Studies on the Effect of Burden on Blast Damage and the Implementation of New Blasting Practices to Improve Productivity at KCGMs Fimiston Mine

Wall control blasting practices arc necessary to reduce the impact of blasting on mine faces but can also have a significant negative impact on mine productivity and operating costs. The conventional practice in deep open pit mines is to use so-called trim blasts adjacent to pit walls. To provide burden relief these trim blasts have fewer rows than full production blasts and are fired to a cleared free-face: hence they are termed 'unchoked.' This practice leads to scheduling constraints on the pit operations and can cause ore dilution due to excessive muckpile movement. The use of such trim blasts stems from the perception that increased wall damage results from 'choked' blasts. These concerns are based on the unproven assumptions that blast vibration levels and explosive gas penetration increase with increased blast burden and face confinement. This paper describes work undertaken as part of a major investigation into wall control blasting at the KCGM Fimiston Mine, Kalgoorlie, Western Australia. It details a study to assess damage effects due to blast burden. Borehole air pressure measurements and borehole video camera inspections owere done behind a series of single blastholes drilled owith varying burden distances, as owell as behind a dedicated trim blast and a full production blast. It was found that the measured damage effects, including visible rock cracking, dilation, and the limited extent of gas penetration behind the blastholes, did not vary significantly with burden or blast type for the cases tested. This result was in complete agreement with detailed vibration measurements conducted by Blair and Armstrong [1] during the study, which found that vibration was independent of blast burden. As a result of these investigations, changes to the blasting practices at the mine were implemented. Dedicated trim blasts and free-face blasting have been replaced by modified production blasts and the practice of 'choking' blasts has been introduced. This has resulted in a significant improvement in productivity and cost savings without compromising pit wall integrity.     

A Feasibility Study on Controlling Ground Vibrations Caused by Blasts in Malmberget Underground Mine

In order to control or reduce the ground vibrations caused by underground blasts in Malmberget mine, a number of blast tests were carried out during production blasts and a series of single shot waveforms were obtained. Then the single shot waveforms from the same ring or different rings were analysed and compared with each other. The results showed that the single shots are reproducible, meaning that the ground vibrations caused by underground blasts can be controlled by means of the interference of the vibration waveforms measured. Finally, a formal test using electronic detonators and employing an optimum delay time of 8 ms was done in production. The test for an 11-borehole ring shows that the maximum vertical ground vibrations are reduced to the maximum vertical vibrations of a single shot. Particularly, the total vibration history for the 11-borehole-ring blast is shortened to about 200 ms over a velocity of 2 mm/s. However, the total vibration history of a normal production blast of 11-borehole ring is always 1400 ms over a velocity of 2 mm/s, namely the total vibration time of a production blast can be reduced to one seventh of that of the common production blasts by using the vibration control method. This indicates that the vibration control method introduced in the paper is feasible for underground mining blasts.     

Micro-sequential contour blasting—how does it influence the surrounding rock mass?

The optimal delay time between the contour holes in rock blasting has been studied by theoretical and empirical research in Sweden, regarding ground vibrations, increase in crack frequency, radial crack length and finally overbreak (half cast factor). The model test presented in this paper concerns controlled contour blasting in tunnelling and the full-scale blasts concern tunnelling, road cutting, and dimensional stone quarrying. The results indicate that the microsequential contour blasting technique (contour holes fired in sequence and with a delay in the order of 1–2 ms) is superior to simultaneous initiation both regarding blast-induced ground vibrations and crack frequency increase in the rock mass. Both these evaluation methods reflects the conditions deeper in the remaining rock mass. Simultaneous initiation, however, is superior to micro-sequential contour blasting both regarding the half cast factor and the length of radial cracks emanating from the blastholes. These two parameters are more related to the surface conditions after blasting. The industrial applications of this new knowledge are the use of micro-sequential contour blasting when ground vibrations are of greater concern than the contour, for example, in trench blasting or quarrying in urban areas, and the use of simultaneous initiation when an even rock surface is of high priority.     

Application of an Expert System for the Assessment of Blast Vibration

The purpose of this article is to evaluate and predict the blast induced ground vibration using different conventional vibration predictors and artificial neural network (ANN) at a surface coal mine of India. Ground Vibration is a seismic wave that spread out from the blast hole when detonated in a confined manner. 128 blast vibrations were recorded and monitored in and around the surface coal mine at different strategic and vulnerable locations. Among these, 103 blast vibrations data sets were used for the training of the ANN network as well as to determine site constants of various conventional vibration predictors, whereas rest 25 blast vibration data sets were used for the validation and comparison by ANN and empirical formulas. Two types of ANN model based on two parameters (maximum charge per delay and distance between blast face to monitoring point) and multiple parameters (burden, spacing, charge length, maximum charge per delay and distance between blast face to monitoring point) were used in the present study to predict the peak particle velocity. Finally, it is found that the ANN model based on multiple input parameters have better prediction capability over two input parameters ANN model and conventional vibration predictors.     

Response of Concrete and Masonry Dams to Ground Vibration due to Blasting

The safety and stability of concrete and masonry dams is a great concern when blasting has to be conducted close to these dams in order to construct small hydro-electric projects. There is a danger of ground vibration amplification to those residential-type buildings that are built close to these dams.

Responses of three concrete and masonry dams were measured directly by conducting a number of blasts and by monitoring vibration in the ground as well as on the dams. The amplitudes and frequencies of the motions were analysed and vibration attenuation relations were derived. These relations were used to compare the vibration levels on the dams with those in the ground.

Because of close-in construction blasts that produced high frequency ground vibrations, there was no amplification of the ground vibrations by these dams. The measured amplitudes of ground vibration were comparable to those of the dams.     

Studies on Flyrock at Limestone Quarries

Summary Observed flyrock distances for 47 blasts at six limestone quarries along with blast design parameters are presented. The influence of blasthole diameter, burden, stemming length, powder factor, the condition of blastholes (dry or wet) and the initiation systems on generation of flyrock is analysed and the most critical parameters for flyrock control are identified. Based on the analysis of results, suggestions are given to minimise the flyrock hazards at limestone quarries.     

Reducing ground vibrations caused by underground blasts in LKAB Malmberget mine

Due to the large-scale sub-level caving in Malmberget mine and the short distance between the mine and Malmberget town, the ground vibrations in the town have reached a high level since the year 2001 when large scale caving mining started. In order to control and reduce the high vibrations, LKAB launched a research project on active reduction of vibrations in Malmberget by using the wave interference or wave superposition method with electronic detonators. By means of this method, the vertical vibrations were reduced by 10% and the total vibration time for a ring blast was reduced by 80% according to five ring tests in the mine. For a further reduction of the vibrations, a second method, named changing initiation sequence in ring blasts, was developed on the basis of stress wave theory and the geographic conditions of the town and the mine. The second method has so far been applied in all of the drifts near the town, and the vibrations measured at the town show that the vertical vibrations caused by production blasts in the mine have been reduced by more than 31% on average. In addition, a third method, dividing a ring into two parts during blasting, was developed and used to reduce the ground vibrations from a number of very large rings in the mine. The results indicate that the vibrations have been reduced by more than 33%, and a more interesting and surprising result is that ore extraction has been increased by the third method.     

An assessment of environmental impacts of quarry-blasting operation: a case study in Istanbul, Turkey

This study evaluates the impacts resulting from quarry-blasting operation on nearby buildings and structures as it generates ground vibration, air blast, and fly rocks. In this paper, first blasting operation and its possible environmental effects are defined. Then the methods of blast-vibration prediction and commonly accepted criteria to prevent damage were introduced. A field experimental work was conducted to minimize the vibration effects at Saribayir quarry as it is an identical case for the many quarries situated in and around Istanbul, Turkey. Although the local surrounding geology and rock mechanics have great influence on vibrations as uncontrollable parameter, the charge weight per delay, delay period, geometric parameters of the blasts were changed to solve the existing vibration problem in the studied quarry. To obtain a realistic result, 10 blasts were carried out and 30 seismic records were made in different places mainly very close the buildings and the other vulnerable structures around the quarry. The evaluation is performed whether the vibration level are within safe limits or not. The prediction equation based on scaled distance concept is also determined, however, it is a site-specific model and need to be updated when the quarry advances. The safe blast parameters which minimize the environmental effect were determined for the Saribayir quarry.     

Influence of total charge in a blast on the intensity of ground vibrations—field experiment and computer simulation

A number of factors influence the generation, propagation and intensity of ground vibrations. However, there are conflicting opinions with regard to the influence of the blast size on the intensity of ground vibrations. This paper discusses the experiments conducted in an opencast coal mine in India and a simulation study carried out to establish the influence of total charge in a blast on the intensity of ground vibrations. Studies clearly indicate that the total explosive charge in a blast has insignificant influence on the intensity of ground vibrations for distances between 100 m and 3000 m.     

Barrier holes and trench application to reduce blast induced vibration in Seyitomer coal mine

In this research, experimental applications have been performed to reduce blast induced vibrations in open pit mines. For this purpose, artificial discontinuity zones such as barrier holes and trench were opened in a dragline panel of Seyitomer Lignite Enterprise, Kutahya, Turkey. Peak particle velocities in front of and behind them were measured by seismographs. In this way, their effect against vibration was observed and compared. Barrier holes were opened 24 m deep through 3 parallel lines and aligned at 1 m spacing. On the other hand, the trench had 8 m depth and 4 m width. During the research, 209 measurements were taken belonging to 105 explosions. Twenty-eight explosions were carried out in the barrier holes experiments and 77 explosions were carried out in the trench experiments. A decrease in vibration of 14.3–18.5% was obtained behind the barrier holes while a decrease of 24.8–58.1% was provided by the trench.     

Studies on the effect of burden width on blast-induced vibration in open-pit mines

This study concerns the correlation between burden and blast-induced vibrations in open-pit mines. For this purpose, two different mines were studied. In these mines, the vibrations caused by explosions at burdens having widths ranging from 3 to 14 m were measured from various distances. From the results, it was found for these cases that burden width has a significant impact on vibrations. Consequently, it was proven that vibrations decrease as burden increases.     

Blast vibration control in the presence of delay scatter and random fluctuations between blastholes

It is becoming increasingly important, from an environmental viewpoint, to minimize vibrations induced in urban dwellings by blasting. The present study illustrates how the delay interval between blastholes can be chosen to control and minimize the vibration energy within the structural response band of most houses. In particular, it is shown that the only possibility of reducing such energy is to employ a delay interval in the range 10–35 ms. However, the induced vibrations are also dependent upon the accuracy of the delay initiators as well as the level of random fluctuations between each blasthole signature. It is shown that only very accurate electronic delays give the possibility of utilizing fully the delay sequence in order to control structural vibrations. If the vibration emission from each blasthole is totally uncorrelated with that of any other blasthole then the resulting amplitude spectrum of the blast will be totally unpredictable. This situation occurs irrespective of the delay initiation sequence or its accuracy. Under these conditions it is impossible to predict the blast-induced energy lying within the structural response band.     

Newspapers as a validation proxy for GIS modeling in Fujairah,United Arab Emirates: identifying flood-prone areas

Prediction and control of blast-induced ground vibration is a matter of concern in mining industry since long. Several approaches ranging from scaled distance regression, different numerical methods to wave superimposition theories have been tried by many researchers for better prediction and control of blast-induced ground vibration. Signature hole analysis is one of the popular simulation methods to predict the ground vibration generated due to production blast. It superimposes the recorded signature hole waveform using a computer program to predict the production blast-induced vibration. The technique inputs the designated time of detonation of each hole and superimposes the waves generated by each hole to predict the nearest value of peak particle velocity and frequency of blast-induced ground vibration. Although a very useful approach, it requires a computer program to simulate the linear superimposition of waveforms. The simulation is not possible for every blast as it takes time and also is difficult for field engineers to simulate every time, whereas it is always easy for blasting engineers to adapt and use an empirical equation/approach for prediction and control of blast-induced ground vibration than simulation. In this paper, an attempt has been made to develop an innovative and simplified analytical approach of signature hole analysis. The simplified sinusoidal wave equation is obtained from recorded signature hole ground vibration waveform properties and is superimposed mathematically according to the multi-hole blast design to predict the production blast-induced ground vibrations. The validation of the developed approach was done in three different sites, and up to 15% more accuracy in prediction of the blast, vibrations are achieved in comparison with signature hole analysis prediction.

     

Safety Concerns of Ancient Temple due to Blasting in Adjacent Mines

Directives from the Hon’ble Supreme Court of India led to the banning of mining activities within a radius of 2 km of the Sri Jambunatheswara ancient temple in Hospet taluk of Karnataka State of India. On recommendation of the Department of Archaeology & Museums, Government of Karnataka, CSIR-CIMFR undertook extensive investigations wherein the ground vibration and air overpressure due to blasting in nearby iron ore mines were monitored to assess their damage and annoyance potentials. The magnitudes of blast-induced ground vibration and air-overpressure recorded in the temple were found to be within the standard safe limits stipulated by the Directorate General of Mines Safety, India when trial blasts were carried out at a distance greater than 290 m from the temple. When blasts were conducted at a distance of beyond 845 m from the temple, neither vibration nor sound of blasting could be recorded or heard at the temple premises, indicating it a safe zone for blasting. After thorough analyses of the recorded data, precise blast design parameters were recommended for blasting at distances beyond 200 m from the temple and allowing this distance to be demarcated as the safe zone where controlled blasting could ensure safety of the ancient temple.     

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 39 m 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 26 mm, which is acceptable in regard to open pit slope stability.     

Analysis of Ground Vibrations Caused by Open Pit Production Blasts - A Case Study

In order to study the characteristics of ground vibrations caused by production blasts in an open pit gold mine and to evaluate the impact of the vibrations to buildings, a seismic survey was conducted at an open pit mine. Two monitoring lines with multiple seismic stations were surveyed. The first line had a length of 4,492 m and the second line runs approximately perpendicular to the first line with a length of 823 m. The seismographs recorded the particle acceleration, velocity, and displacement in longitudinal, transverse and vertical directions. The magnitudes of peak particle motions were calculated and compared with several established damage criteria used in mining and geotechnical/structure engineering. Empirical equations were established based on the field measurements. Analyses were also performed to exam the effects of geological structures on the attenuation of individual vibration components as well as the peak vector sum of the particle velocity.     

单临空面岩体中爆破诱发损伤的数值分析

岩石的抗压强度远大于其抗拉强度,所以在单临空面岩体爆破中,工程技术人员关注的不仅是炮孔附近的塑性压剪损伤,更多的是临空面附近的拉裂损伤,临空面若是地表,可能会影响到施工的安全,甚至造成一定的经济损失。以往这类损伤问题的数值模拟中大多只偏向于一方面：或忽略压剪损伤,或不考虑拉裂损伤,故所得出的结论难以满足工程需要。基于合理的应力修正方式,把现有的岩石拉-压损伤本构以简明的方式嵌入到大型LS-DYNA软件中,对单临空面岩体中的柱形和球形药包爆破问题进行了数值模拟,计算结果表明该法能较好地预测岩体中爆破诱发的拉裂、压缩损伤的分布规律和演化趋势。     

Ground Vibration due to Blasting in Limestone Quarries

A database of ground vibration due to blasting at 27 limestone quarries, located in various parts of India, has been created. The database contains peak particle velocity (PPV), frequency, other vibration related and blast design parameters. Regression analysis of the data is carried out to derive site constants of the USBM predictor equation for individual quarries. It is found that these site constants are correlated with each other. By combining all the data, a generalised predictor equation is developed to assess and control ground vibration. In addition, mean zone of attenuation has been delineated using the predictor equations of the individual quarries. The dominant frequency of ground vibration with respect to distance and the possibility of modifying it by changing delay intervals in production blasts are also examined.     

Analysis of Blast Vibration Characteristics Across a Trench and a Pre-Split Plane

This paper presents the influence of various discontinuities, natural or artificial, on magnitude and frequencies of blast induced ground vibrations. These discontinuities were geological faults, a pond, a shaft incline, a trench and a pre-split plane interposed in the path of vibration propagation. In the post-trench region, ground vibrations in terms of peak particle velocity were significantly reduced and dominant frequencies in higher bands were consequently observed. Depth of trench with respect to blastholes were varied and consequent vibration characteristics were analyzed. The techniques of creating a trench and pre-split plane were successfully implemented in controlling vibration and in increasing the explosives charge to meet the scheduled production target of an opencast mine. Comparisons of ground vibration characteristics affected by a trench and a pre-split plane of the same depth are described in the text. The findings lead to the conclusion that such experimental data are necessary for production blasting in open cast mines under constrained conditions.     

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.