Production Blasts Research Articles

Measuring blast fragmentation at Esperanza mine using high-resolution 3D laser scanning

Image analysis as a technique for fragmentation measurement of rock piles has been the subject of research since the 1980s, 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 because of variable lighting and material colour and texture variation; no direct measure of scale and 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 were 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 were of sufficiently high resolution. Manual pre-processing was required when the data were of low resolution to specify the region of fines. Overall results indicated that ROM 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.

An Overview on Measurement-While-Drilling Technique and its Scope in Excavation Industry

Measurement-while-drilling (MWD) aims at collecting accurate, speedy and high resolution information from the production blast hole drills with a target of characterization of highly variable rock masses encountered in sub-surface excavations. The essence of the technique rests on combining the physical drill variables in a manner to yield a fairly accurate description of the sub-surface rock mass much ahead of following downstream operations. In this light, the current paper presents an overview of the MWD by explaining the technique and its set-up, the existing drill–rock mass relationships and numerous on-going researches highlighting the real-time applications. Although the paper acknowledges the importance of concepts of specific energy, rock quality index and a couple of other indices and techniques for rock mass characterization, it must be distinctly borne in mind that the technique of MWD is highly site-specific, which entails derivation of site-specific calibration with utmost care.

Effect of blast-induced vibrations on fill failure in vertical block mining with delayed backfill

Numerical modelling has long been used as a powerful tool for geomechanics mine design and analysis of such problems as ore dilution. Open stoping mining method with delayed backfill is generally employed for mining steeply dipping tabular ore deposits. Several authors reported that consideration of production blast vibrations on adjacent, exposed backfill faces is crucial for the effective backfill design for minimum ore dilution due to fill failure. In this study, it is shown that blast vibrations can be characterized with dynamic numerical modelling. A FLAC3D dynamic numerical model has been developed for a typical layout of a secondary stope that is being mined next to a previously mined and backfilled primary stope. The numerical simulations are validated by comparing predicted failure geometry with laser-surveyed stope profiles obtained with a cavity monitoring system. It is shown that blast-induced vibrations can be a primary cause for wedge-type failure of the backfill face.

Controlled blasting for long term stability of pit-walls

Controlled blasting techniques were used to control over-breaks and to aid in the stability of the remaining rock mass at Rampura Agucha open-pit mine in India. The mine is a lead zinc mine producing 5.95mtpa of ore and has recently started its underground part, which is slated to produce 4.5mtpa of ore in near future. The mine is currently working at 260m depth, and is designed to reach a depth of 372m. During blasting, back break was the main concern as despite of carrying out pre-splitting; the benches experienced back breaks adversely affecting the stability of the remaining walls. Normal production blast consists of detonation of 6–8 rows involving 140–200 holes in a blast round. A master plan of the pre-split holes position at spacing of 1.2m was prepared. The available explosive was in the cartridge diameter of 25mm which provided decoupling ratio of 1:3.6. Each bench of footwall and of all stages of hang wall is pre-splitted to minimize damage to the rock mass. Pre-split holes of about 700,000m are being drilled annually to get desired pit slopes. In the experimental trials the mouths of the pre-split holes were left without explosives from 0.8 to 2.7m. In the latter stage the inclined holes of 115mm at 80°, 70° and 60° were experimented. The pre-split holes drilled at 1.2m spacing with 60° inclination on footwall and 70° on hangwall yielded desired results.

Coupling of two methods, waveform superposition and numerical, to model blast vibration effect on slope stability in jointed rock masses

Drilling and blasting is a major technology in mining since it is necessary for the initial breakage of rock masses in mining. Only a fraction of the explosive energy is efficiently consumed in the actual breakage and displacement of the rock mass, and the rest of the energy is spent in undesirable effects, such as ground vibrations. The prediction of induced ground vibrations across a fractured rock mass is of great concern to rock engineers in assessing the stability of rock slopes in open pit mines. The waveform superposition method was used in the Gol-E-Gohar iron mine to simulate the production blast seismograms based upon the single-hole shot vibration measurements carried out at a distance of 39m from the blast. The simulated production blast seismograms were then used as input to predict particle velocity time histories of blast vibrations in the mine wall using the universal distinct element code (UDEC). Simulated time histories of particle velocity showed a good agreement with the measured production blast time histories. Displacements and peak particle velocities were determined at various points of the engineered slope. The maximum displacement at the crest of the nearest bench in the X and Y directions was 26mm, which is acceptable in regard to open pit slope stability.

Numerical modeling of presplitting controlled method in continuum rock masses

Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. The less competent the rock mass itself, the more care has to be taken in avoiding damage. Presplitting is one of the most common methods which is used in many open pit minings and surface blast designs. The purpose of presplitting is to form a fracture plane across which the radial cracks from the production blast cannot travel. Presplitting should be thought of as a protective measure to keep the final wall from being damaged by the production blasting. The purpose of this study is to investigate the effect of presplitting on generation of a smooth wall in a rock domain under blast process in continuum rock mess. The 2D distinct element code was used to simulate the presplitting in a rock slope (open pit mining). The blast load history was applied as a function of time to inner wall of each blasthole. Important parameters that were considered in the analysis were stress tensor and fracturing pattern. The blast loading magnitude and blasthole spacing were found to be very significant in the final results.

Research on Influence of Loose Coverage Rock Fragment Distribution

The sublevel caving mining method is widely applied in China's underground mines, in particular of iron mines. Its mining work is under the protection of loose coverage rock. The loose coverage rock is located in the stope for a long time, and its frequently squeezed from production blasting, impact effect and the colliding and breaking in the falling process, it comes into being a large number of powder and small pieces of rocks. The rock powder and small fragments have such characteristics-good mobility and strong permeability. With the increasement of mining depth, the rock powder and small fragments in the loose coverage rock will be earlier to reach the ores than the big fragments of the same level. As a result, ore dilution will prematurely appear. To better know the phenomenon, this paper explores ore dilution of different fragment distribution of loose coverage rock by physical simulation experimental method. The research results have certain guiding significance for the actual production of underground mines.

A rock engineering systems based model to predict rock fragmentation by blasting

A new model for prediction of rock fragmentation by blasting is presented based upon the basic concepts of rock engineering systems (RES). The newly proposed approach involves 16 effective parameters on fragmentation by blasting with keeping simplicity as well. The data for 30 blasts, carried out at Sungun copper mine, western Iran, were used to predict fragmentation by the RES based model as well as Kuz–Ram and multiple regression modeling. To validate the new model, the fragmentations of nine production blasts were measured and the results obtained were compared with the predictions carried out by the RES, Kuz–Ram and multiple regression models. Coefficient of determination (R2) and root mean square error (RMSE) were calculated for the models to compare the results obtained. For the RES, linear, polynomial, power, logarithmic, exponential and Kuz–Ram models, R2 and RSME are equal to (0.65 and 14.51), (0.58 and 29.73), (0.54 and 21.58), (0.60 and 32.64), (0.61 and 23.80), (0.50 and 184.60) and (0.46 and 22.22) respectively. These indicate that the RES based model predictor with higher R2 and less RMSE performs better than the other models.

A coupled method to study blast wave propagation in fractured rock masses and estimate unknown properties

The prediction of blast-induced ground vibrations across fractured rock masses is of great concern to rock engineers in evaluating the stability of rock slopes in open pit mines. Hence, many researchers have studied the wave propagation through rock slopes and tried to simulate its complexities using different methods. At the present work, the ‘linear superposition method’ was used at the Gol-e-Gohar iron ore mine to simulate the production blast seismograms based upon measurements of single-hole shot vibrations, carried out at a distance of 39m from the blast. The production blast seismograms were then used as the input to predict particle velocity time histories in the mine wall using the three-dimensional discrete element method. By back analysis of measured blast waveforms at a distance of approximately 300m away, mechanical properties of in-filled faults of the study area were determined. In combination with the numerical model, a ‘simulated annealing’ search algorithm was employed to find the optimum values of unknown parameters. The final results of time histories of particle velocity show a good agreement with the measured time histories.

Moment tensor inversion of waveforms: a two-step time-frequency approach

SUMMARY We present a moment tensor inversion of waveforms, which is more robust and yields more stable and more accurate results than standard approaches. The inversion is performed in two steps and combines inversions in time and frequency domains. First, the inversion for the source-time function is performed in the frequency domain using complex spectra. Second, the time-domain inversion for the moment tensor is performed using the source-time function calculated in the first step. In this way, we can consider a realistic, complex source-time function and still keep the final moment tensor inversion linear. Using numerical modelling, we compare the efficiency and accuracy of the proposed approach with standard waveform inversions. We study the sensitivity of the retrieved double-couple and non-double-couple components of the moment tensors to noise in the data, to inaccuracies of the location and of the velocity model, and to the type of the focal mechanism. Finally, the proposed moment tensor inversion is tested on real data observed in a complex 3-D inhomogeneous geological environment: a production blast and a rockburst in the Pyhasalmi ore mine, Finland.

Burden prediction in blasting operation using rock geomechanical properties

Burden prediction is a vital task in the production blasting. Both the excessive and insufficient burden can significantly affect the result of blasting operation. The burden which is determined by empirical models is often inaccurate and needs to be adjusted experimentally. In this paper, an attempt was made to develop an artificial neural network (ANN) in order to predict burden in the blasting operation of the Mouteh gold mine, using considering geomechanical properties of rocks as input parameters. As such here, network inputs consist of blastability index (BI), rock quality designation (RQD), unconfined compressive strength (UCS), density, and cohesive strength. To make a database (including 95 datasets), rock samples are used from Iran’s Mouteh goldmine. Trying various types of the networks, a neural network, with architecture 5-15-10-1, was found to be optimum. Superiority of ANN over regression model is proved by calculating. To compare the performance of the ANN modeling with that of multivariable regression analysis (MVRA), mean absolute error (Ea), mean relative error (Er), and determination coefficient (R2) between predicted and real values were calculated for both the models. It was observed that the ANN prediction capability is better than that of MVRA. The absolute and relative errors for the ANN model were calculated 0.05 m and 3.85%, respectively, whereas for the regression analysis, these errors were computed 0.11 m and 5.63%, respectively. Moreover, determination coefficient of the ANN model and MVRA were determined 0.987 and 0.924, respectively. Further, a sensitivity analysis shows that while BI and RQD were recognized as the most sensitive and effective parameters, cohesive strength is considered as the least sensitive input parameters on the ANN model output effective on the proposed (burden).

Multiple Seed Waveform (MSW) vibration model and some case studies

Most existing blast vibration models are designed for far-field vibration using a single seed wave to represent each blasthole within a blast for a point of interest and do not simulate wave shape change over the distance. Without modelling the waveform change, such models cannot reliably predict the amplitude and frequency of the blast vibration from a production blast. A multiple-seed blast vibration model (MSW) developed within Orica in recent years is suitable for near and far-field blast vibration. With the recent development, it is also applicable for open pit and underground blast vibrations including tunnel blasting. This paper updates the current capabilities of the MSW model with selected case studies.

Prediction of near field overpressure from quarry blasting

This paper investigates the propagation of airblast or pressure waves in air produced by bench blasting (i.e. detonation of the explosive in a row of blastholes, breaking the burden of rock towards the free vertical face of the block). Peak overpressure is calculated as a function of blasting parameters (explosive mass per delay and velocity at which the detonation sequence proceeds along the bench) and the polar coordinates of the position of interest (distance to the source and azimuth with respect to the free face). The model has been fitted to empirical data using linear least squares. The data set is composed of 122 airblast records monitored at distances less than 400 m in 41 production blasts carried out in two quarries. The model is statistically significant and has a determination coefficient of 0.87. The formula is validated from 12 airblast measurements gathered in five additional blasts.

On the prediction of mucking rates in metal ore blasting

A model for the calculation of the productivity of cyclic excavators is developed. The production rate results as a product of an ideal, maximum, productivity rate (one of the coefficients of the model) times an operating efficiency. The latter is described as a function of three variables (rock strength, nominal bucket capacity and explosive energy concentration) and three more coefficients. The coefficients of the model have been obtained from field measurements in twenty production blasts at two open pit mines, for which mechanical properties of the rock, blasting characteristics and mucking rates were carefully measured. The model is statistically significant and explains up to 90 % of the variance of the production rate measurements.

Prediction of Rock Fragmentation Due to Blasting in Sarcheshmeh Copper Mine Using Artificial Neural Networks

The main objective in production blasting is to achieve a proper fragmentation. In this paper, rock fragmentation the Sarcheshmeh copper mine has been predicted by developing a model using artificial neural network. To construct the model, parameters such as burden to spacing ratio, hole-diameter, stemming, total charge-per-delay and point load index have been considered as input parameters. A model with architecture 9-8-5-1 trained by back propagation method was found to be optimum. To compare performance of the neural network, statistical method was also applied. Determination coefficient (R2) and root mean square error were calculated for both the models, which show absolute superiority of neural network over traditional statistical method.

Characterisation of blast vibration generated from open-pit blasting at surface and in belowground openings

The safety and stability of underground coal mine workings may be affected by opencast mines operating in close proximity. A study was conducted to investigate the level of vibration generated from opencast blasting in the nearby underground coal mine openings and at a similar distance at the surface. Eight production blasts were performed and nineteen blast vibration data sets were recorded on the surface behind the opencast blasting face and also in underground openings at similar distances. It was observed that the magnitude of vibration recorded on the surface was higher than those recorded in underground openings. The findings of the study are of importance for the assessment of safety and stability of unapproachable belowground installations affected by the vibration produced due to opencast blasting.

Critical Investigation into the Drilling and Blasting Work done at the "Mormont" Quarry in Order to Reduce Blast Vibrations

Holcim Eclepens produces about 650,000 tons of cement per year. To supply the plant with sufficient raw material in 2005 about 670,000 tons of limestone were extracted at the "Mormont" quarry by drilling and blasting. About 200,000 t were mined at the "Marniere" marl quarry by using an excavator. Since many years Eclepens, a village nearby the "Mormont" quarry, has been complaining about ongoing blast vibrations. Therefore, Holcim guaranteed to keep the future blast vibrations below 3 mm/s, which was distinctly below the legal limit. In 2005 Holcim decided to increase the raw material extraction by 30 %. As the people of Eclepens feared an increase of blast vibrations, too Holcim set up the working pro-gram "concept carriere 2005" to analyze critically the future impact of that extraction increase. Today, after more than 160 production blasts, only three single blasts exceeded the 3 mm/s limit. The majority of the blast vibrations are distinctly below 2 mm/s.

Shotcrete on rock exposed to large-scale blasting

Shotcrete sprayed on rock is vulnerable to stress waves from large-scale blasting in tunnels and mines. Shotcrete support in a Swedish underground mine is studied through numerical analysis and comparisons with previous results, measurements and observations in situ. A previously developed finite-element model that consists of beam and spring elements is used to calculate the response of shotcrete to vibrations from production blasts in the mine. The modelling approach is similar to that of a building during an earthquake, with accelerations measured in situ used as loads. The analysis shows that the calculated bond stresses exceed the strength in the interface between shotcrete and rock close to the blasts. The results show that it is possible to optimise the scheme of the blasting so that shotcrete is protected from damaging vibrations. Also recommended, for practical use, are minimum distances to large amounts of explosives given. This set of recommendations is a supplement to previously given guidelines valid for small amounts of explosives at short distances from shotcrete on rock.

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; Lopez 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.

Influence of initiation mode of explosives in opencast blasting on ground vibration

The measurement and analysis of blast induced vibration is presently more state of the art than ever before. A modern understanding of the basic concepts behind vibration effects can help a beleaguered end user more confident about what their measurement really mean. It is reported that blast conducted with non-electric initiation system enhanced the efficiencies of Heavy Earth Moving Machinery (HEMM) machineries and reduced the reported nuisance of blasting. The developed countries are adopting the third generation of electronic detonators but in India the use of detonating fuse for blast initiation is still in practice. There are number of reasons stated by mine officials for this practice being still followed by mining industry. The one of the important reasons is the price ratio of Nonel tubes and detonating cords/fuse, which is comparatively very high in India in comparison with the other countries. A study was planned to investigate the influence of direction of initiation in the blasthole on ground vibration. The four opencast coal mines were selected for the study purpose. The two blasts at same bench were conducted while keeping all the blast design and explosives parameters such as, burden, spacing, hole depth, hole diameter, charge per hole, charge per delay, total charge in blast round, etc., identical. The explosive make for a set of two blasts were of same manufacture and both the blasts were conducted on same day to avoid the variation in explosive formulation. Blast induced vibrations were monitored at 6–11 locations. The experimental set of blasts includes single hole blasts, production blasts, as well as dragline blasts, performed by only changing mode of initiation, i.e. initiation of booster with detonating cord and with non-electric initiation in the bottom of the hole at floor level while maintaining all other parameters identical. The result indicated that former generated lower vibration levels compared with previous mode of initiation. The reductions in vibrations were observed up to 36·2% by for blastholes of depth >20 m. The minimum reduction of vibration was 8·2% for shorter blastholes depth of 7·5 m.