Production Blasts Research Articles

Estimation of Jones-Wilkins-Lee parameters of emulsion explosives using cylinder tests and their numerical validation

A microspheres-sensitized emulsion explosive, to be used in rock blasting tests, is characterized by means of the cylinder test. This test measures the expansion of a copper tube upon detonation of an explosive charge inside. Eight cylinder tests have been made with two different diameters (50 mm and 100 mm) and two different densities (1180 kg/m3 and 1030 kg/m3) in a 2 × 2 × 2 test matrix. The expansion energy is affected by the density but not by the test diameter, which suggests that this explosive, at the densities studied, behaves close to ideal already at 50 mm. The explosive velocity of detonation had been also measured within the trials. In addition, velocities of detonation were measured in six production blasts and reported here. The Jones–Wilkins–Lee (JWL) equation of state parameters have been obtained for this emulsion at the densities and diameters tested. The calculation method includes a radial expansion function, with a non-zero initial velocity at the onset of the expansion. The equations reflecting the CJ state conditions and the measured expansion energy were solved for the JWL parameters by a non-linear least squares scheme. These parameters have been validated with three different LS-DYNA models (Lagrangian-Lagrangian, Smooth Particle Hydrodynamic-Lagrangian, Arbitrary Lagrangian Eulerian-Lagrangian). All models show a good correlation with the test results when comparing them against the detonation pressure, the cylinder wall expansion, the Gurney limit velocities and the radial wall velocities. The Smooth Particle Hydrodynamic is the best numerical model for replicating the detonation pressure, the Lagrangian for the cylinder wall expansion radius and velocity history, and Arbitrary Lagrangian Eulerian on the overall performance. Arbitrary Lagrangian Eulerian and Smooth Particle Hydrodynamic techniques are widely used to describe the materials subjected to large deformations, such as explosives, on full-scale simulations for civil and mining applications. The good agreement between numerical and experimental results justifies the use of these methods to model the expansion of detonation products.

Modified scaled distance regression analysis approach for prediction of blast-induced ground vibration in multi-hole blasting

The blast-induced ground vibration prediction using scaled distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with scaled distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using scaled distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%.

Degradation of a discrete infilled joint shear strength subjected to repeated blast-induced vibrations

This paper presents the results of a series of numerical modeling experiments aimed at quantifying blast-induced degradation of shear strength of discontinuities. Near-field vibration history of a single-row production blast in a limestone quarry was used as input to the numerical model. For this purpose, two rock blocks, representing a stiff massive sulfide rock and a weaker limestone rock, were simulated using the 2D Particle Flow Code (PFC2D). Rock mass containing a single inclined joint was modeled as Mohr-Coulomb. The results show that the crack generation rate is increased in both samples after repetitive vibration loading. Joint shear strength degradation rate in the stiffer massive sulfide rock sample is higher than the softer limestone rock, which is attributed to the higher seismic impedance mismatch. The results show that even low-amplitude blasting vibrations (<80 mm/s), when repeated as in multi-hole blasts, can significantly degrade joint shear strength in the nearby pit walls.

Tectonic fault monitoring at open pit mine at Zarnitsa Kimberlite Pipe

The article describes application of Karier instrumentation designed at the Institute of Mining to study fracture formation in rocks. The instrumentation composed of three sensors was used to control widening of a tectonic fault intersecting an open pit mine at Zarnitsa Kimberlite Pipe in Yakutia. The monitoring between 28 November and 28 December in 2016 recorded convergence of the fault walls from one side of the open pit mine and widening from the other side. After production blasts, the fault first grows in width and then recovers.

A New Mathematical Model for Predicting the Surface Vibration Velocity on the Step Topography

In order to control production blasting and optimize mining operation, it is important to study the step topography vibration amplification and attenuation effect in the open‐pit mine. Surface particle vibration velocity attenuation characteristics, the formation, and change rules of the terrain effect were studied by analyzing the field measured data. Results show that local amplification effect and local attenuation amplification effect of particle vibration velocity are obvious. Amplification effect associates with bench height, and the attenuation effect is closely related with the distance from the vibration source and distance from the top. With the increase of elevation, vibration magnification of the particle on the top was 1.1∼1.4. Because of the influence of the terrain effect, particle vibration velocity on the slope toe was obviously inhibitory. Based on the measured data, elevation amplification factor and clamping effect factor which influence blasting vibration velocity are put forward, and a new mathematical model considering the attenuation coefficient, the elevation amplification coefficient, and the clamping effect coefficient for predicting the blasting vibration velocity of the step topography is further improved. The regression analysis results show that the fitting coefficient of determination of the new prediction model is 0.8152 in horizontal and 0.8902 in vertical, respectively, and the prediction error is less than 20%, which is much better than other formulas. This new model provides effective reference for blasting seismic wave propagation law research of slope engineering.

Mineralogy identification through linear unmixing of blast hole geochemistry

ABSTRACTValidating and updating geological models is important in mining to reduce the errors between the predicted and mined values. In the Banded Iron Formation-hosted iron ore deposits in the Hamersley Ranges Western Australia, geological models are based on widely spaced exploration data, resulting in errors on smaller scales. Closely spaced chemical assays from production blast hole drilling become available for updating models, but do not routinely provide mineralogy. This study identifies mineralogy by applying linear unmixing methods to chemical assays. Linear spectral mixture analysis (LSMA), extended linear mixing model (ELMM) and spectral unmixing within a multi-task GP framework (SUGP) successfully identified the mineralogy in synthetic mixtures, with RMSEs of 13.75%, 11.78% and 11.97%. LSMA had consistently poorer results. SUGP was more accurate when using fewer endmember examples. ELMM was easier to train and required less processing power. Therefore either SUGP or ELMM should be chosen to identify the mineralogy depending on the application.

Numerical modelling approach for mine backfill

Numerical modelling is broadly used for assessing complex scenarios in underground mines, including mining sequence and blast-induced vibrations from production blasting. Sublevel stoping mining methods with delayed backfill are extensively used to exploit steeply dipping ore bodies by Canadian hard-rock metal mines. Mine backfill is an important constituent of mining process. Numerical modelling of mine backfill material needs special attention as the numerical model must behave realistically and in accordance with the site conditions. This paper discusses a numerical modelling strategy for modelling mine backfill material. The modelling strategy is studied using a case study mine from Canadian mining industry. In the end, results of numerical model parametric study are shown and discussed.

Preparation and conduction of a production blast at an intersection in Kirov Mine, Apatit

Preparation and conduction of a production blast at an intersection in Kirov Mine, Apatit

Evaluating orthotropic continuum analysis of stress wave propagation through a jointed rock mass

Continuum modeling and discontinuum modeling are two approaches that are used to study the problem of stress wave propagation in jointed rock masses. In this study, a numerical analysis of blast wave propagation through a rock mass of three orthogonal joint sets was conducted by replacing the discontinuous media with orthotropic continua. The features of the simulated blast waveforms were fitted to those of the real seismograms (recorded at a distance of 300 m from a production blast at the Gol-e-Gohar iron ore mine) by iterative adjustment of the variable parameters. In order to account for the effect of rock joint dilation using the orthotropic elastic constitutive model, a search range was considered for the nonzero off-diagonal terms of the compliance matrix of the equivalent media, within which these three parameters were back-calculated independently. A simulated annealing search algorithm was used in conjunction with the numerical modeling to supervise the parameter adjustment. Finally, the response of the equivalent continuous model to dynamic loading was compared with the in situ records and the response observed in previously performed discrete modeling. The results demonstrated that the values of the peak particle velocities and the predominant frequencies in the model and those from site monitoring were in good accord. However, eliminating joints led to wider response Fourier spectra than seen for the real records and the jointed model results, and the numerical model required increased additional damping to compensate for this simplification.

Modelling the Source of Blasting for the Numerical Simulation of Blast-Induced Ground Vibrations: A Review

The mining and construction industries have long been faced with considerable attention and criticism in regard to the effects of blasting. The generation of ground vibrations is one of the most significant factors associated with blasting and is becoming increasingly important as mining sites are now regularly located near urban areas. This is of concern to not only the operators of the mine but also residents. Mining sites are subjected to an inevitable compromise: a production blast is designed to fragment the utmost amount of rock possible; however, any increase in the blast can generate ground vibrations which can propagate great distances and cause structural damage or discomfort to residents in surrounding urban areas. To accurately predict the propagation of ground vibrations near these sensitive areas, the blasting process and surrounding environment must be characterised and understood. As an initial step, an accurate model of the source of blast-induced vibrations is required. This paper presents a comprehensive review of the approaches to model the blasting source in order to critically evaluate developments in the field. An overview of the blasting process and description of the various factors which influence the blast performance and subsequent ground vibrations are also presented. Several approaches to analytically model explosives are discussed. Ground vibration prediction methods focused on seed waveform and charge weight scaling techniques are presented. Finally, numerical simulations of the blasting source are discussed, including methods to estimate blasthole wall pressure time-history, and hydrodynamic codes.

Evaluating pre-split performance through direct measurements of near field acceleration, particle velocity and gas pressure

Pre-split techniques are routinely used to minimise rock mass damage from production blasting. Design parameters rely on site-specific guidelines and in order to improve designs, it is important to be able to measure its performance. One criterion is related to the pre-split ability to adequately filter blast-induced stresses and explosion gases. This paper presents the results of a monitoring program implemented to evaluate the performance of pre-split practices. Triaxial accelerometers and pressure sensors were installed behind pre-split lines and a site-specific criterion was established to determine whether or not filtering effects were occurring. The recorded maximum peak particle velocity (PPV) vector sum behind pre-splits in all blasts monitored was below the threshold of damage of intact rock and rock mass discontinuities. With regards to the recorded gas pressure, measurements from production blasts showed fluctuations of low pressure levels, indicating that pre-split parameters were effectively filtering-induced stresses and gases.

Evidences of the influence of the detonation sequence in rock fragmentation by blasting – Part I

Drilling and blasting are fundamental operations in the mining cycle and consti tute an important component of the mining costs. Rock fragmentation can in principle be managed by means of two options: by increasing or reducing the specific consumption of explosives, or by modifying the drilling pattern. The choice of one or other type of control depends on the relationship between the unit costs of drilling and explosives, and on technical restrictions or regulations imposed by different reasons. It is then necessary to identify the link between the blast design and some factors affecting the downstream processing of the product. This paper analyzes the theoretical basis aimed at evaluating the main parameters involved when organizing a production blast in open pit quarries. In particular, a method developed through the analysis of the results in a large number of limestone open pit quarries in Italy is described and commented. The first experimental results in Brazil have been obtained by applying this method at the Experimental Mine of the Research Center of Responsible Mining of the University of Sao Paulo. Experimental methods and results will be analyzed and discussed in the second part of this paper.

BLAST VIBRATION MODELING USING LINEAR SUPERPOSITION METHOD

A linear superposition method was used for modeling the time history of the production blast vibrations and optimizing the blast sequence to reduce vibration levels in Sar-Cheshmeh copper mine, Kerman, Iran. A single-hole blast for modeling and two double-hole blasts with time delays of 25 and 65 ms between two holes for modeling validation were carried out. The generated vibrations were measured at seven points with different distances and directions around the blasts. These records contain information about the complex mechanism of seismic energy radiation from an explosive source as well as the filtering effect of the signal travel path. Totally, 40 seismograms were synthesized (3 components for each point) for two blasts using the linear superposition method. The results obtained presented a good correlation between the synthetic and measured seismograms. Also, a comparison was made between the measured peak particle velocities (PPVs) and those obtained from the scaled-distance method and linear superposition modeling. This shows the merits of linear superposition modeling to predict PPVs. Moreover, the recorded seismograms of the single-hole blast were used to simulate the vibrations produced by a production blast at seven points. Furthermore, by using a systematic variation of firing delay in the modeling procedure, the effect of delay on the production blast vibrations was studied. The production blast simulations showed that for Sar-Cheshmeh copper mine, the blasts carried out with the inter-row delays more than 40 ms can significantly reduce vibration levels.

Evaluating Ground Improvement after Blast Densification: Performance at the Oakridge Landfill

AbstractBlasting has long been used as a ground improvement technique to densify loose granular soils. Explosives detonated at depth induce liquefaction in the target sand followed by pore pressure dissipation and attendant consolidation. Improvement typically is verified via measured surface settlements and increased penetration resistance with in situ tests such as the cone penetration test (CPT). However, an increase in penetration resistance is often not observed for months or even years after blasting. The results of instrumentation at a production blast zone at the Oakridge Landfill are reported herein. Instrumentation included surface settlements, pore pressure measurements inside and outside the blast zone, preblast and postblast piezocone (CPTu) soundings, and gas concentrations of pore fluid. No increase in penetration resistance with the CPTu was detected 53 days after the final blast, despite more than 0.5 m of settlement and an increase in relative density to 80% or more in some areas. Result...

Seismic data classification using cluster analysis for predicting ground vibration caused by blast

Ground vibration around mining areas is one of the undesirable phenomena of production blasts. To predict vibration magnitude due to production blasts in Sarcheshmeh Copper Mine, the seismic wave characteristics are recorded in two parts of south-east and south-west mine by seismometers. The blasts of each part are grouped by cluster analysis, and using multivariate analysis for each of the groups, models were defined to predict peak particle velocity (PPV). For model validation, first PPV values of some recorded experimental blast in the mine was predicated and the root mean squared error (RMSE) and mean absolute error were calculated for the cases of after- and before-grouped seismic data. In the south-west region of the mine, the RMSE is calculated after and before clustering the data 8.9 and 11.95, respectively. These values are shown; the created models after clustering in comparison with before clustering could decrease the rate of error up to 3. This rate of error and the value of mean absolute error are shown; the performance of created models is improved after the cluster analysis predicated the PPV. But in the south-east region of the mine, the value of RMSE by means of created models after clustering the data is increased in comparison with before clustering up to 0.22. This shows that the performance of models after clustering is decreased.

Dynamic Modelling of Fault Slip Induced by Stress Waves due to Stope Production Blasts

Seismic events can take place due to the interaction of stress waves induced by stope production blasts with faults located in close proximity to stopes. The occurrence of such seismic events needs to be controlled to ensure the safety of the mine operators and the underground mine workings. This paper presents the results of a dynamic numerical modelling study of fault slip induced by stress waves resulting from stope production blasts. First, the calibration of a numerical model having a single blast hole is performed using a charge weight scaling law to determine blast pressure and damping coefficient of the rockmass. Subsequently, a numerical model of a typical Canadian metal mine encompassing a fault parallel to a tabular ore deposit is constructed, and the simulation of stope extraction sequence is carried out with static analyses until the fault exhibits slip burst conditions. At that point, the dynamic analysis begins by applying the calibrated blast pressure to the stope wall in the form of velocities generated by the blast holes. It is shown from the results obtained from the dynamic analysis that the stress waves reflected on the fault create a drop of normal stresses acting on the fault, which produces a reduction in shear stresses while resulting in fault slip. The influence of blast sequences on the behaviour of the fault is also examined assuming several types of blast sequences. Comparison of the blast sequence simulation results indicates that performing simultaneous blasts symmetrically induces the same level of seismic events as separate blasts, although seismic energy is more rapidly released when blasts are performed symmetrically. On the other hand when nine blast holes are blasted simultaneously, a large seismic event is induced, compared to the other two blasts. It is concluded that the separate blasts might be employed under the adopted geological conditions. The developed methodology and procedure to arrive at an ideal blast sequence can be applied to other mines where faults are found in the vicinity of stopes.

Design of controlled blasting (pre-splitting) in Golegohar iron ore mine, Iran

Pre-splitting is a controlled blasting technique with applications in open pit mines. The main objectives of pre-splitting in open pit mining are: preventing/controlling back-break; controlling excessive ground vibrations; and filtering the effects of explosive gases from production blasting. This technique is especially effective in back-break control through providing a separating surface between the main blasting pattern and open pit final walls. In this study, a large open pit mine was the case study for the goal of designing pre-splitting through implementation of direct and cost effective experiments. Three tests were designed and performed at the mine. Back-break was successfully controlled through proper design of pre-splitting based on the results of the experiments.

Blast furnace stockline measurement using radar

This paper presents a synergistic approach to stockline depth tracking within a blast furnace. Frequency modulated continuous wave (FMCW) radar can be used to measure the depth and surface profile of the burden surface; however, the radar signal is easily disturbed by radar anomalies during the process of continuous measurement. Data from the rotating chute and the charging signal provide information on the contextual relevance of these anomalies. An improved Kalman filter and anomaly detection model were developed to increase measurement accuracy by utilising contextual information. The approach was validated on production blast furnaces. The root mean squared (RMS) error in the measured depth was reduced by 17% when the proposed approach is used. The results suggest that this approach successfully adapts to changes in the pattern and characteristics of the burden surface.

Numerical simulation of rock mass vibrations induced by nearby production blast

It is of importance to understand the effect of production blasts on the surrounding rock formations in underground mines. This study presents a numerical procedure to simulate stress waves resulting from nearby production blasts. First, the damping coefficient and peak borehole pressure are calibrated using a dynamic numerical model of a single blast hole. The resulting time-varying particle velocities in the surrounding rock mass at the specified points are calculated. These are then used as input parameters in a three-dimensional mine-wide model, considering a positional relationship between the blast hole and the specified points on the wall rock. The mine-wide model encompasses a fault running parallel to a steeply dipping, tabular ore deposit. Dynamic analysis simulating the effect of production blasts is conducted after the extraction of mining blocks with static analysis. In this study, variations of stresses along the fault due to blast-induced stress waves are examined. Results demonstrate that the developed methodology can reasonably simulate stress changes induced by stress waves on the fault. The methodology considers blast sequences and time-varying blast loads that vary according to the positional relationship between the blast holes and the specified points on the wall rock.

Distinct element modelling of fracture plan control in continuum and jointed rock mass in presplitting method of surface mining

Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. Presplitting is one of the most common methods which is used in many open pit mining and surface blast design. The purpose of presplitting is to form a fracture plane across which the radial cracks from the production blast cannot travel. The purpose of this study is to investigate of effect of presplitting on the generation of a smooth wall in continuum and jointed rock mass. The 2D distinct element code was used to simulate the presplitting in a rock slope. The blast load history as a function of time was applied to the 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 and jointing pattern were found to be very significant in the final results.