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  • 1.
    Danielsson, Markus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Navarro Miguel, J.
    Universidad Politechnica de Madrid.
    Johansson, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Utilizing production data to predict operational disturbances in sublevel caving2017In: Mine Planning and Equipment Selection (MPES 2017): Proceeding of the 26th International Symposium on Mine Planning and Equipment Selection Luleå, Sweden, August 29-31, 2017 / [ed] Behzad Ghodrati, Uday Kumar, Håkan Schunnesson, Luleå: Luleå tekniska universitet, 2017, p. 139-144Conference paper (Refereed)
  • 2.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Assessment of rock mass quality and its effects on charge ability using drill monitoring technique2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    For an efficient mining operation, it is essential to have as much information as possible aboutthe ore to be excavated and the rock masses surrounding the ore. Geological information andthe content and distribution of extractable minerals, are central concerns for long term mineplanning. However, for mine stability and production scheduling, the mechanical conditionsof ore and side rock are also very important. The underground mining process normallyconsists of a number of unit operations, such as drilling, charging, blasting, loading,transportation, hoisting etc., linked in a production chain. The quality of the initial operations(drilling, charging and blasting) normally defines the pre-conditions for the following loadingand transportation processes in the mine. The ability to fully charge holes as planned has beenidentified as one of the major obstacles for smooth fragmentation. Course or unevenfragmentation will, for example, significantly affect the loading and transportation efficiencyin the downstream production chain.Earlier studies in LKAB’s Malmberget mine have shown that the chargeability is on averagearound 90%. However, individual levels can have an average chargeability of only 70% andindividual rings, at those levels, can suffer from chargeability as low as 50%. A significantpart of these problems has its origin in geo-mechanical problems in the rock mass. Therefore,detailed knowledge of the rock mass condition surrounding the boreholes is essential toimprove the planning and execution of the charging works in a mine and to improve overallfragmentation and production efficiency.The focus of this thesis is therefore to define and evaluate geo-mechanical features in thedrilled rock mass effecting chargeability, and to evaluate drill monitoring technique for theassessment of rock mass quality and its effects on borehole’s chargeability using hydraulic In-The-Hole (ITH) percussive drilling.The research is based on literature review, drill-monitoring data, borehole filming, on-lineproduction database and monitoring of charging operation. Statistical methods are used toanalyse drill data. The data have been collected from LKAB’s underground mine inMalmberget, Sweden.Several rock mass conditions including caving, shearing, deformation, fracturing, cavities,solid rock, etc., have been identified during filming of 361 production boreholes.Measurement While Drilling (MWD) technique has been used to assess the quality of thepenetrated rock mass. In order to do so, a detailed analysis of the drilling system and thedrilling control including how monitored parameters relate to each other and to the penetratedrock mass conditions, has been performed. The results show that the MWD data containpronounced hole length dependent trends, both linear and step-wise linear, for mostparameters. By combining the borehole filming and the analyses of monitored drillparameters, the drilling responds to each geo-mechanical features in the rock mass is furtherdemonstrated. High correlation has been found between the geo-mechanical rock properties(fractures, cavities, solid rocks, etc.,), and the registered drilling system’s response. Theanalyses show that the responses from the drill monitoring system can distinguish between solid rock, fracture zone, cavity and cave-in. Based on the correlation between the registereddrilling system’s responses and the geo-mechanical features, a geo-mechanical model isdeveloped to assess the borehole chargeability. Principal Component Analysis (PCA) isperformed to model this relationship. The developed model can distinguish fans, or parts offans, with solid, non-fractured rocks where no chargeability problems can be expected, fromfans, or part of fans, with fractures, cavities or cave-in risks, where chargeability problemscan be expected. The model shows high potential for identifying charging problems in theborehole, and has been verified and validated by following an actual charging operation in thereal production environment.

  • 3.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rock Mass Characterisation Using Drill Performance Monitoring: Problems, Analysis challenges and Limitations2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In open pit mining, it is important to know as much information as possible about rock masses to be mined for more cost-effective mining operation. In rock engineering perspective, information about rock mass characteristics usually includes hardness of the rock, geological features, fractures, faults, ore contacts, water bearing stratum. The information about large scale rock mass characterisation is still based on traditional methods such as widely spacedcore drillings, geological mapping of exposed walls, analysis of drill cutting, etc but these methods involve uncertainty about rock mass characteristics in uncored areas. In addition, they are expensive and time consuming. The need for more inexpensive methods providing high resolution rock mass characterisation over large mining areas is therefore a priority forfuture mining industry. Measurement While Drilling (MWD) is a well-established drill monitoring technique which provides information about the rock mass in each production hole. This technique is inexpensive and also ensures high resolution information. By using this technique, drill parameters such as penetration rate, feed force, rotation speed, rotation torque and air pressure are recorded during production drilling which can be used to characterise the penetrated rock mass. However, recorded parameters are not only influencedby the variation of rock mass characteristics; they are also affected by the operators, rig control system interventions, bit wear and measurement errors. In order to use this large amount of data on recorded parameters for the purpose of rock mass characterisation, it is necessary to improve our existing understanding about the contribution of all the influencingfactors and to develop the techniques for identifying and minimising the effect of those factors on rock mass characterisation. The focus of this thesis is to evaluate Measurement While Drilling (MWD) system as a tool for large scale rock mass characterisation in rotary blast hole drilling. In this thesis, researchmethods mainly include literature review, data collection, processing, integration, and analysis. The data have been collected from one of the operating open pit mines in Sweden. Multivariate analysis has been performed to assess the wear of the bit. This thesis presents an attempt to evaluate recorded penetration rate and calculated specific energy for rock mass characterisation. Penetration rate is considered as resistance to crushingof the rock while the calculated specific energy is taken as an index of the mechanical efficiency of a rock working process. The analysis shows that horizontal maps of penetration rate and specific energy (hole average) value reflects the variation of rock mass characteristics in a bench. The areas in the bench which have comparatively higher penetration rate and lower specific energy reflect possible interaction between the bit and soft or weak rock orheavily jointed rock. In contrast some areas in the bench have a relatively lower penetration rate and higher specific energy, indicating possible interaction between the bit and hard rock. In addition, using penetration rate and specific energy values between two subsequent benches indicate similar boundaries among the penetrated zones. When plotting specific energy against penetration rate in each bench, a clear inverse non-linear relationship has beenfound between those parameters. This correlation indicates that penetration rate and specific energy can indicate rock mass behaviour. Further, statistical analysis is done to observe the statistical significance of penetration rate and specific energy values among the different penetrated areas in the bench. The results indicate that penetration rate and specific energy can be used for characterizing large scale rock masses. In addition, information about the rockmass in the upper bench can possibly be used in the next bench to improve production planning. However, hole by hole analysis shows penetration rate and specific energy are influenced by bit wear, hole depth variables, flushing system, operator influence, drill control system, etc.Principal Component Analysis (PCA) shows that penetration rate and specific energy reflecting the change of rock mass characteristics basically are not correlated to bit life length. The bit life length seems instead to be well correlated to the operational parameters such as rotation torque, rotation speed and to a minor extent feed force. Conclusions from PCA analysis must be conservative since the explanation rate for the first two components islimited to 56.5%. Further, the analysis shows that recorded penetration rate has a negative trend with the increasing hole depth. The calculated specific energy has a positive trend with the increasing hole depth. This means that recorded parameters are influenced by hole depth variables.The flushing system also influences recorded parameters. The analysis shows that constant air pressure from the collaring point to the end does not give a clear indication of better flushing system as frequent joints and regular water ingression usually cause fluctuation of pressure.Some of the above mentioned problems can be handled to minimise the effect of influencing factors on recorded parameters. The direct effect of bit wear and hole depth dependency can be minimised by generating a horizontal map of recorded data (e.g. penetration rate) over a large area in the bench. Hole depth dependency on recorded parameters can also be neutralised by performing normalisation based on a regression line using simple geometry. Inshort, the effect of influencing factors on the recorded parameters obtained by using the Measurement While Drilling technique can be minimised and, this technique, in turn, can become a useful tool for large scale rock mass characterisation.

  • 4.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Danielsson, Markus
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Falksund, Hanna
    Luossavaara-Kiirunavaara Aktiebolag (LKAB), Malmberget.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Assessment of rock mass quality using drill monitoring technique of Hydraulic ITH drills2017In: International Journal of Mining and Mineral Engineering, ISSN 1754-890X, Vol. 8, no 3, p. 169-186Article in journal (Refereed)
    Abstract [en]

    A rock drilling system always responds to variations in the mechanical properties of the penetrated rock mass. Combining the drill response with a detailed understanding of the drill system has the potential to give a detailed and high-resolution characterisation of the penetrated rock mass along the borehole. This paper analyses 186 boreholes, drilled using a water powered in-the-hole (ITH) drilling technique considering drill parameters; penetration rate, rotation pressure, feed pressure and percussive pressure. In addition, it suggests, calculates and uses a parameter reflecting rock fracturing. Sixty-three of the holes were filmed with a borehole camera to reveal the geo-mechanical features. The results show that the responses from the drill monitoring system can distinguish between solid rock, fracture zones, cavities and damaged rock. The ability to extract this information directly from the drilling operation provides unique prior information and can be useful to adjust production planning before charging and blasting boreholes.

  • 5.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Development of a geological model for chargeability assessment of borehole using drill monitoring technique2018In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 109, p. 9-18Article in journal (Refereed)
    Abstract [en]

    In the mining industry, the ability to charge and blast a production borehole is fundamental. However, if rock mass conditions are challenging, with cavities, fracture zones or even unstable boreholes, the charging crew may fail to insert the required amount of explosives, resulting in bad fragmentation and significant production disturbances in the downstream process. Prior detailed knowledge of the chargeability of each production fan or ring will improve both the planning and execution of the charging work in a mine. The paper describes a study using the drill monitoring technique to assess the chargeability of production boreholes. For the study, data were collected on four drill parameters, penetration rate, rotation pressure, feed pressure and percussive pressure, from 23 drill fans with a total of 186 boreholes. A parameter called fracturing was calculated based on penetration rate variability and rotation pressure variability. Sixty-three boreholes were filmed to establish different rock mass conditions: solid rock, cavities, fractured zones and cave-ins. Principal Component Analysis (PCA) was performed to model the relationship between drill monitoring data and the geological features. The developed model shows high potential by identifying charging problems directly from drill monitoring data, and has been verified and validated in a real charging operation in an operating mine.

  • 6.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Development of a geo-mechanical model for chargeability assessment of borehole using drill monitoring techniqueIn: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545Article in journal (Refereed)
  • 7.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Zongxian
    LKAB, Research & Development, 983 81 Malmberget.
    An investigation of borehole stability in LKAB Malmberget underground mine, Sweden2013In: Rock Characterisation, Modelling and Engineering Design Methods -: Proceedings of the 3rd ISRM SINOROCK 2013 Symposium / [ed] Xia-Ting Feng; John A. Hudson; Fei Tan, Leiden: CRC Press/Balkema , 2013, p. 747-752Conference paper (Refereed)
    Abstract [en]

    Instability in production blast holes causes poor fragmentation, lower ore recovery, delay in production and higher costs in crushing and grinding. In this investigation, three large ore bodies named Alliansen, Fabian and Vi-Ri were selected. A video camera was used for mapping production blast holessoastofind borehole stability problems. A total of 298 blast holes were filmed. There were eight types of stability problems identified in the blast holes. These are shear zone, loose rock, cave, crack, deformation, stone jammed, spalling and rock breakage. Among these problems, deformation and crack were the most common ones in all the ore bodies. In addition, instability problem in the blast holes were higher around the rings which were blasted last. Further it has been found that the area which is affected by more seismic responses is the same as the one where several boreholes were re-drilled or sheared.

  • 8.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Monitoring of Drill System Behavior for Water-Powered in-the-hole (ITH) drilling2017In: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 7, no 7, article id 121Article in journal (Refereed)
    Abstract [en]

    A detailed understanding of the drilling system and the drilling control is required to correctly interpret rock mass conditions based on monitored drilling data. This paper analyses data from hydraulic in-the-hole (ITH) drills used in LKAB’s Malmberget mine in Sweden. Drill parameters, including penetration rate, percussive pressure, feed pressure, and rotation pressure, are monitored in underground production holes. Calculated parameters, penetration rate variability, rotation pressure variability, and fracturing are included in the analysis to improve the opportunity to predict rock mass conditions. Principal component analysis (PCA) is used to address non-linearity and variable interactions. The results show that the data contain pronounced hole length-dependent trends, both linear and step-wise linear, for most parameters. It is also suggested that monitoring can be an efficient way to optimize target values for drill parameters, as demonstrated for feed force. Finally, principal component analysis can be used to transfer a number of drill parameters into single components with a more straightforward geomechanical meaning

  • 9.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Evaluation of operating life length of rotary tricone bits using Measurement While Drilling data2016In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 83, p. 41-48Article in journal (Refereed)
  • 10.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Evaluation of Rock Mass Characteristics Using Measurement While Drilling in Boliden Minerals Aitik Copper Mine, Sweden2014In: Mine Planning and Equipment Selection: Proceedings of the 22nd MPES Conference, Dresden, Germany, 14th - 19th October 2013 / [ed] Carsten Drebenstedt; Raj Singhal, Encyclopedia of Global Archaeology/Springer Verlag, 2014, Vol. 1, p. 81-91Conference paper (Refereed)
    Abstract [en]

    In the mining industry, rock mass characterization is necessary for both short term and long term production planning, but it is a challenge to get detailed information on the geo-mechanical properties of rock mass. Measurement While Drilling (MWD) is a well-established technique to retrieve data on the mechanical response of the rock mass in penetrated horizons. With this data the mining process could be improved regarding drilling cycle time, blast design, loading, hauling, crushing energy and grinding energy for present and underlying benches. This paper presents an attempt to characterize the rock mass in Boliden Minerals Aitik Mine, the largest open pit copper mine of Europe, located in the Northern part of Sweden. Penetration rate and specific energy are used to describe how subsequent benches (upper and lower) are inter-related. The behavior of Specific Energy and Penetration Rate is further evaluated and analyzed.

  • 11.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    The use of specific energy in rotary drilling: the effect of operational parameters2015Conference paper (Refereed)
    Abstract [en]

    In rotary drilling, specific energy is considered to be an important parameter for defining mechanical efficiency of the rock destruction process. Specific Energy is defined as the energy required to remove one unit of rock. Specific energy is the function of the size of the borehole and various operational parameters including feed force, rotation speed, rotation torque and penetration rate. The harder the material, the higher the specific energy. The traditional method to calculate the specific energy is based on the parameters penetration rate, feed force, torque and rotation speed, that can be provided by Measurement While Drilling (MWD) data from the drill process. In this study, MWD data from an open pit mine in Sweden are used to evaluate data trends among logged parameters and calculated average specific energy. The results show that there is a significant hole length dependency for penetration rate and feed force that affects the predicted specific energy. This may be explained by that the hole cleaning efficiency is reduced with increasing hole length. The analysis shows that the specific energy is over-estimated by 45% in the bottom of an 18 m hole compared to the collaring point. The suggested solution is to use hole average or complement the specific energy calculation with a hole length related component.Keywords: Specific energy, Measurement While Drilling (MWD), Rotary drilling, Geo-mechanical response, Rock-destruction process

  • 12.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Zhang, Zongxian
    University Centre in Svalbard.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Borehole instability in Malmberget Underground Mine2015In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 48, no 4, p. 1731-1736Article in journal (Refereed)
  • 13.
    Gustafson, Anna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Bolting Procedures in Outokumpu’s Kemi Mine2014In: Mine Planning and Equipment Selection: Proceedings of the 22nd MPES Conference, Dresden, Germany, 14th – 19th October 2013 / [ed] Raj Singhal ; Carsten Drebenstedt, Encyclopedia of Global Archaeology/Springer Verlag, 2014, Vol. 3, p. 411-420Conference paper (Refereed)
    Abstract [en]

    The working environment for ground support installation in mines has improved a lot during the last 20-30 years, with more and more mechanized installations of the different ground support elements such as bolts, cable bolts and screen. However ground support installation productivity has not followed the same development curve. In fact, its productivity has more or less remained constant and in some cases has even fallen if, as an example, comparisons are made between the manual and mechanized installations of bolts. One reason for this is that modern mechanised bolt rigs are very complex, capable to perform many tasks. To be able to fully utilize this equipment’s capability a different level of maintenance and product support is required. This paper describes the bolting process in Outokumpu’s Kemi mine that has a very interesting procedure for bolt installation and has also paid an unsurpassed attention to the maintenance procedures to improve productivity.

  • 14.
    Navarro, Juan
    et al.
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Segarra, Pablo
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Johansson, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Sanchidrián, José Ángel
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Application of drill-monitoring for chargeability assessment in sublevel caving2019In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 119, p. 180-192Article in journal (Refereed)
    Abstract [en]

    Currently, the charging procedure for sublevel caving mining is carried out with no prior information of the rock mass condition. Thus, engineers are blindsided to unexpected rock conditions and ill-prepared to address issues associated with collapsing boreholes. This results on charging problems and, as consequence, bad fragmentation of the rock after blasting which difficult ore loading and transportation as the gravity flow of the rock is reduced.

    This paper builds up the work done by Ghosh et al. (IJRMMS, 2018), to classify the geotechnical rock condition into five classes (solid rock, fractured rock, cave-in, minor and major cavity). From it, two applications based on the Measure While Drilling (MWD) technique have been developed: one for geotechnical rock condition of orebodies and the other for predicting the risk of collapse in boreholes. The work of Ghosh et al. has been improved into a geotechnical rock condition block model to simplify the quantitative assessment and automatic recognition of rock trends. A thorough correction of the MWD parameters has been also applied to minimize external influences other than the rock mass. From it, the risk of borehole collapses model has been developed by comparing different combinations of the geotechnical rock condition block-model with the charging length of 102 production fan-holes. The assessment of the number of collapsed and non-collapsed blastholes and the charging length/blasthole length ratio has been used to assign high, medium or low risk of collapse to each combination. The results predict collapses in the first half of the fan-holes for the high risk, collapses in the second half of the fan-hole for the medium risk and no collapses along the hole for the non-risk holes. The two models have been applied in large scale for two orebodies in the Malmberget mine, Sweden, which comprises 20 drifts and 5060 fan shape long-holes.

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