01 Jul 2016
POSTED BY - MineExcellence
Blasting operations cause several adverse environmental effects. With the development of new explosives systems and initiation devices, blast design and execution techniques, the blasting process has now become more efficient and safer than before. Use of software tools for blast design, support in execution, blast monitoring and analysis makes it possible that damages and dangers from blasting can be predicted before blasting thus adverse impacts of blasting can be controlled and reduced. Software for prediction of vibrations, airblast, wave front reinforcement, flyrock, dust plume movement prediction are tools can be used before blasts to control environ impacts.
Keywords: Blast Design, Environmental Impacts, Software for Predictions, Control of Blasting Impacts, Blast Information
1.0 Introduction
Blasting operations cause several adverse environmental effects: ground vibrations, airblast, flyrock, generation of fines, fumes and dust. It is important to control all these effects while carrying out blasting operations as increasingly projects are being subjected to scrutiny and at times closure. An improper blast can change the balance sheet of a mine due to public litigation cases and payment of heavy compensation. Efficient blasting with reduced environmental effects 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. Conventional blasting practices and techniques in mining and infrastructure construction industry are unable to improve efficiency and mitigate environmental hazards.
With the development of new explosives systems and initiation devices, blast design and execution software tools, the blasting process has now become more efficient and safer than before. Also the damages and dangers from blasting can be predicted before blasting thus adverse impacts of blasting can be controlled and reduced.
Environmental Impact 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 many adverse impacts such as ground vibrations, 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 environmental impact control. Operators need to adopt strategies to control the adverse environmental impact of blasting operations (Figure 1). 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. Therefore, explosives management is carried out which involves delivery, loading and priming. Based on this information environmental impacts can be predicted, which allows explosive and initiation can be changed at the execution
level. Several monitoring tools can be used to evaluate blasting results and analyse outcomes to improve overall operations and control subsequent blasting. Key performance indicators (KPI) can be determined and continuously monitored by management at different levels. Further, statutory reports can be generated easily.
Figure 1 Strategy for adopting to obtain optimum blasting operations.
All the information about blast needs to be recorded in appropriate manner to plan subsequent steps.
2.0 Information Technology Applications in Blasting
Information technology can be used in every step of drilling and blasting operations. Based on customized blast design tools for any operation blast design, charging and execution can be planned. The design can take into consideration environmental restriction and result goals. After holes are drilled then measurements regarding burden, spacing, hole depth need to be made either by using GPS or by manual measurements. There would always be difference between designed hole location and inclination and actual holes drilled. After actual drilling and blasting parameters are available then predictive tools may be used for fragmentation, vibrations, flyrock and dust. Information can be used for simulation of firing sequence and for checking any unfired holes. If drilled blast is likely to exceed respective limits then charging, initiation timing and sequence can be changed to keep adverse environmental impacts within defined limits.
Drilling and blasting data management system ensures information storage, but also acts as an intelligent system as an aid for blast design, prediction of impacts and analysis. Data is obtained from blast hole face profiling tool, vibration prediction tool, and direct data link to a database incorporating all the major manufacturers products and an interface allowing the user to add new product ranges and create custom products. Misfire and accident details can be recorded.
If data is continuously recorded then large number of data becomes available, the system can up-date scaled distance relationship, based on location variations and ultimately provide the blasting engineer with an interactive means to assist with planning of future blasts.
3.0 Surface Blast Designer
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 that considers factors that 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. 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. This is in conjunction with field observations, experimentation and monitoring. Blasts can be designed while using scaled distance tools so that vibrations—ground and airblasts are within limits. This needs to be checked for permitted limits. Information Technology can be used to design blasts based on historical data collected over a period for each geotechnical strata and provide optimized drilling and blasting patterns. There are several blast design software tools. These can be tailored according to needs of a project. Every blast block can have appropriate blast parameters. For example Surface Blast Design Software (BLADES) can be tailored for use by any organization. Figure 2 provides a typical blastdesigned by this software. The software allows easy design of blasts, calculates blast parameters i.e. burden, spacing, square/staggered pattern layout, and layout with charging options. The program provides output, charts and graphs, as well as reports in real-time and allows output of data via customizable printing capabilities.
Surface blast design software BLADES provides design of blasting pattern according to rock conditions, rock structure, and results required for optimized results, considering explosives, drilling, environmental restrictions and equipment and subsequent operations. It provides delay timing and sequence, the pattern drawn can also be saved and blaster can be provided with charging sheet. It also provides the first movement of rock. It gives approximate vibration values, fragment size and approximate danger zone. Initially the software uses constants which are empirical. However, after data have been accumulated with use of BIMS then the historical data can be used to determine specific constants for each pit/bench. Predictions of rock fragmentation air and ground vibration prediction and flyrock are estimated. Software has drilling and blasting cost analysis capabilities. The software shows the simulation of ignition sequence. Initially the software uses constants which are empirical. However, after data have been accumulated with use of database software then the data can be used to determine specific constants for each geotechnical zone of bench to design specific bench wise blast design. Software can import/export drill hole data, GPS data, total station records, face profiler records in excel or .csv file. The software can give charging sheet for blaster for loading explosive in each hole and also provides initiator connection. The software also provides reports as needed for individual operations or as per format of regulatory authorities. Blades software can be
Figure 2 Surface Blast Designer software BLADES provides design for a blast block.
used to create charge standards to design specific hole by hole explosives loading and create load sheets according to geotechnical zone characteristics and required results.
4.0 Blast Information Management System (BIMS)
Blast Information Management System (BIMS) provides information to meet the strategic and operational needs for planning, controlling and decision-making for optimizing mining operations (Bhandari and Bhandari, 2006). BIMS 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 (Figure 3). 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 instead of days for manual methods. Readily available past data in a logical format and blasting data analysis tools are the key features of the database. The database can be extended to integrate with other systems such as ERP, CMMS etc. 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 popular mining software makes it is possible to reduce input work. Entered data can be edited through edit parameters functionality. Protection and regulatory authorities are increasing their expectations for strict accounting of inventory and blast documentation. Blasting company executives and managers are now facing the possibility of incarceration, fines and suspended operations if their documentation
is not in order. The database can be tailored according products and practices, of customer requirements.
This database has also 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.
Figure 3 Blast information management system
Presentation of analysis of data, compliance reports suitable for regulatory bodies, archiving and viewing of data at distance location, costs can be developed. Reports suitable for Occupational Health and Safety (i.e. incident reports) can be compiled. Key Performance Indicators (KPI’s) are derived. This tool provides a way of trapping the experience of drilling and blasting personnel to better control critical parameters such as dilution, vibration, fragmentation, and flyrock and fines generation. Integration with other software such as that used for vibration monitoring and analysis, fragmentation size analysis, vibration wave front reinforcement analysis etc. can be carried out so as to provide simplified management system.
5. Prediction and Control of Environmental Impacts
Actual drilled data can be used for predicting environmental impact of blasting and if the environmental limits for vibration and flyrock imposed by regulatory authorities or by management exceed then explosive charge distribution and initiation timing and sequence can be changed so that limits are not exceeded.
5.1 Blast vibration prediction and compliance
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. Key features include:
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 (Figure 4).
Figure 4 Determining Scaled distance by regression analysis
5.2 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. The model allows for the time taken for blast vibration wave fronts to travel from each blasthole, and has been successfully used to explain the reason for directional increases in both air and ground vibration in certain situations (Richards and Moore, 1995). The model has been used to identify wave front reinforcement due to the propagation of air vibration and ground vibrations in certain situations. Simple alterations to firing patterns can prevent wave front reinforcement and be used to control vibration levels in many situations. 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. 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 analyse the layout and initiation sequence of blasts. The analysis module also provides tools for doing detonation simulation, viewing fired and unfired holes, time window simulations and reporting. The detonation simulation tool allows the user to view the detonation sequence of the blast and visually assess the design prior to blasting. This helps the designer to assess the movement of the blast area.
Figure 5 Wave reinforcement with 25 millisecond delay which can be removed with 42 millisecond delay
5.3 Flyrock prediction software
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 ‘design your own flyrock’ 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 (Richards and Moore, 2004).
Figure 6 Prediction of flyrock distance
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 and ensure that flyrock does not reach that site.
5.4 Dust Plume Movement
Blasting operations can generate large quantities of fugitive dust which, when released in an uncontrolled manner, can cause widespread nuisance and potential health concerns for on-site personnel and surrounding communities. Though the blasting dust plume is raised for few minutes but most of the dust settles in and around mining area and some of it is dispersed before settling down. Depending on meteorological conditions the dust dispersal can travel to substantial distances endangering health of communities. Generation of fines and dust is influenced by several blasting and rock parameters (Hagan, 1979, Bhandari et al, 2005). The type of explosives used and the manner in which they are charged in the hole determines the amount of fines and dust generated during blasting. Similarly blasting parameters such as burden, spacing, subgrade and delay timing have effects on the generation of fines & dust. Type of rock and stemming material, including the amount used in the hole, also play an important role in the generation and raising of dust into the atmosphere.
Meteorological conditions such as wind speed and direction, temperature, cloud cover and humidity will affect the dispersion of airborne dust. Atmospheric stability affects dispersion of the emitted plume, determining the extent of the vertical and horizontal, transverse and axial spread of the emitted particulates. Thus, dispersal of dust plume resulting from blasting is an important area which needs attention. A computer model has been developed to simulate the dispersal of dust (suspended particulate matter) resulting from blasting operations in surface mines. The mathematical solution has been provided (Kumar and Bhandari, 2001, 2002). Data input form is shown in Figure 7. This is divided in three parts: blast data, atmospheric data and ground contour data. (i) Blast Data: Total quantity of dust released, Distance in meter from the blast to the point of observation, Angle of top of column of dust of the blast, Latitude of blast site, Height of blast site (above mean sea level).
(ii) Atmosphere Data: Surface Pressure, Variation from mean wind speeds: Standard variation of speed in meter per second. This is obtained by observation at the blast site in the straight line. Saturation Mixing Ratio: Mixing condensation level: Surface Wind direction. (iii) Ground Contour Data: This data is collected by the user before the blast with the help of contour map.
Then the software computes the values of the concentration at different distances in the down wind direction of the surface wind at level (zi) at horizontal interval of _____ m and at lateral distances from the central line on either side at the lateral interval of ____m up to ____m for all (zi) varying from 2m agl (above ground level) to 24 agl in steps of 2m. 3D axis on the point of blast is drawn and converts the x; y coordinates to 3-D coordinates and plots them on the 3-D- coordinate system. Then the movement of plume at different levels is distinctly shown. The software display shows 3D movement of plume. A typical display is given in Figure 8. This prediction allows one to delay blasting and use suitable atmospheric conditions and prevent blast plume to go to a particular site.
Figure 8. Movement of dust plume after blast
6. CONCLUSIONS
Blasting operations urgently needs to use extensive information technology. Use of information technology for storing data, design, analysis and prediction of results helps in better control and optimization of mining operations. Data base 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 due to adverse impacts of blasting and can improve efficiency.
REFERENCES
Bhandari, S. & Bhandari, A. 2006.; Blast Operations Information Management System, Journal of Mines, Metals and Fuels, Vol. 54 no.12
Bhandari S., Bhandari, A. and Arya, A., Dust Resulting From Blasting In Surface Mines And Its Control, EXPLO 2004 Conference, Perth, 2004.
Hagan, T.N. 1979. “The control of fines through improved blast design”. Proc. Aust. Inst. Min. & Metal. pp 9.
Kumar, P. and Bhandari, S. 2001 “Modelling dust dispersal near source after opencast mine blast in weak wind conditions over flat terrain in tropical conditions”, Explo 2001 Conference, Hunters Valley.
Kumar, P. and Bhandari, S. 2002 “Modelling dust dispersal near source after surface mine blast over undulated terrain in weak wind conditions, APCOM –2002, Phoenix
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,