Schoold of Mechanical and Mining Engineering

A new model to predict the extent of crushing around a blasthole is presented. The model is based on the back-analysis of a comprehensive experimental program that included the direct measurement of the zone of crushing from 92 blasting tests on concrete blocks using two commercial explosives. The concrete blocks varied from low, medium to high strength and measured 1.5 m in length, 1.0 m in width and 1.1 m in height. A dimensionless parameter called the crushing zone index (CZI) is introduced. This index measures the crushing potential of a charged blasthole and is a function of the borehole pressure, the unconfined compressive strength of the rock material, dynamic Young's modulus and Poisson's ratio. It is shown that the radius of crushing is a function of the CZI and the blasthole radius. A good correlation between the new model and measured results was obtained. A number of previously proposed models could not approximate the conditions measured in the experimental work and there are noted discrepancies between the different approaches reviewed, particularly for smaller diameter holes and low strength rock conditions. The new model has been verified with full scale tests reported in the literature. Results from this validation and model evaluations show its applicability to production blasting.

A combination of preconditioning by hydraulic fracturing and confined blasting referred to as intensive preconditioning has been implemented for the first time at a major panel caving operation. The reasoning behind this application was the potential to alter rock mass behaviour in a manner that could improve caving mechanics and overall extraction performance. A comprehensive sampling and testing campaign was conducted before and after the application of large scale intensive preconditioning. Intact rock data was analysed with the combined use of uniaxial compressive strength tests and acoustic emission monitoring. The aim was to define damage thresholds of intact rock and study specific boundaries associated with different degrees of preconditioning. To evaluate the intact rock failure process, four stages or damage were studied, they included crack initiation stress, crack damage stress, uniaxial peak strength and cumulative count of Acoustic Emission (AE) events. Results from this analysis indicated that between in situ and post hydraulic fracturing preconditioning, the initiation of damage occurs almost at the same stress levels, which as expected, demonstrated that hydraulic fracturing does not affect intact rock strength. However, after preconditioning by confined blasting, results indicated that the onset of excessive damage prior to failure was occurring at lower axial stresses, this confirmed the presence of micro-fractures in the samples which may be attributed to confined blasting induced stresses.

ANFO is a well-known, reliable and safe commercial explosive. It has been around since the late 1950's and its detonation properties are well characterized. In this study, the detonation process of dry, wet and aluminised ANFO, was recorded using two high-speed cameras with recording rates of 1,200 fps and 50,000 fps. The 1,200-fps footage allowed the observation of the post blast fumes (i.e. NOx) produced by ANFOs with different water contents. The 50,000-fps footage allowed the observation of the detonation area, gas expansion phase and the measurement of the velocity of detonation (VOD). The video footage also recorded a bright zone in front of the gases (longer than 50 mm). We assumed that a reaction is taking place in this zone, but it is difficult to be sure if this is the reaction zone or not as it is longer than previously reported reaction zone lengths. Analysis showed that ANFO detonates effectively for water contents of up to 9 wt.%, and more importantly, there is little variation in the VOD. As far as the expansion of gases is concerned, the ANFO-Al expansion rate appears to be different. In this mixture, the absence of NOx fumes could have been due to the expected higher temperatures produced by the burning of the aluminium additive as observed in the images recorded with the high-speed camera.

Mining explosives based on ammonium nitrate(V) are safe and effective, however, the risk of NOx fume production during blasting is still present. In 2013, a project to eliminate NOx fumes from blasting began and hydrogen peroxide was chosen to replace ammonium nitrate(V) as the oxidiser. Previous work in this area demonstrated that hydrogen peroxide/fuel-based mixtures were able to detonate, provided that they are initiated under a situation of high confinement and also using hydrogen peroxide at relatively high concentrations. In contrast, a comprehensive study was conducted to determine the detonation properties of hydrogen peroxide/fuel-based mixtures that used hydrogen peroxide at lower concentrations (below 50 wt.%), detonated in unconfined conditions and used void sensitisation to achieve an efficient detonation reaction. This article presents the results of the influence of the density, water content, critical diameter and type of void sensitisation on the velocity of detonation (VOD) of hydrogen peroxide/ fuel-based explosive mixtures. The results indicate that the mixtures can achieve a different VOD which depends on the size of the sensitising voids and more importantly, the mixtures behave as non-ideal explosive, similarly to ammonium nitrate-based explosives, but with the advantage of being a NOx-free explosive.

A better understanding of the detonation performance of an explosive charge can be gained by directly measuring pressure, temperature and velocity of detonation (VOD). This is particularly important with explosives used in the mining industry because their performance is directly influenced by the degree of confinement. A project funded by the Australian Coal Association Research Program was initiated in early 2009 with the view to design and build cost effective prototype instrumentation to measure the relative differences in detonation pressures and temperatures of commercial mining explosives. The project's primary focus was on low density explosives as their detonation performance is not well understood. It was therefore viewed as important to be able to directly measure pressure and temperature during the detonation process of these complex mixtures in production blastholes. The paper describes the prototype instrumentation developed and reports on the results obtained to date in laboratory and full scale conditions

Image analysis as a technique for fragmentation measurement of rock piles has been the subject of research since the 1980's and to date, run of mine (ROM) fragmentation optimisation studies have primarily relied on particle size measurement using photographic based 2D imaging systems. Disadvantages of 2D imaging systems include particle delineation errors due to variable lighting and material colour and texture variation; no direct measure of scale & perspective distortion; and inability to distinguish overlapped particles, non-overlapped particles and areas-of-fines. With the development of 3D imaging technologies, there is an opportunity to develop techniques that could improve data collection and overcome the limitations of existing 2D image based systems. This paper describes the first attempt to use 3D high resolution laser scanning techniques to quantify "whole of muckpile" fragmentation from full scale production blasting. During two monitoring campaigns in 2013, high resolution laser scanning data was collected from production blasts at Esperanza Mine (Antofagasta Minerals Group). Fully automated analysis of the 3D data was possible in all cases where the data was of sufficiently high resolution. Manual pre-processing was required when the data was of low resolution to specify the region of fines. Overall results indicated that run of mine fragmentation requirements were meeting specified targets despite the marked differences in powder factors. This was particularly the case for those blasts conducted in similar geological domains. This work has demonstrated that high resolution laser scanning can be used as an alternative technique to measure "whole of muckpile" fragmentation in production blasting.

Recent developments have indicated that explosive mixtures of hydrogen peroxide (HP) and fuel exhibit detonation performance characteristics that could potentially make them viable for use in the civil and mining industries to fragment rock. Further development of the technology has also involved the study of hybrid mixtures containing combinations of HP and nitrates in the oxidiser phase of the detonation performance of the explosives. Performance was characterised by both detonation modelling and a series of fully instrumented unconfined velocity of detonation (VOD) tests. Analysis showed some interesting differences in the velocity of detonation between the hybrids using Na + , NH4 + and Ca +2. Hybrid mixtures of peroxide with sodium nitrate showed that even though there is theoretically more energy available, field results indicate that this extra energy does not translate into higher velocities of detonation for a range of densities. Additionally, variation in the charge of the cation in the nitrate (i.e. Na + , Ca +2) does not translate into a significate difference in VOD, which suggests that cation charge does not influence detonation performance. Some hypotheses are offered to explain this behaviour.

Since 2001, the Hybrid Stress Blast Model (HSBM) project members have developed a software suite to model the complete blasting process from non-ideal detonation to muck pile formation. To preserve the physics and improve solution time, the breakage engine uses a combination of analytical models and 2D axisymmetric finite differences to model near-field crushing, coupled to 3D discrete lattice fracturing and distinct element numerical methods to model throw and muck pile development. The model has been validated by comparison with laboratory and field tests in kimberlite. Multiple blasthole simulations are used to demonstrate how changes to blasting parameters can influence downstream efficiencies. Case studies of wall control blasting show that the presplit design must balance the two opposing effects of increased damage with increased charge and decreasing attenuation of the seismic waves with decreasing charge. Modelling of decoupled explosives needs further development. Reducing...

The mining industry faces diverse challenges to maintain sustainable production, particularly regarding critical water and energy supplies. As a significant player in the copper mining industry, Chile has become a global reference. Therefore, this research analyses the distinct challenges of the Chilean copper mining industry in terms of water and energy. We also identified ten key challenges that the Chilean copper mining industry must address to remain competitive and relevant. Several mining companies were examined to review and understand the different types of Environmental Management Initiatives (EMIs) adopted. The most prevailing strategies involved implementing Environmental Management Systems, which allow organisations to define, implement, and track their specific goals and standards. This review acknowledged four relevant water-related initiatives, including seawater use, community strategic plans, general environmental monitoring programs, and water recycling and recircu...

Yogurt-a milk based mix fermented by lactic acid bacteria is a valuable health food for both young and old. Milk is the main ingredient of yogurt. However, most yogurts contain additional solids such as milk solids nonfat to boost the nonfat milk solids. Stabilizers such as natural gums are added to improve and maintain gel firmness and consistency, while also for many people to improve appearance and mouth feel. Hydrocolloids specifically stabilize gel structure, increase viscosity and either from networks with milk constituents and establish a separate gel structure. In current research, a natural local plant Iranian hydrocolloid, cress seed gum, is added to yogurt formulation and its rheological properties are evaluated using a rotational viscometer. Different famous rheological models have been used to fit shear stress-shear rate data's. The results demonstrated that cress seed gum has a good potential to be used as a stabilizer in yogurt formula.

The present invention provides an explosive composition comprising from about 2 to about 25 % w/w hydrogen peroxide, from greater than 0 and up to about 90 % w/w of one or more of other oxidisers. The present invention also provides a method of 5 preparing an explosive composition and use of the explosive composition of the invention to break and move ground, such as in mining operations