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24 Jun 2016

Application Of New Technologies For Optimisation And Environmental Controls Of Blasting Results

POSTED BY - Gulshan Kumar


1. INTRODUCTION

A number of new technology applicable for drill and blast operations are now available to improve productivity and profitability of mining operations, optimise ore extraction and extend the life of mine. Blasting is an operation which affects all subsequent operations and costs. All of the activities – blast location, pattern design, selection of charge type, charge amount and distribution, mark up to drill, charge and stem, decide on initiation and tie-up and safety precautions and blast -- are linked in a sequence because they must be carried out in a certain order. While carrying out blasting process there is no measurement and control at different stages. Compliance audit of execution is often absent as only some steps are checked. However, by using new technology, in an integrated manner the drill and blasting team can alter the blast charging, initiation sequence and tie-up just before the blast in the field to improve results. 

There is often difference in designed and actual drilled holes. Actual drill data can be used for predicting impact of blasting and if the environmental limits for vibration and flyrock imposed by regulatory authorities or fixed by management exceed then explosive charge distribution and initiation timing and sequence can be changed so that limits are not exceeded. 

Efficient Blasting and Environmental Control Strategies

 Essentially, the energy released by the explosives is useful for fragmentation, displacement and movement of broken rock whereas wasteful part of energy causes so many other impacts such as ground vibration, airblast, flyrock, dust and fumes. A blast with poor fragmentation is likely to have a higher than expected environmental impact. The key therefore, is the effective blast design and proper implementation for both efficient blasting and control of environmental impact. Figure1 the diagram explains systematic manner in which consideration of geology and mine planning information, blast block location, environmental information is provided for design of blast. Based on the blast design, drilling operations take

place and measurement of actual drill hole position is recorded. This actual hole location information is then used to predict the blast results before hand. Based on these predictions explosive and initiation can be changed at the execution level in consultation with team. Explosives management is then carried out which involves delivery, loading and priming. Several monitoring tools can be used to evaluate blasting results and analyse outcomes to improve overall operations and control subsequent blasting. Key performance indices (KPI) can be determined and continuously monitored by management at different levels. 

 2. Blast Planning and Design

 Optimum blasting just does not happen. It requires suitable planning, good blast design, accurate drilling, the correct choice of explosives and initiation system and methods, adequate supervision and considerable attention to detail. An approach is needed to consider the factors that can interact with each other during blasting. The rock type and structure; size, length and inclination of blast holes, drilling pattern and accuracy, type, quantity and distribution of explosives; charging and initiating techniques all play a significant role in the overall efficiency of a mining operation. During the design stage environmental constraints such as vibration limits or flyrock restriction with respect to any structure can be prescribed. Similarly fragmentation size distribution muck pile movement need to be considered. Blast design software can be used which considers all the above aspects. The software can be used as a tool to assess the likely impact or effect of a particular design on results in terms of fragmentation, movement and other environmental impacts.

 In general current practice is to print out a list of hole numbers hole positioning and hole dipping, and a plan of their position. This is taken to the bench, where each hole must be located manually, measured with a tape measure and the hole depth written onto the print-out list. At the end of the shift, this is taken back to the blast designer, who then manually enters this data into the blast design software to generate loading sheets. The automatic hole dipping

system is uploaded with drill hole numbers and GPS coordinates of each hole via Wi-Fi from the blast design software. On the bench, the hole is identified and measured, with information transmitted to the blast design engineer; real time data comprising the actual hole position, depth, and depth of water which might be in the blast hole. The blast hole load sheets are generated using this information. After the holes are drilled, a low cost sensor cable is placed in each hole, and the cable is prewired to a wireless transmitter. Before the hole is loaded with explosives, the sensor cable monitors the depth (cave-in detection), depth of any water present, and hole temperature. This information is used to plan the blast hole loading and identify hot holes. During loading, the sensor cable monitors depth of the explosive column as the explosive fills the hole. After the holes are loaded with explosive products, the same sensor cable is used to monitor density and temperature of the products. Subsequent data can be used to: 

  • Monitor the holes during sleep time, and ensure that the density is not approaching to a critical value
  • Detect any water ingress of explosive products (due to a decrease in density and temperature)
    • Identify any reactive ground reactions (due to a significant temperature increase). 

At detonation the same sensor cable is used to measure the Velocity of Detonation. Remote control drill rigs have been developed and used in Australia. A company in the USA offers a service to retro-fit out the drill rigs for remote operation.

 Additionally, for bulk mining operations, the development of bulk explosives trucks (MMU) will enable faster explosives production and delivery. Current practice for wet holes is to pump explosives into the blast holes by placing a hose at the bottom of the hole and raising it as the hole fills with explosive (displacing the water). This is very slow when you’re charging hundreds of deep holes.

 3. Blast Information Data Base

 Blast data base provides methods to store, manage, document and retrieve drill and blast related information. The system stores blast details, actual blast parameters, blast pattern, face profile, explosive consumption, charging details.

 The stored blast information data can be retrieved quickly and easily. Performance and cost of blasts can be monitored and appropriate blast designs for particular areas or different zones can be identified. The data management and retrieval is easy and simple to use which can be carried out in a few minutes which helps in optimizing various operations. Readily available past data in a logical format and blasting data analysis tools are the key features of the database. If the software is operated in conjunction with a comprehensive monitoring program, it can contribute to the efficient running of an operation and reduce environmental effects to a minimum. Importing data from .csv file, Excel and other mining software makes it is possible to reduce input work. Entered data can be edited through edit parameters functionality. The database can be tailored according products and practices, to customer requirements and can be maintained. This database also has searching options using which the user can look for the records of blasts as per his defined criteria. The software can use several criteria for the search option: between dates, by performance of explosives or

initiating system, by vibration limits, by fragmentation size, by location of blasting zone or accident etc.

Integration with other software used for vibration monitoring and analysis, fragmentation analysis etc. can be carried out so as to provide simplified management system. The system also provides defensible data that can be provided to regulatory authorities to illustrate the mine operator’s compliance with regulations. 

Web based Database

 The cloud based computing system allows for storage and retrieval of all blast related data as well as the ability to mine the data. Data mining is the process of analysing data from different perspectives and summarising it into useful information. This information can be used to make engineering or business decisions on the drilling and blasting program. For predicting results clients should login to a website that stores all the system’s monitoring data. After login blasting predictors page will open from that user can check seismic data and corresponding blasting logs available in an organised, sortable manner as shown in Figure2. They can calculate air vibration, ground vibration, wave reinforcement etc and can generate numerous graphs to view historical trend analyses that can help identify areas of the pit that may require a change in blast design before serious problems arise. Compliance graphics allow for at-a-glance feedback on how a blasting program conforms to applicable ground vibration and air overpressure limits. If away from the office and computer, a smart phone app is available which allows access to data using your Android or iPhone.

4. Prediction and Control of Environmental Impacts

Increasing numbers of mining operations are coming under pressure to monitor and reduce blasting related safety and environmental hazards (Bhandari, 1997). Ground vibrations, air over-pressure, fly-rock, dust, blasting fumes in some cases leaching of chemicals in the blast

holes and polluting ground water are some of the undesired events associated with blasting which collectively affect the surrounding environment adversely.

Much work has been carried out on the environmental aspects such as ground vibration and airblast control Operators are now aware about the steps which need to be taken. Norms and standards regarding ground vibration and air blast as specified by regulating agencies must be complied with. It is therefore, vital for the industry to do all that it can to reduce the vibration levels experienced at these adjacent properties without imperilling the financial viability of the enterprise. 

Blast Vibration Prediction

A comprehensive blasting analysis and reporting software vibration predictor meets the needs of both operators and regulators. It supports and improves compliance with blasting related planning conditions, and contributes to improved blast performance and blast design.

 Much work has been carried out on the environmental aspects such as ground vibration and airblast control (Richards and Moore, 2002). Operators are now aware about the steps which need to be taken. Norms and standards regarding ground vibration and air blast as specified by regulating agencies must be complied with. In India adequate regulations do not exist with respect to ground vibrations and airblast vibrations. Self regulatory limits need to be set by the organizations while taking neighbors into confidence. Current norms were initially intended to prevent structural damage to adjacent properties, however nowadays they are being employed in an attempt to minimize human nuisance. Thus these values are now set at much lower levels than those based on damage criteria but still above human perception level and as a consequence complaints still arise. A statutory vibration limit be included on a sites operational license which must be adhered to at a specified confidence level at the nearest occupied property. It is therefore, vital for the industry to do all that it can to reduce the vibration levels experienced at these adjacent properties without imperiling the financial viability of the enterprise. 

When these contours are superimposed on the site plan or photo, the maximum extent of vibration levels for blasting anywhere in the mine on the surrounding area can be seen. Scaling

methods have been used for many years to determine relations between charge mass distance and blast vibration levels. The vibration is predicted by either square root or cube root scaling formulae relating vibration to charge mass and distance for a particular site. Excessive air and ground vibration are then controlled by a reduction in the explosives charge mass being fired at the one instant of time, or within a small time period of up to 8ms. These scaling methods do not allow for the time taken for vibration wave fronts to travel from each blasthole, and cause reinforcement of vibration wave front.

Regular updating of predictions using ongoing site data, providing minimum instantaneous charge (MICs) to the operator that ensure compliance with vibration level restrictions by design rather than by accident. The system’s advanced analysis also allows blasting on individual benches or areas to be assessed and the financial and environmental risks and benefits of changes to be evaluated rapidly and reliably, optimising costs and maximising efficiency.

 

Wave Reinforcement Predictor

Wave front reinforcement has been found to cause substantial increases in both air and ground vibration from both surface and underground blasting operations. Simple alterations to firing patterns can prevent wave front reinforcement and be used to control vibration levels in many situations. Pattern Analyser is a graphical software program for the design and editing of blast designs. It gives engineers and blasting personnel the ability to design and optimise the layout and initiation sequence of blasts. Analysis of data imported from other software can be carried out.

By change of delay timing or sequence reinforcement can be avoided thus lowering of maximum vibration levels. This tool allows blast to be designed to reduce exceedance of vibrations both for airblast and for ground vibrations.

 

Flyrock Prediction Software

Damage due to flyrock from blasting is one of the main cause of strained relations between quarry management and neighbors. Flyrock distances can range from zero for a well controlled mine blast to nearly 1.5 km for a poorly confined large, hard rock mine blast.

Inputs to the software are charge mass, burden or stemming height, and a site constant that lies within a general range that can be tightened by site calibration. The output is the distance that rock will be thrown, and this quantification can be used to establish both safe clearance distances, and the critical range of burdens and stemming heights where the situation changes rapidly from safe to hazardous.

Zone of flyrock travel is indicated by this tool. Using safety factors, danger zones for machinery and persons respectively. If it is not possible remove any structure or person then one can change charging of holes.

Fragmentation Size Prediction

Over the past decades, significant progress has been made in the development for blast design and blast fragmentation size prediction. Rock fragmentation depends on many variables such as rock mass properties, site geology, in situ fracturing and blasting parameters and as such has no complete theoretical solution for its prediction. However, empirical models for the estimation of size distribution of rock fragments have been developed such as those based on the Kuz–Ram fragmentation model. This method is able to predict the entire fragmentation size distribution, taking into account intact and joints rock properties, the type and properties of explosives and the drilling pattern. This type of predictions allows design of blasts according fragmentation size requirements (Cunningham, 1983, Engin, 2009).

Web Based Fragmentation Predictor

Fragmentation Predictor will allow user to ‘design most optimized blast design with minimum cost’. Inputs to the software are Blast design information, Rock properties information and explosive information and based on Kuz-Ram fragmentation modeland Rosin Rammler equations, this model enables to make fragmentation calculation,graph and table between fragment size and percentage passing. Figure 6 shows the fragmentation size distribution result as per the design parameters of blast.

Input Design Parameters

Signature Hole Analysis

Single-hole signature analysis allows computer simulation for thousands of potential blast designs that can be evaluated at each monitoring location. The vibrations from each single hole shot being fired in a certain area of the pit will produce ground vibrations with a resulting frequency spectrum dictated by the source/receiver path (geology). Testing has found that this frequency spectrum or geologic response is primarily a function of the overburden thickness. Because houses amplify only certain frequencies, it is possible to synthesise the frequency spectrum from hundreds of potential blast designs for each location of concern, and identify the blast patterns least likely to affect the neighbouring houses. By reducing the amount that the houses shake, complaints are reduced. This integrated approach of available technologies provides an intelligent, scientific solution for blast vibration remediation.

5. MOBILITY SOLUTION

In recent years, there is growing convergence of “consumer“ technologies that we are using every day on our iOS and Android devices such as camera, motion sensors, and GPS systems (Akella et al, 2008, McHattiee, 2013). Use of Mobile devices makes it easier to collect data on site and it mainstream in many places where mobile workforce is present. Use of these devices would be ideal in the field for Drill and Blast personnel. They would get the required capability of collecting on-site-blasting details. As part of the technology solution a Mobile App has been developed which has the following features:

 Figure 7 shows basic concept of mobility solution. To use this application, mining personnel can take the device to blasting site in android or iOS device to the blasting site. All parameters related to drilled holes and explosive charging, stemming etc can be collected. At this stage blaster can recheck predicted fragment size distribution, flyrock distance, ground and air vibration, fragment size etc and if there is variation from designed and limits are exceeded then changes in charging, stemming, initiation devices and timing can be done before executing the blast. Photographs and videos can also be saved using capabilities of the device. Data can be imported from other devices or tools such as vibration monitoring record.

When mining personnel returns from site, he can sync this data to the web version of this application and export it as well to the desktop because local storage of mobile devices cannot save large amount of data. Figure 8 gives example of flyrock prediction. Figure 9 gives details of fragmentation prediction steps. Similarly this tool can be used for ground vibration and air blast prediction. Simulation and wave front reinforcement analysis can be carried out.

CASE STUDIES

Two limestone open pit mines are using initial formats webbased/ desktop modules of predictors and data gathering. These mines use the solution before a blast is carried out, actual drilled hole locations are measured and predictors are used to check fragmentation results, vibration and flyrock distance and if necessary explosive charge loading, delay, initiation sequence are altered for controlling environmental impacts. The use of this has improved safety, improved environmental impact and reduced drilling and blasting costs. In one year there has been improvements and cost reduction.

Aditya Limestone Mine:

Aditya limestone open pit mine is designed to produce limestone 6.6 million tonnes per annum. Presently, there are two working pits. Working pits have been developed with working benches of 9.0 m. height. Drilling is done with the help of ROC L6 and IBH-10 drill machines of 100mm -115mm diameter. The ore to overburden ratio is 1:0.33. Thus, total rock handling is around 9 million tonnes per annum.

This mine has been able to store blast related data from the beginning of limestone open pit mine in 1965 till date. Mine used to keep blasting related data initially in hand written format and thereafter they used to maintaining records in Excel sheet format. This has helped the

mine in improving drill factor from 45 tons/m to 75 tons/m, breakage of limestone from 6.5 tons/kg to 14 tons/kg of explosive thus reducing costs by 50% while improving crusher productivity from 764 tons per hour to 932 tons per hour and controlling vibration, flyrock and dust.

In 2011 Aditya mines obtained and started using Blast Information Management System software in a client server version (Parihar and Bhandari, 2011). This software stores data related to regarding blasts taken in the mine which provides the facility of data retrieval in a number of ways. By keeping records, mines have been able to reduce costs and improve blasting operations. Using analytical facilities in the tool it was realised through fragmentation size records that while overall blasting costs reduced but transportation and crushing costs increased. After maintaining powder factor around 15 tonnes/kg for almost a decade, the mine increased explosive consumption by changing powder factor to 13.81 tonnes/ kg and could see improvement in crusher performance and excavator performance. After entering the required above data, software provides facility to produce blast reports along with photographs and also blast videos. Data management system provides the ways for better and systematic management of the blasting operations for the mine of longer periods.

From the data analysis it was realised that even after reducing size of blasts to maintain vibration level below 5 mm/s (that as per regulatory standards mine was getting complaints from nearby villages. Data was examined showed that airblast levels were exceeding in several cases above 115 dB. These blasts meant that people were experiencing inconvenience the nearby villages and were complaining. Mine obtained software for wave front reinforcement analysis of drilled pattern before carrying out a blast to check for reinforcement of ground and airblast vibration levels and to look for number of holes going together in a given time window.

 

Injepalli Limestone Mine

Injepalli mines of Vasavdatta Cement produces 9.00 million tonne limestone per annum. Bulk mixed ANFO and Raydet shock tube initiation are used in their blasting operations. Mine is using Sandvik DI-500 drill machine with 155mm hole diameter and bench height varies from 5.0 m to 12.0m.

Mine started using some modules of integrated blasting solutions software for collecting blasting data and predictors in May 2014. With the use of these solutions, the organisation is getting cost effective results. Previously, the mine was using the drill pattern with burden of 5.5 m, spacing of 10.0 m and hole depth as10.0 m (With these parameters as, powder factor 11.60 tons per kg, drilling factor 108.79 tonnes per meter, cost Rs.3.0 per ton. tonnage per hole as 1375 ton. In year 2013-14, the mine was using the pattern with burden of 5.5 m, spacing of 10.0 m and depth as10.0 m. Analysis of data records of the previous blasts helped and pattern was gradually changed to burden of 5.25 m, spacing to 11.0 m and hole depth of 10.0 m. Changes in blast parameters shows results in that cost reduced to Rs 2.8 per ton with powder factor improved to 12.29 tonne per kg and drilling factor of 111.18 tonne per meter and tonnage per hole increased to1443 ton (per hole getting 68 ton more). Thus results showed improvement as compared with the previous blast design.

 

CONCLUSIONS:

Blasting operations needs to use innovative technology. Blast engineers are ideally trying to predict three outcomes in blast design: fragmentation (the size distribution of the blasted

material), movement (where the grade and waste will end up), and environmental consequences. The mining industry is using modelling tools that can predict ore movement to minimise the twin evils of loss and dilution. Use of information technology for storing data, design, analysis and prediction of results helps in better control and optimization of mining operations. Data storage helps to quickly respond to information and remain successful in today’s competitive market place. By use of information technology many projects can reduce complaints and can improve efficiency. Several technologies are being adopted in mining industry to make blasting operations efficient and reduce environmental impact.

 

References:

 

  • Akella, J., Kubach, T., Löffler, M. and Schmid, U., 2008 Data-driven Management: Bringing More Science into Management, McKinsey Technology Initiative Perspective, 2008
  • Bhandari, S. 1997, Engineering Rock Blasting Operations, A.A. Balkema Publishers, Rotterdam, Netherlands / Brookfield, U.S.A., 370p
  • Cunningham, C.V.B., 1983 The Kuz-Ram Model for Prediction of Fragmentation From Blasting, First International Symposium on Rock Fragmentation by Blasting, Lulea, Sweden, August, pp 439-454
  • Cunningham, C.V.B, 1987 ;Fragmentation Estimates and the Kuz-Ram Model – Four Years On, Second International Symposium on Rock Fragmentation by Blasting, Keystone CO, August 1987, pp 475-487
  • Engin, I.C., 2009: A. practical method of bench blasting design for desired fragmentation based on digital image processing technique and Kuzram model. In Proceedings of the 9th International Symposium on Rock Fragmentation by Blasting. Granada, Spain; 2009. p. 257–63.

              McHattie, L. (2913) Advances in Mine Engineering to enable Information Mobility for “Intelligent Mine”. ISARC’2013, The 30th International Symposium on Automation and Robotics in Construction and Mining, 11 15 August, 2013, Montreal, Canada

 Parihar, C.P. and Bhandari, S, 2011. Improving Blasting Operations Using Data Management and Analysis, Tenth International Symposium on Rock Fragmentation by Blasting, New Delhi

 Richards, A. B. and Moore, A. J., 1995: Blast Vibration Control by Wave front Reinforcement Techniques in Explo 1995, pp 323-327 (The Australasian Institute of Mining and Metallurgy in association with The International Society of Explosives Engineers: Brisbane).

 

  • Richards, A B and Moore, A J, 2004: Flyrock Control – By Chance or Design? Proc. 30th Ann. Conf. on Explosives and Blasting Technique, International Society of Explosive Engineers,Paper was presented at BME’s 20th Annual Drilling and Blasting Conference in 2012.

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