crystal or multiple crystals (such as calcite and quarts). The measured surface energy of calcite was 0.35 J/m2 (Santhanam and Gupta 1968) and that of quarts varied from 0.41 to 1.03 J/m2 under room temperature and dry condition (Brace and Walsh 1962). Assume that average surface energy of the crystals in various rocks is 1 J/m2, we can find that 326 J energy may create 326 m2 new surface area in rocks. Evidently, this amount of energy cannot be neglected in model blasting.

Model blasting is carried out mostly in a blast chamber, but sometimes outside of a laboratory room such as an open field. In most cases, blast models, either rock or rock-like materials such as concrete and cement, are placed on the ground of the blast chamber, as shown in Fig. 1a. The models are either cylindrical or cubic and they often have free surfaces in lateral sides. In order to simplify the analysis, it is assumed that (1) the explosive charge is concentrated at the center of the model and the length of the P-waves caused by blasting in the model is short, (2) such P-waves in the model are approximately elastic compressive waves, and (3) the S-waves and Rayleigh waves either caused by blasting or induced by an inclined incidence of P-waves on a free surface are neglected. According to one-dimensional stress wave theory (Kolsky 1963; Johnson 1972; Wang 2007; Zhang 2016), as one elastic wave propagates from one material, defined as the first material, with stress \(\sigma _I\), particle velocity \(v_I\), density \(\rho _1\) and wave velocity \(c_1\) to another, defined as the second material, with density \(\rho _2\) and wave velocity \(c_2\), the stress \(\sigma _R\) and particle velocity \(v_R\) of the reflected wave in the first material are equal to:

As a model blast is carried without high-speed camera, the whole blasting process is invisible. Accordingly, it is unknown whether the model is thrown or not during blasting. If model blasts aim to study detonation behavior or measure detonation pressure, specimen placement may not markedly affect the measurement since the detonation will be over before the model is thrown. However, the placement will influence rock fragmentation in the late stage of blasting. Therefore, specimen placement should be considered in all kinds of model blasts. No matter which kind of specimen placement is to be used, a simple stress wave analysis, as conducted in this paper, is needed before model blasting so that the effect of specimen placement on blast result can be estimated and limited to a small range.

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