Improving Collar Zone Fragmentation by Top Air-Deck Blasting Technique

Air gap in an explosive column has long been applied in open-pit blasting as a way of reducing explosive charge, vibration, fly rock and improve fragment size. In conventional blasting a greater amount of explosive energy is lost in the generation of oversize fragments. Oversize fragments reduces loading and hauling efficiencies of equipment which requires secondary blasting. Recurring oscillation of shock waves in the air gap increases the time over which it acts on the adjacent rock mass by factor of 2–5. Top air deck blasting technique trial conducted with an application of gas bags at Chimiwungo pit resulted in an improved fragmentation of about 94 % less than 950 mm. Results obtained from the analysis of muckpile images using split-desktop exhibited that the mean fragment size was 264.81 mm and F20, F80 and top-size were 41.99, 683.18 and 1454.69 mm respectively. Optimum crusher feed size was as large as 1200 mm and crushed down to the 40 mm and only a small percent of the material was above 1200 mm. Gas bag application resulted in a significant reduction in explosives load in production holes without loss in fragmentation or movement of the collar zone. This reduced total cost of charging as compared to conventional blasts with a variance of $20, powder factor was dropped to an average of 0.86 kg/bcm. The technique reduced the cost of bulk blend explosive by 15 %, reduced overall cost of charging per hole by 12 %, enhanced premature ejections. The overall blast results were satisfactory, 443,624 tonnes of blasted material from the block which represented 90 % of the total muckpile material was within 900 mm size. The overall muckpile blasted was well fragmented.     

Influence of Gassing Agent and Density on Detonation Velocity of Bulk Emulsion Explosives

The demand for coal from surface mining projects are on the higher side like never before for which blasting is the basic unit operation. The explosive plays an important role in blasting and also influence the explosive-rock interaction. The most common explosive type used in surface mines is emulsion explosives. This paper presents the study on the detonation velocity of bulk emulsion explosives due to variation in gassing agent and density. In this study Sodium Nitrite (NaNO₂) has been used as the gas generating additive and the performance of emulsion explosives with different concentrations of gassing agents at different temperatures has been observed. This study was undertaken to also understand the cyclic variation of temperature on gassing kinetics and performance of explosive. The effect of cooling on detonic-behaviour of bulk emulsion explosives has also been studied and presented in this paper.     

What Causes Cracks in Rock Blasting?

In blasting, a few or many cracks are driven from the borehole into the rock. But what causes the cracks? The most common theory of breakage consists of two stages; first the shock wave causes radial cracks to form around the hole then the gases penetrate into the cracks, and widen them and make them longer. Another theory presented by Brinkmann suggests that the back damage is primarily controlled by shock and that the gas penetration is the mechanism controlling breakout of the burden. He did his experimental work using blasthole liners. Recent research at SveBeFo has examined this matter further. In a quarry a number of benching holes have been blasted simultaneously. In some of these holes tubular Swellex bolts were inflated and decoupled charges put inside the tubes without stemming. Other holes were identically charged but without the lining. Finally some holes were also stemmed. After blasting the cracks in the remaining rock were studied. There was no difference in crack lengths between holes charged normally (no stemming) and holes where the charges were inside the bolts. On the other hand when stemming was used, the crack lengths increased for some explosives but remained the same for an emulsion explosive. In another set up blasted granite blocks were charged in the same way as above. Then we could also measure the bore hole pressure. The pressure gauge consists of a small carbon resistor inside a steel cylinder. It is called LHM (Location-fixed Hydrodynamic Measuring cup) and is placed at the bottom of the hole. A smaller exit hole from the bottom is drilled for the cables. The paper presents the technique and the results obtained from both the quarry blasting and the blasting of the blocks.     

岩石中柱状装药爆炸能量分布

岩石中装药爆炸产生的爆破能量可分为爆炸冲击波能量和爆生气体膨胀能量。对爆炸能量分布的理论分析有助于改善爆破效果,提高爆破质量。在柱状耦合装药情况下,分析了冲击波作用下岩石变形和破坏的特点、爆生气体对爆腔的扩腔作用,考虑了在岩体的损伤情况下爆生气体对裂纹的驱裂作用。计算结果表明：埋深在临界深度以下时,岩石中柱状装药爆破冲击波做功消耗的能量约占爆炸总能量的40 %,剩余爆生气体能量中用于扩腔和扩展主要裂隙的能量约占总能量的23 %,剩余大约37 %的能量中有小部分能量用于新增裂纹数目,而大部分损失掉了。     

Fragmentation Energy in Rock Blasting

The theoretical explosive energy used in blasting is a common issue in many recent research works (Spathis 1999; Sanchidrian 2003). It is currently admitted that the theoretical available energy of the explosives is split into several parts during a blast: seismic, kinetic, backbreaks, heave, heat and fragmentation energies. Concerning this last one, the energy devoted to the breakage and to the creation of blocks within the muckpile can be separated from the microcracking energy which is devoted to developing new and/or extending existing micro cracks within the blocks (Hamdi et al. 2001; López et al. 2002). In order to investigate these two types of energy, a first and important task is to precisely study the main parameters characterising the two constitutive elements of the rock mass (rock matrix and discontinuity system). This should provide useful guidelines for the choice of the blasting parameters (type of explosive, blasting pattern, etc.), in order to finally control the comminution process. Within the frame of the EU LESS FINES research project, devoted to the control of fines production, the methodology was developed in order to: (1) characterize the in situ rock mass, by evaluating the density, anisotropy, interconnectivity and fractal dimension of the discontinuity system and (2) evaluate fragmentation (both micro and macro) energy spent during the blasting operation. The methodology was applied to three production blasts performed in the Klinthagen quarry (Sweden) allowing to estimate the part of the fragmentation energy devoted to the formation of muck pile blocks on one side and to the muckpile blocks microcracking on the other side.     

不耦合装药下爆炸应力波传播规律的试验研究

通过室外爆破试验,利用预埋研制的PVDF压力传感器对耦合及水不耦合延长药包装药爆破时爆炸应力波的中远场压力进行测量,拟合实测结果,得到4种不耦合系数下爆炸应力波峰值随传播距离衰减的指数关系式。分析试验结果可知： ①在试验所涉及的范围内,不耦合装药时爆破应力波峰值衰减幅度小于耦合装药（即K =1）时爆破应力波峰值衰减幅度,验证了水介质作为炸药爆轰产物与岩体间的弹性缓冲层作用,减少了粉碎孔壁岩体造成的能量耗散,增加了能量传递,加大了爆炸的作用范围;②当不耦合系数K = 3.29时,应力波峰值衰减指数表现出大于K =1.79及大于K =2.57时应力波峰值衰减指数的趋势,表明过大的不耦合系数造成了不耦合介质--水过多的能量耗散（在高温高压下水并不完全是弹性的）,削弱了不耦合装药爆破的优势;③在不耦合装药爆破中,存在最佳的不耦合系数,此时爆炸应力波峰值衰减最慢,爆炸能得到充分利用,达到最优的爆破效果。研究结果对不耦合装药爆破的设计及工程应用有一定的指导意义。     

A Statistical Approach to Predict the Effect of Confinement on the Detonation Velocity of Commercial Explosives

Summary Commercial explosives behave non-ideally in rock blasting. A direct and convenient measure of non-ideality is the detonation velocity. In this study, an alternative model fitted to experimental unconfined detonation velocity data is proposed and the effect of confinement on the detonation velocity is modelled. Unconfined data of several explosives showing various levels of non-ideality were successfully modelled. The effect of confinement on detonation velocity was modelled empirically based on field detonation velocity measurements. Confined detonation velocity is a function of the ideal detonation velocity, unconfined detonation velocity at a given blasthole diameter and rock stiffness. For a given explosive and charge diameter, as confinement increases detonation velocity increases. The confinement model is implemented in a simple engineering based non-ideal detonation model. A number of simulations are carried out and analysed to predict the explosive performance parameters for the adopted blasting conditions.     

关于岩体爆破研究的几点思考

为研究和探索爆炸荷载与岩体相互作用的本质,运用能量守恒、系统论和复杂性理论,阐述了岩体爆破过程中的几个重要问题,即炸药与岩体的相互匹配、岩体爆破的系统性和复杂性问题。     

A Further Study on the Mechanism of Airdecking

Airdecking is used in mining for two quite different applications. One is to enhance the fragmentation by amplifying the induced fracturing and the second is for pre-split blasting in which the borehole fracturing is reduced. This paper deals with the first of these effects. A forth coming paper will describe pre-splitting by airdecking. The use of air decks to enhance rock fragmentation and so to reduce explosive costs has been the practice for quite long time. Although a number of studies has been conducted to verify the advantages of blasting with air decks and to investigate the mechanisms involved, the proposed mechanisms still cannot explain clearly the phenomena observed in practice and the design approach adopted for this kind of blasting is still primary based on rules-of-thumb. In this paper, the theory of shock tubes is adopted to (a) investigate the processes of the expanding detonation products, (b) study the interactions between the explosion products and the stemming or bottom of blasthole, and (c) to decide the distribution of the changing pressure of explosion products along blasthole. Numerical simulation and theoretical analyses are then performed to study the physical process of blasting with air decks. Finally, a reasonable value for the airdecking ratio is decided theoretically. It is shown that the pressure-unloading process caused by the propagation of the rarefaction wave and the reflected rarefaction waves in the detonation products plays an important role in the enhanced fragmentation of rock when blasting with air decks. The unloading process can induce tensile stresses of rather high magnitude in the rock mass surrounding blasthole. This favors fracturing of the rock. The reflected shock wave with a magnitude of gas pressure higher than that of the average detonation pressure in a fully charged blasthole acts as the main energy source to break the rock in the air deck and stemming portions. The second and succeeding strain waves induced by the unloading or reloading of the pressurewithin the blasthole also contribute to form the initial fracture network in the rock around the blasthole. It is also revealed that there exists a reasonable range of values for the airdecking ratio. For ANFO, this value varies from 0.13-0.40.     

Incremental explosive energy distribution in blasting design

Summary The increasing range of explosive types and methods of initiation available to the blasting design engineer, and the possibilities of obtaining more detailed rock property data, require improvements in the precision of blasting design methods. Average design values, such as powder factor and specific charge, have little significance where rock properties vary in any lithological section of the blast. Application of the concept of incremental explosive energy distribution will increase the design sensitivity and control over blastability variations. In this paper the use of this concept is described for different levels of complexity. These range from the simple allocation of explosive energy for large rock sections, to the use of more complex energy attentuation functions to allocate incremental specific energy levels. Procedures to develop rock fragmentation predictions from such data are also outlined.     

Fragmentation prediction using improved engineering formulae

In the last decade, fragmentation prediction has been attempted by many researchers in the field of blasting. Kuznetsov developed an equation for the estimation of average fragment size, x 50 , based on explosive energy and powder factors. Cunningham introduced a uniformity index n as a function of drilling accuracy, blast geometry and a rock factor A associated with a “blastability index”, which can be calculated from the jointing, density and hardness of the blasted rock mass. Knowing the mean size and the uniformity index, a Rosin-Rammler distribution equation can then be derived for calculating the fragment size distribution in a blasted muckpile. Analysis of existing data has revealed serious discrepancies between actual and calculated uniformity indices. The current integrated approach combines the Kuznetsov or similar equation and a comminution concept like the Bond Index equation to enable the estimation of both the 50% and 80% passing sizes ( k 50 and k 80 ). By substituting these two passing sizes into the Rosin-Rammler equation, the characteristic size x c and the uniformity index n can be obtained to allow the calculation of various fragment sizes in a given blast. The effectiveness of this new fragmentation prediction approach has been tested using sieved data from small-scale bench blasts, available in the literature. This paper will cover all tested results and a discussion on the discrepancy between measurement and prediction due to possible energy loss during blasting.     

爆破工程地质控制论

爆破理论与技术的创新和发展,对我国爆破工程事业乃至基础设施建设都是十分重要的。在数十年爆破理论研究与生产实践的基础上,对爆破及其破岩的科学概念进行了定义,系统阐述了炸药能量特征、岩体介质特征、炸药能量与岩体介质相互作用等决定爆破作用机制和效果的因素及其相互关系,明确指出地质条件是爆破的基础,炸药能量特征必须与岩体介质特征来适应;基于岩体特性及其爆破特征,将自然岩体划分为似均匀连续体和不连续体两类。研究表明,在似均匀连续体中,岩体爆破作用机制和效果受微地形最小抵抗线控制;在不连续体中,受岩体结构特征控制。两者结合,形成了爆破工程地质控制论。     

A Review of General Considerations for Assessing Rock Mass Blastability and Fragmentation

Blasting is the primary comminution process in most mining operations. This process involves the highly complex and dynamic interaction between two main components. The first is the detonating explosive and the second is the rock mass into which the explosive is loaded. The mechanical properties of the rock material (such as dynamic strength, tensile strength, dynamic modulus and fracture toughness) are important considerations in understanding the blasting process. However, it is the characteristics of the geological defects (joints, foliation planes, bedding planes) within the rock mass that ultimately determine how effectively a blast performs in terms of fragmentation, all else being equal. The defect characteristics include, but are not limited to, their orientation, spacing, and mechanical properties. During the blasting process, some of the geotechnical characteristics of the rock mass are substantially changed. From the blasting outcome point of view, the most notable and important is the change in fragment size distribution that the rock mass undergoes. The pre-blast in situ defect-bounded block size distribution is transformed into the post-blast muckpile fragment size distribution. Consequently, it is fundamental to our understanding of and ability to predict the blasting process that both the blastability of a rock mass and its transformation into the fragment size distribution can be appropriately quantified.     

立井冻土掘进爆破技术的研究与应用

崩落爆破通常承担整个立井冻土掘进爆破40 %～60 %的破土量。宽孔距崩落爆破能够增加自由面的有效利用、增强自由面应力波的反射拉伸作用和消除或减小冻土中的应力降低区。在理论分析的基础上进行冻土爆破漏斗模型试验,综合考虑爆破漏斗体积和爆破后两炮眼间最大凸量,初步认为炮眼密集系数 =1.5左右时较为合理。结合立井崩落炮眼成圈弧形布置和冻土所受夹制作用相对较大的特点,建议应在此基础上适当降低立井冻土崩落爆破炮眼密集系数,这在进一步的工程实践中得到了验证。     

水下岩石爆破参数优化的研究

分析了水下岩石工程爆破技术的发展现状，通过对各方面影响因素的研究分析，认为影响水下岩石爆破炸药单耗的主要因素是岩石的RQD，水深H及岩性因素f，推导出了水下岩石爆破炸药单耗q的公式。     

The application of size distribution equations to rock breakage by explosives

SummaryThe Application of Size Distribution Equations to Rock Breakage by Explosives Size distribution equations can be used to describe the degree of fragmentation produced by explosive rock breakage. This paper describes the results of small scale blasting experiments and the derivation of equations to relate size distributions to blasting design parameters. The application and relevance of these techniques to large scale blasting operations is also discussed.With 7 Figures     

A Non-Ideal Detonation Model for Evaluating the Performance of Explosives in Rock Blasting

Summary  A new model to predict the non-ideal detonation behaviour of commercial explosives in rock blasting is presented. The model combines the slightly divergent flow theory, polytropic equation of state, simple pressure-dependent rate law and statistical expressions to model the effect of confinement on detonation. The model has been designated as DeNE, an acronym for the Detonics of Non-ideal Explosives. It is aimed at predicting the detonation state and subsequent rarefaction (Taylor) wave to provide the pressure history for different explosive, rock type and blasthole diameter combinations. It enables the prediction and comparison of the performance of commercial explosives in different blasting environments. The unconfined detonation velocity data has been obtained from the testing of six commercial explosives to calibrate DeNE. A detailed sensitivity analysis has been conducted to evaluate the model. The model has been validated using the results of hydrocodes as well as measured and published in-hole detonation velocity data. Author’s address: Sedat Esen, Metso Minerals Process Technology (Asia-Pacific), Unit 1, 8–10 Chapman Place, Eagle Farm, Qld 4009, Australia     

Evaluation of initiating system by measurement of seismic energy dissipation in surface blasting

Enhanced demand for coal and minerals in the country has forced mine operators for mass production through large opencast mines. Heavy blasting and a large amount of explosive use have led to increased environmental problems, which may have potential harm and causes a disturbance. Ground vibrations generated due to blasting operations in mines and quarries are a very important environmental aspect. It is clear that a small amount of total explosive energy is being utilized in blasting for breakage of rock mass, while the rest is being wasted. The amount of energy which is wasted causes various environmental issues such as ground vibrations, air overpressure, and fly rock. Ground vibrations caused by blasting cannot be eliminated entirely, yet they can be minimized as far as possible through a suitable blasting methodology. A considerable amount of work has been done to identify ground vibrations and assess the blast performance regarding the intensity of ground vibrations, i.e., peak particle velocity and frequency spectrum. However, not much research has done into reducing the seismic energy wasted during blasting leading to ground vibrations. In this paper, the blast-induced ground vibrations in three orthogonal directions, i.e., transverse, vertical, and longitudinal, were recorded at different distances using seismographs. An attempt has been made for the estimation of the percentage of explosive energy dissipated in the form of seismic energy with electronic and non-electric (NONEL) initiation system. signal processing techniques with the help of DADiSP software is used to study the same.     

新型大孔径静态破碎技术的试验研究

在传统静态爆破的基础上,提出了一种新型大孔径静态爆破技术,使用新型扩孔钻头结合机械堵孔器解决了大孔径静态爆破的冲孔问题。由于孔径的增大,使得破碎剂膨胀压力增大,膨胀剂反应速度加快,加大了堵孔难度。设计的新型扩孔钻头和新型堵孔器进行了孤岩块的大孔径静态爆破试验,试验结果证实了该新型大孔径静态爆破技术的可行性,达到了提高爆破能力和缩短破坏时间的预期目的。为今后的敏感地区岩石爆破工程开挖提供了新途径。     

节理岩体爆破的DDA方法模拟

在非连续变形分析（DDA）方法中,通过跟踪炮孔扩张和炮孔周边裂隙的发展贯通求得爆腔的即时体积,进而根据爆生压力状态方程计算爆腔即时压力,并将爆生压力载荷作用到主炮孔内壁和贯通裂隙面上,实现了爆生产物作用下节理岩体爆破的DDA方法模拟。采用DDA方法模拟了节理岩体中的水平柱状炮孔抛掷爆破问题,得到了爆腔的体积扩张和压力衰减时间曲线,模拟很好的再现了岩石爆破过程中的炮孔扩张、岩体破坏、块体抛掷和爆堆形成过程。