An innovative priming system - emulsion-based booster

The mineral industry is leading towards a technology driven optimization process. Drilling and blasting are such unit operations in a mine, which can alter the balance sheet of the mine if not planned properly. The development, improvement and utilization of innovative technologies in terms of blast monitoring instruments and explosives technology are important for cost effectiveness and safety of mineral industries.

The ever-growing demand for minerals has compelled the industry to adopt large opencast projects using heavy equipment. This has necessitated use of a few hundred tonnes of explosives in each blast. The bulk delivered fourth generation explosives have solved the problem of explosive loading to a large extent as it provides improved safety in manufacturing, transportation and handling. Bulk delivered emulsion is non-explosive until gasification is complete and a large quantity of explosive can be transported and loaded into blast holes efficiently and with safety. The priming of bulk delivered explosives in Indian mines uses the conventional PETN/TNT-based boosters. The conventional booster possesses safety problems in terms of handling and use, so Indian Explosives Ltd has developed an emulsion-based booster (Powergel Boost).

This paper explores the potential of an emulsion-based booster used as a primer to initiate bulk delivered emulsion explosives used in mines. An attempt has been made at a comparative study between the conventional booster and the emulsion-based booster in terms of the initiation process developed and their capability of developing and maintaining a stable detonation process in the column explosives. The study has been conducted using a continuous velocity of detonation (VOD) measuring instrument, the VODMate two channel system manufactured by Instantel Inc. of Canada. During this study three blasts were monitored. In each blast two holes were selected for study, the first hole was initiated using a conventional booster while the other one used an emulsion-based booster. The findings of the study advocates that the emulsion-based booster is capable of the efficient priming of bulk delivered column explosive with a stable detonation process in the column.     

Variable Energy Explosives for Soft Ground Blasting

A range of bulk explosives, the NOVALITE range hay been specifically developed for soft ground blasting. These explosives can be used in both wet and dry blasting conditions, range in density from 0.3-1.2 g/cc and range in VoD from 2-4.5 km/s. This range of explosives hay the potential to be tailored to ground type and is predicted to be suitable for a variety of applications which include: blasting in soft to medium overburden, coal blasting, wall control, and low vibration blasting. Trials have been conducted in several applications with encouraging results. Several cast/throw blasts have been conducted with these products partially replacing either ANFO or Heavy ANFO. The results from the blast have been equivalent in cast (per cent) and at reduced cost per unit volume. These products have also been used in presplit blasting and have again achieved equivalent or better results when compared to conventional presplit blasting at a lower cost per unit volume. This product has also been used in a vibration sensitive area replacing traditional explosive products, and generating excellent fragmentation and digging whilst maintaining vibration limits. This new range of products, NOVALITE, has shown great potential in many applications either reducing cost per unit volume, improving wall quality or improving productivity in environmentally sensitive areas.     

Analysis of the Effect of Borehole Size on Explosive Energy Loss in Rock Blasting

In this paper, studies were conducted on the effect of borehole size on explosive energy loss in rock blasting. Since most industrial explosives are nonideal ones, the charge size and the confinement condition have significant impact on the detonation performance of these explosives. Analyses indicated that smaller boreholes will cause more loss of explosive energy than larger ones. This is especially true for most industrial explosives. The paper presents the analyses of energy loss for a number of different explosives with various borehole sizes. Based on these analyses recommendations and guidelines were given for borehole size determination in rock blasting operations.     

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     

Comparative study of analytical and numerical evaluation of the dynamic response of buried pipelines to road-cut excavation blasting

ABSTRACT

This study develops a mathematical model of buried pipelines subjected to surface blast loading based on the theory of beam on elastic foundation. The Fourier transform, a mathematical formula that converts the time domain of the problem to the frequency domain, was used in order to solve a fourth-order non-homogeneous partial differential equation. Transforming the solution back to the time domain, the blast-induced Peak Particle Velocity (PPV) of the pipeline can be calculated. In addition to the mathematical model, a three-dimensional finite element model has been established, thereby drawing a comparison between analytical and numerical results. It can be concluded that the analytically calculated PPV values are found to be higher than the corresponding numerical values. Lastly, the safe distance from the pipeline to blast source and the maximum allowable ANFO explosive weight for two types of rock have been presented in the form of graphs by imposing a limit of 50 mm/s for PPV. This comparative study has investigated the effect of road-cut excavation blasting on pipelines buried under only two types of rock mass. However, it can be used for different types of rock and explosives, mainly thanks to the comprehensiveness of the analytical solution.     

Multivariate statistical analysis approach for prediction of blast-induced ground vibration

Excavation of coal, overburden, and mineral deposits by blasting is dominant over the globe to date, although there are certain undesirable effects of blasting which need to be controlled. Blast-induced vibration is one of the major concerns for blast designers as it may lead to structural damage. The empirical method for prediction of blast-induced vibration has been adopted by many researchers in the form of predictor equations. Predictor equations are site specific and indirectly related to physicomechanical and geological properties of rock mass as blast-induced ground vibration is a function of various controllable and uncontrollable parameters. Rock parameters for blasting face and propagation media for blast vibration waves are uncontrollable parameters, whereas blast design parameters like hole diameter, hole depth, column length of explosive charge, total number of blast holes, burden, spacing, explosive charge per delay, total explosive charge in a blasting round, and initiation system are controllable parameters. Optimization of blast design parameters is based on site condition and availability of equipment. Most of the smaller mines have predesigned blasting parameters except explosive charge per delay, total explosive charge, and distance of blast face from surface structures. However, larger opencast mines have variations in blast design parameters for different benches based on strata condition: Multivariate predictor equation is necessary in such case. This paper deals with a case study to establish multivariate predictor equation for Moher and Moher Amlohri Extension opencast mine of India. The multivariate statistical regression approach to establish linear and logarithmic scale relation between variables to predict peak particle velocity (PPV) has been used for this purpose. Blast design has been proposed based on established multivariate regression equation to optimize blast design parameters keeping PPV within legislative limits.     

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.     

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.     

Finite element analysis of vibrations induced by propagating waves generated by tunnel blasting

Summary The excavation of underground tunnels close to existing substructures or the ground surface presents problems especially when blasting is being carried out. The high intensity waves which are generated and propagated through the rock medium, due to the detonation of explosives, may still have large amplitudes when they reach the ground surface. In order to study the vibration effects due to these propagating waves associated with blasting, a finite element simulation of tunnel blasting has been carried out in this paper.An example of a new tunnel excavated below an existing tunnel has been studied. Even though this problem is three dimensional in nature, due to the large computational efforts involved in three dimensional dynamic analysis, a two dimensional finite element analysis has been adopted. A pseudo-plane strain concept has been used since it has been found that the results obtained using such an approach are more realistic than the conventional plane strain analysis.It is concluded that results from such a numerical analysis could compliment the field investigations to produce guidelines for safe and controlled blasting.     

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.     

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.     

Theory and Practice of Air-Deck Blasting in Mines and Surface Excavations: A Review

The mechanism by which the explosive energy is transferred to the surrounding rock mass is changed in air-deck blasting. It allows the explosive energy to act repeatedly in pulses on the surrounding rock mass rather than instantly as in the case of concentrated charge blasting. The air-deck acts as a regulator, which first stores energy and then releases it in separate pulses. The release of explosion products in the air gap causes a decrease in the initial bore hole pressure and allows oscillations of shock waves in the air gap. The performance of an air-deck blast is basically derived from the expansion of gaseous products and subsequent multiple interactions between shock waves within an air column, shock waves and stemming base and shock waves and hole bottom. This phenomenon causes repeated loading on the surrounding rock mass by secondary shock fronts for a prolonged period. The length of air column and the rock mass structure are critical to the ultimate results. Several attempts have been made in the past to study the mechanism of air-deck blasting and to investigate its effects on blast performance but a clear understanding of the underlying mechanism and the physical processes to explain its actual effects is yet to emerge. In the absence of any theoretical basis, the air-deck blast designs are invariably carried out by the rules of thumb. The field trials of this technique in different blast environments have demonstrated its effectiveness in routine production blasting, pre-splitting and controlling over break and ground vibrations etc. The air-deck length appropriate to the different rock masses and applications need to be defined more explicitly. It generally ranges between 0.10 and 0.30 times the original charge length. Mid column air-deck is preferred over the top and bottom air-decks. Top air-deck is used especially in situations, which require adequate breakage in the stemming region. The influence of air-deck location within the hole on blast performance also requires further studies. This paper reviews the status of knowledge on the theory and practice of air-deck blasting in mines and surface excavations and brings out the areas for further investigation in this technique of blasting.     

Lower blasthole pressures: a means of reducing costs when blasting rocks of low to moderate strength

Summary From a purely mechanical viewpoint, each explosive charge should produce a peak blasthole pressure (P _b ) that just fails to crush (i.e. pulverise or plastically deform) the rock which surrounds it. WhereP _b exceeds a critical value, some explosion energy is wasted in crushing an annular section of rock immediately around each charge. As a rock's dynamic compressive breaking strain decreases, so shouldP _b (Hagan, 1977b).This paper reviews information on, and anticipates the blasting performance of, bulk charges having effective densities which are as low as about 40% of that for ammonium nitrate fuel oil (ANFO). It also outlines the potential advantages of extending the reaction periods of charges, even to the extent that explosive reactions continue after the blasthole wall and stemming have started to move. The paper then proceeds to define situations in which the use of such lower-pressure charges is likely to result in greatest reductions in mining costs. Some methods of applying bulk charges having effective densities in the 0.3–0.8 g cm^–3 range and/or lower reaction rates are suggested.     

Blasting: Another environmental woe

The much increased use of explosives to move and extract rock masses in construction and mining over the past two decades has resulted in a plethora of complaints from the general public in areas of close proximity to public facilities, communication, and transportation systems. Air blasts and ground vibrations caused by explosive detonation can have desultory and damaging effects to public and private property, impose adverse effects on underground mining operations, and change the course of flow or effect the availability of surface and groundwater.Attempts to prevent damage and alleviate problems from blasting have been initiated by the federal and state governments by the promulgation of rules and regulations to prevent against vagrant and negligent blasting procedures. The Office of Surface Mining, Reclamation and Enforcement (OSMRE) provided regulations in the Federal Register on March 8, 1983, with particular reference to surface mining practices. Most of the states have adopted the OSMRE guidelines to enforce these rules and regulations.This article refers to surface mine blasting within the State of Alabama and describes some of the research efforts conducted by The University of Alabama, Department of Mineral Engineering, Tuscaloosa, Alabama, over the past several years. The article does not provide answers to the environmental problems caused by blasting but describes research activities in the past and present time frames. Although restricted to Alabama, the problem is worldwide.     

Comparative Study on Calculation Methods of Blasting Vibration Velocity

Due to the extreme complexities in rock blasting and difficulties in theoretical or numerical analysis, and the enormous consumption of explosives in mining and construction operations, empirical or semi-empirical formulae for blasting vibration velocity (BVV) were obtained from observations and measurements in field blast tests and are still widely used all over the world. This paper investigates the fitting degree and characteristics of several calculation methods for BVV based on 34 sets of data samples from 27 projects belonging to 4 types. The results indicate that both the cube-root scaling formula and the square-root scaling formula have relatively good fitting degree, while the multiple regression analysis can give the best fitting outcome if the sample space satisfies certain requirements. Whether the cube-root scaling formula or the square-root scaling formula is chosen to analyze the relationship between BVV and scaled distance depends on the average scaled distance under cubic-root scaling. If the average scaled distance is over 0.1, the cube-root scaling formula should be used; otherwise, the square-root scaling formula should be used. Bigger samples integrated from data samples of different projects but in the same type were then analyzed to get the empirical relations for different types of projects. The correlation coefficients of these relations are quite good, thus these relations can be used for reference in other similar projects. This paper then discusses the physical meanings of parameters in different formulae, sample selection and parameter choice for BVV. It suggests that the current calculation methods for explosive charge, blasting-to-monitoring distance and scaled distance need to be improved. It also concludes that the integrated BVV from velocity components in three-dimensions is more reasonable on a theoretical basis. It can yield good results in predicting the blasting vibration, and should be used as widely as possible.     

混凝土含水裂隙中爆炸压力传播的模型试验研究

爆炸作用下含水裂隙中水压力的分布及传播特征对分析含水裂隙岩体初始裂纹扩展机制具有重要意义。通过含水裂隙的混凝土室内爆炸试验,测量了爆炸时含水裂隙中的水压力,分析了含水裂隙中水压力的荷载特性及传播特征,并研究了裂隙张开宽度及爆炸药量对水压力荷载的影响。试验研究结果表明：爆炸作用下含水裂隙中水压力时程分布呈多峰波动分布,水压力来源包括爆源通过水介质直接传递的荷载及通过混凝土间接传递的荷载,且在不同裂隙长度,荷载峰值主要来源不同;相同装药条件下,含水裂隙中水压力随距爆源距离增大而迅速衰减,裂隙中同一位置水压力大小与裂隙张开宽度呈负相关;混凝土室内爆炸试验含水裂隙中水击波所带能量频谱主要集中在7.8～62.5 kHz,是一种高频信号。随距爆源距离的增加,能量分布向低频集中;水击波频带能量分布特征受爆炸药量及裂隙张开宽度的影响。当量为4.5 g TNT（三硝基苯）乳化炸药装药相比 8.1 g TNT乳化炸药装药爆炸时水击波高频信息更丰富;相同爆炸药量时,随混凝土中含水裂隙张开宽度的增加,水击波频带能量分布峰值呈现向中间频带移动的趋势。     

The mitigation of the vibration effects caused by tunnel blasts in urban areas: a case study in Istanbul

Ground vibrations generated by commercial explosives in tunnel construction may cause structural damage in urban areas. Therefore, suppressing the vibration effects and mitigating the possible hazard after blasting is important. We present a new method of controlled blasting that is environmentally friendly, and easy to utilize for tunnel construction. Small charges in this method are detonated sequentially to produce minimum side effects. The efficiency of the charges may be increased based on the previously monitored shots. This method is utilized in a tunnel construction in Istanbul with five experimental shots. In these experiments, the duration and also the quantity of explosives were carefully controlled. We were able to obtain better results with short durations (480 ms) instead of long durations (9,000 ms) although the vibration levels defined as peak particle velocity (PPV) became bigger while the quantity of the explosive charge increased from 3.088 to 9.264 kg.     

Application of Air Decks in Production Blasting to Improve Fragmentation and Economics of an Open Pit Mine

In blasting with air decks, repeated oscillation of shock waves within the air gap increases the time over which it acts on the surrounding rock mass by a factor at between 2 and 5. The ultimate effect lies in increasing the crack network in the surrounding rock and reducing the burden movement. Trials of air deck blasting in the structurally unfavourable footwall side of an open pit manganese mine has resulted in substantial improvements in fragmentation and blast economics. Better fragmentation resulted in improved shovel loading efficiency by 50–60%. Secondary blasting was almost eliminated. Use of ANFO explosive with this technique reduced explosive cost by 31.6%. Other benefits included reductions in overbreak, throw and ground vibration of the order of 60–70, 65–85 and 44% respectively. This paper reviews the theory of air deck blasting and describes in detail the air deck blast trials conducted in a manganese open pit mine in India. The blast performance data have been analysed to evaluate the benefits of air decking over conventional blasting.     

Blast Damage and Blast Dilution Control: The Application of Bulk Emulsion Systems at the WMC St Ives Junction Mine

The application of modern bulk emulsion explosive systems at an underground gold mine resulted in a 57% improvement in gold dilution. While this improvement is impressive and could be expected to be achieved at other sites, the work required to assess and demonstrate the benefits is painstaking. Forty-eight rings involving a total of approximately 50 000 tonnes of ore were monitored using various modern surveying instruments over a 6-month period. The geometric data included blasthole locations and deviation, and the cavity monitoring of stopes. Implementation of a bulk emulsion system not only provided logistical benefits but it also has the desirable explosive properties associated with reducing the effects of blast damage and blast dilution.     

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。