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  • 1.
    Nilsson, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Current and historical monitoring data at the Kiirunavaara footwall: a review2014Rapport (Annet vitenskapelig)
    Abstract [en]

    This literature review covers the current and historical surface and underground monitoring systems. Available data from both active and decommissioned systems is collected and presented. The review also covers data retrieved through temporary measurements such as core-drilling, geological mapping and damage mapping. Geotechnical data is sorted by origin and type categorised as rock mass properties, joint set data or equivalent input data for numerical modelling. Measurement data is categorised by origin, observations, field measurements and laboratory data. The results from these geotechnical studies are summarized and referenced to the original publication and put into context to a large scale footwall failure.The study is concluded by a review of some of the previous numerical models covering the Kiirunavaara footwall. The review has found that during the last decade the numerical analyses related to the footwall have all used the same sets of data, all originally compiled and presented in 2001 and that the footwall rock mass has consistently been treated as a single coherent geological unit. Mohr-Coulomb failure models have been used throughout.

  • 2.
    Nilsson, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Damage mapping of footwall fracturing at the Kiirunavaara mine: underground mapping between levels 320 and 775 m2014Rapport (Annet vitenskapelig)
    Abstract [en]

    This document contains the results and analyses of a mapping campaign for the partial determination of the outer fracture line in the Kiirunavaara footwall conducted on 19-22 March 2013. As reference the levels 320, 420, 507, 540, 740 and 775 m have been used. Damage mapping has during this campaign been performed on all levels except level 420 m where previous mapping results were considered sufficient. The results from the mapping showed that the outer fracture line has been practically stationary on the shallow levels during the last years as new damage was only observed on the deeper levels. Damage on levels above 740 m was judged to be mainly controlled by naturally existing discontinuities. On levels below 740 m the majority of the failures seemed to be stress induced. The results have been used to interpolate damage lines along the respective levels which have then been used to estimate a continuous fracture surface between the studied levels. The fracture surface was analysed with respect to the geometrical shape and with some consideration to the position of the underground infrastructure. A simplified construction plane of the fracture surface could be stated as dipping 55-60˚ to the east and striking parallel to the ore contact. An extension of the construction plane towards the ground surface indicates a day-lighting line that lies significantly further into the footwall than surface cracks have been observed. Extension of the construction plane downwards was not recommended as the behaviour of the lowest mapped level (775) significantly deviates from the dip and strike indicated by the above lying observations.

  • 3.
    Nilsson, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Feasibility study on global footwall stability at the Kiirunavaara mine2012Rapport (Annet vitenskapelig)
    Abstract [en]

    This feasibility study was carried out over a time period of 6 months by Luleå University of Technology on request by, and in co-operation with, LKAB (Luossavaara Kiirunavaara Aktiebolag).This work reviews the documentation from previous studies including: descriptions of the geomechanical conditions, records of damage and fallouts in the footwall, installed measuring equipment and associated data, modelling attempts of the Kiruna mine as well as scientific publications. from the Chuquicamata, Cadia Hill, Bingham Canyon, Kvannevann, perseverance, Stobie, Ridgeway and Palabora mines. In addition, damage mapping has been carried out in relation to this work and the results are published as separate documents titled “Kartering av huvudnivå 775, 2012, Meddelande 12-20076” and “Kartering av nivåerna 230 – 775 m mellan Y22 – Y28, 2012, Meddelande 12-20077” respectively.The review suggests that the main host rock type in the footwall is a Precambrian aged tracho-andesite locally referred to as syenite porphyry. The syenite porphyry borders the ore and ore contact. The porphyry is replaced by competent granite as one moves westward away from the footwall on levels below 800 m. Documentation of the rock mass at a distance from the ore contact is limited to drift mapping. Information on dominant joint orientations is available for most levels in moderate detail. Dominant joint sets dipping parallel or sub parallel to the orebody are mapped on most levels.The assumed failure mode and mechanisms for the large scale footwall failure have changed as the mine deepened, the prognosis models have been continuously updated to fit observed damage.• 1970s – The outer fracture line was considered traceable using a linear failure surface dipping 50-60˚. (Kiviniemi I ,1977)• 1980s – The dip interval of the failure surface was narrowed to 55-60˚; this model was used into the early 90s. (Finn, 1981),(Dahner, 1990)• 1992 – New failure modes were assumed, the linear model was replaced by circular shear failure through the rock mass with the estimated values c≈1.5MPa φ =30˚(Dahner-Lindkvist, 1992-a)• 1993 – The cohesion value was somewhat confirmed as a parameter study by Hustrulid (1993) indicated that c was not allowed to exceed 2MPa for the failure surface to reasonably fit the observed damage. (Hustrulid,1993)• 1996 – The local footwall stability prognoses still used a linear failure line dipping 60˚ (Dahner-Lindkvist, 1996-c)• 2000 – The estimated strength parameters for the circular shear failure were updated to c≈0.6MPa φ =35˚ (Henry, 2000-a)The failures reported in the external case studies (when applicable) tend to progress relatively slowly and involve complex failure modes combining structurally controlled failure with failure through the rock mass. Problem descriptions and corresponding solutions directly transferrable to the experiences at the Kiirunavaara mine cannot be found in the referenced literature.The review have shown a few specific areas in which further research needed, these areas are primarily related to the behaviour of the caved rock masses, determination of the true failure mechanisms in the footwall and the development of new prognosis models for the future stability.The study is closed by the outline for continued research envisioned as a five year PhD-thesis project.

  • 4.
    Nilsson, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Edelbro, Catrin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Sharrock, Glenn
    University of New South Wales.
    Small scale joint surface roughness evaluation using digital photogrammetry2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a procedure on how photogrammetry by simple means can be used to create a joint surface profile using standard off-the-shelf equipment. The results are presented as a step by step instruction ranging from imaging of a rock sample to validation of the acquired data to preparation of a numerical model. Imaging is performed using a camera with a fixed lens in combination with the photogrammetry software 3DM CalibCam and 3DM Analyst. Surface data validation is carried out by means of laser scan in order to create a reference surface for local coordinate comparison to the photogrammetry data terrain model (DTM). The photogrammetry data is proven to be accurate on a scale smaller than one millimetre and a numerical shear-box model is prepared using the profiles as input. Surface evaluation show no clear indication that any part of the surface would be less accurately imaged due to directional bias as the areas of deviation are evenly spread across the sample. Profiles derived from photogrammetry are related to JRC. Calibration of the shear-box model is on-going; no numerical results are included in this paper.

  • 5.
    Nilsson, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Saiang, David
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Fracturing in the footwall at the Kiirunavaara mine, Sweden2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Kiirunavaara mine is a large scale sub level caving (SLC) mine located near the city of Kiruna in northern Sweden. It is owned and operated by LKAB (Luossavaara-Kiirunavaara AB). The mine produces approximately 28 million tonnes of iron ore annually. Over the last 30 years the mine has experienced a slow but progressive fracturing and movement in the footwall rock mass induced by the SLC operations. The footwall contact which assumes a “slope-like” geometry is partially supported by the caved material from the hangingwall. However, since the late 1980s damage has been observed on the footwall crest as well as within the footwall. Progressive rock mass movement in the footwall is indicated by surface subsidence and visual observations underground. The extent of the damage has traditionally been estimated using empirical relations. Most of the current long term underground infrastructure within the footwall is located at a considerable distance from the ore contact. However, for new developments on deeper levels it is imperative to predict the future extent of the damage volume. Approximating the position of the damage boundary in the footwall at the current state of mining would assist in predicting the extent and characteristics of the damage volume as the mine deepens. LKAB and LTU (Lulea University of Technology) have therefore initiated a joint research project to study the long term stability of the footwall at the Kiirunavaara mine. This paper constitutes part of the work in this research.The paper describes a damage mapping campaign and subsequent analysis of the Kiirunavaara mine footwall to approximate the outer boundary of the damage. The footwall was systematically mapped on 6 levels between 320 and 800 m. The mapping results were then used to interpolate damage lines on the respective levels. The damage lines were used to construct a continuous damage surface between the studied levels. Existing records of damage mapping, monitoring and predictions were reviewed and compared to the results from the current campaign. The new results show that, the outer damage surface appears to remain stationary on the upper levels while new damage was observed on the deeper levels. At levels above 740 m the damage is judged to be mainly controlled by movements along natural discontinuities. At levels below 740 m the majority of the damage seems to be stress induced.

  • 6.
    Svartsjaern, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Itasca Consultants AB Luleå .
    A Prognosis Methodology for Underground Infrastructure Damage in Sublevel Cave Mining2019Inngår i: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, nr 1, s. 247-263Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In sublevel caving (SLC), the caving of the hangingwall due to ore extraction emphasises placement of the mining infrastructure in the footwall. While the footwall in general is less affected by ground settlement compared to the hangingwall, the changes in stress field from mining are significant. The footwall infrastructure must thus be positioned sufficiently far into the footwall to avoid damage from the mining-induced stress; however, placing the infrastructure farther into the footwall increases costs associated with additional drifting and operational distances. This paper presents a case study in which a robust prognosis tool for predicting infrastructure damage associated with SLC mining is developed. The concept of the proposed methodology was developed for the Luossavaara-Kiirunavaara Aktiebolag Kiirunavaara SLC mine. Initial steps are data collection through systematic damage mapping followed by conceptual modelling of the general rock mass response to mining. The results of the conceptual models are used as the basis for refined calibrated models detailing the damage development and failure mechanisms. The main system behaviour, failure mechanism and associated damage evolution are incorporated into a bilinear equation using the studied depth and local ore width as input to estimate the final horizontal damage extent from the footwall contact after mining of any specific level. The proposed relationship accurately replicates the current damage pattern within 40 m for more than 70% of the recorded observations up until current mining. The anticipated future damage extent is also shown to be well correlated with current micro-seismic event locations. The connection between seismic rock mass damage and subsequent infrastructure damage during de-confinement suggests that current seismic records from operations, which currently experience no stability issues, might become important at later mining stages.

  • 7.
    Svartsjaern, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Footwall stability in SLC mining2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is based on a case study of the Kiirunavaara sublevel cave (SLC) mine. It focuses on footwall stability and damage development in the mining infrastructure on mine scale. Damage to the infrastructure is mappable for the full height of the footwall by access through decommissioned infrastructure associated with earlier mining stages. Damages range from pure structurally controlled failures (wedge failures) in the upper part of the footwall to fracture growth through intact rock combined with micro‑seismic emissions at the active mining depth.

    The thesis addresses four distinct research questions;

    (i) What are the predominant failure mechanisms for the Kiirunavaara footwall?

    (ii) What is the role of confinement on the damage development in the footwall?

    (iii) How does the SLC relate to the footwall damage development?

    (iv) How can infrastructure damage associated to the future mining be estimated using currently available data?

    Two sets of calibrated numerical models were used to study the damage evolution processes using damage mapping data as the main calibration parameter. Validation of the models was achieved by correlation of model output to micro-seismic locations. The modelling and damage mapping results were used as the basis for the development of a simple prognosis tool for estimating the ultimate extent of infrastructure damage associated to the mining advance for future mining steps.

    A literature review on slope failure modes, large scale failures in cave mining and failure tracking using micro-seismic locations is included to provide background and definitions. The literature describes principal failure modes as well as mechanism combinations such as structurally controlled failures initiated by deep seated rock mass failures or relaxation. Cases are presented where previously stable structures become destabilised by cave advance and examples where micro‑seismic recordings were used to track deformations and the initiation and growth of newly formed fractures.

    The Kiirunavaara SLC mine is presented in detail as the main case study of the work. The mine has been in operation since the early 20th century with a transition to underground operation over 50 years ago. The extent of the orebody is 4 km in length with an average width of 80-90 m, the termination at depth has yet to be determined. The ore has an average dip of 60˚ east and a dip-along-strike to the north. Both the footwall and hangingwall rock masses are considered hard and competent with UCS values for the footwall ranging from ca. 130 MPa to extreme cases of 600 MPa. The ore is mined in production blocks about 400 m wide (along strike), Mining of the northernmost blocks, situated in the Lake ore, did not start as open pit operations but has been accessed from the underground via SLC only.

    The instabilities in the footwall has been addressed by several research studies in the past, with the predominant failure mechanisms in different studies being suggested as large scale tensile failure, complex wedge failure, or rotational shear failure, i.e., some type of principal slope failure.

    In this work, conceptual numerical models in UDEC were calibrated to fit underground damage mapping data by tracking numerical shear strain concentrations. The conceptual models suggested rock mass damage without the indications of development of large scale slope failure mechanisms such as shear bands. Mine scale PFC models were calibrated with respect to the rock mass strength parameters derived by the conceptual UDEC models and used to study rock mass fracturing in the absence of large scale failure. It is shown that damage to the rock mass occurs mainly close to the active mining in a seismically active zone. This is suggested to weaken and soften the rock mass to allow the development of infrastructure damage in this volume to occur as the rock mass relaxes when entering the stress shadow of the SLC as mining progresses.

    The damage to the rock mass at the production depth is argued, based on seismic records and a parametric study in UDEC, to constitute of large quantities of local shear failures coalescing to appear as a large scale step-path or rotational shear failure in mapping records. The extent of the associated infrastructure damage is predicated to be limited by the extent of the damaged rock mass zone. A simple bi-linear equation is suggested using ore-width and mining depth as input to estimate the ultimate extent of the damaged zone for each mining stage and thus the limit of later infrastructure damage development.

    The thesis is concluded with recommendations for future work and potential for continued research.

  • 8.
    Svartsjaern, Mikael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Predominant failure mechanisms at the Kiirunavaara mine footwall2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Luossavaara-Kiirunavaara Aktiebolag (LKAB) Kiirunavaara mine is a large scale sub-level caving (SLC) mine in northern Sweden. The use of SLC as a mining method inherently causes significant rock mass movements above the extraction level. It has been one of the objectives of LKAB since the early 1990s to accurately forecast the global stability of the footwall in relation to the inherent rock mass movements from the sub-level caving. In the Kiirunavaara case, the dip of the main ore-body entails the footwall to develop as a rockslope confined by cave material from the hangingwall. It has been discussed that the global stability of the footwall is likely related to the interaction of two or more failure mechanisms acting in combination, however, the true footwall failuremechanisms are still debated. The objective of this thesis is to study and evaluate the footwall behaviour and determine the predominant mechanisms by combining data from field observations, numerical modelling and seismic data analysis. Field data was collected through damage mapping on decommissioned levels in the footwall on depths between 120 to 700 m for the full 4 km ore-body length. From the mapping data a conceptual boundary between damaged and undamaged footwall rock was established in the form of a damage boundary surface. The 3D geometry of the damage surface was analysed and a section was extracted and used in calibrating numerical models for simulatingthe footwall behaviour in response to mining. A parametric study was performed to highlight high impact inputs and study plausible origins of the conceptual damage surface. A base case model was adopted to explain the failure evolution and used in the analysis of seismic data. The seismic data was analysed with respect to origin mechanisms as well as temporal and spatial location patterns. The outline of the large scale footwall fracturing interpreted from the conceptual damage surface was geometrically complex. No single principal failure modes could be identified from evaluating the 3D geometry favouring the initial assumption of multiple mechanism interactions. In addition, the mapping data itself indicated changes in failure mode with respect to depth. On higher levels structurally controlled damages were predominant while general rock mass failures became common on lower levels. The parametric study related thehighest influence on plastic response to the internal cohesion followed by internal friction angle. This was interpreted for the base case as the rock mass being more sensitive to shear failures in favour of tensile failures. This indication was further strengthened by the evaluation of the seismic data. The origin analysis of the seismic events pointed to a significant dominance of shear origin events clustered in active fracturing volume indicated by the base case numerical analysis. By combining field observations, numerical modelling and seismic analysis a plausible description of the large scale footwall fracturing could be provided. The structurally controlled failures in the upper and mid portion of the footwall are reactions to active failure on deeper lying levels. Active fracturing of the footwall rock mass occurs based on the numerical and seismic results on levels on and underneath the current mining level. On the levels where active fracturing takes place the rock mass is confined by the support pressurefrom the un-mined ore-body. As mining progresses deeper the confinement is lowered as the ore is replaced by low stiffness cave rock. Due to the loss of support pressure the rock mass expands towards the sub-level cave and the induced weaknesses are activated and manifested as drift damage during rock mass mobilisation. The numerical models showed that the mobilised rock mass above the mining level exhibits the displacement pattern of a potential curved shear failure. This failure path intersects both the footwall slope face and thestructures from the upper footwall and thus enables these structures to shear.

  • 9.
    Svartsjaern, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Eitzenberger, Andreas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Determination of magnitude completeness from convex Gutenberg-Richter graphs in the central portion ofthe Kiirunavaara mine2017Inngår i: The Southern African Journal of Mining and Metallurgy, ISSN 2225-6253, E-ISSN 1543-9518, Vol. 117, nr 6, s. 545-560Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes a study of seismic records from the Kiirunavaaramine footwall which were interpreted in relation with numerical modelsdeveloped outside the study. Seismic data was retrieved from a portion ofthe mine and filtered with respect to the ratio between energy carried byan event's P (primary) and S (secondary) waves (Es/Ep ratio), localmagnitude, and active mining depth. The data was analysed using Es/Epratios and Gutenberg-Richter graphs to determine the event origin,mechanisms, and minimum magnitude cut-off. The magnitudecompleteness was identified by studying the b-value stability and b-valuedifferentiation between origin sets. It was shown that, by separatingseismic events into the origin components shear, complex, and tensilebased on Es/Ep ratios, a representative value for the magnitudecompleteness can be identified for a catalogue with a convex cumulativelog curve. The majority of the events were shown to be of shear-slip originbased on the recorded Es/Ep ratios, with pure tensile events constitutingonly about 10% of the recorded data. Spatial and temporal event locationpatterns were studied and compared with numerical modelling results. Thecomparison showed a correlation between shear-slip seismic events andvolumes experiencing high differential stresses in the lower part of thefootwall. In the upper part of the footwall the results did not reveal anyclear correlation between observed damage in drifts and seismic eventlocations. The concentration of seismic events in the lower portion of thefootwall is discussed in the context of rock mass displacements. Theresults indicate a possible connection between mine seismicity at depthand damage observations in the drifts in higher non-seismic areas byseismic softening and subsequent lateral expansion of the rock mass.

  • 10.
    Svartsjaern, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Saiang, David
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Discrete Element Modelling of Footwall Rock Mass Damage Induced by Sub-Level Caving at the Kiirunavaara Mine2017Inngår i: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 7, nr 7, artikkel-id 109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Kiirunavaara mine is one of the largest sub-level-caving (SLC) mines in the worldand has been in underground operation for more than 50 years. The mine has been the focus ofseveral case studies over the years. The previous works have either focused on the caving of thehanging wall, using the footwall as a passive support, or focused on the footwall using the hangingwall to apply a passive load. In this updated study the findings of the previous case studies arecombined to study the interaction between the caving hanging wall, the developing cave rock zoneand the footwall. The geological data for the rock types in the mine area are used to derive upperand lower limits for the geomechanical parameters calibrated for numerical models in the previousstudies. The calibrated parameters are used as inputs to a numerical model constructed usingItasca’s Particle-flow-code (PFC) encompassing a mine-scale 2D section at the mid portion of themine. The model captures the failure locations well in the footwall underground and indicatesdamage development without a coherent large-scale failure. The trend in subsidence data on thehanging wall is adequately simulated but the magnitude of deformation is underestimated. Theinput strength for the hanging wall was lowered to study the impact of hanging wall strength onfootwall damage development. It is shown that when the footwall strength is kept constant, whilelowering the hanging wall strength, the extent of damage and magnitude of displacements in thefootwall increases. From these observations it is argued that the hanging wall and footwall cannotbe studied independently for the Kiirunavaara mine since the cave rock zone significantly affectsthe damage development in both walls.

  • 11.
    Svartsjaern, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Saiang, David
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Mäkitaavola, Karola
    Loussavaara-Kiirunavaara Limited, Lulea.
    Underground Footwall Monitoring at the Sublevel Caving Mine – Kiirunavaara, Sweden2016Inngår i: Seventh International Conference & Exhibition on Mass Mining: (MassMin 2016), Sydney: The Australian Institute of Mining and Metallurgy , 2016, s. 773-780Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Kiirunavaara mine is a large-scale (28 Mt per annum) iron ore mine located in northern Sweden. The mine is owned and operated by Luossavaara-Kiirunavaara Aktiebolag (LKAB) using sublevel caving (SLC). The SLC area underlies an open pit decommissioned in the 1950s, the current main SLC haulage level is situated at an depth of 1100 m. The main orebody dips 60 degrees to the east with a distinct boundary defining the hanging wall to the east and footwall to the west. Since the 1980s damage has been observed both in the footwall rock mass as well as on the footwall crest of the open pit. Recent investigations indicate that the underground footwall damage is primarily controlled by large-scale slope failure mechanisms. Structurally controlled near-vertical planar shear failures in the upper footwall appear to be driven or facilitated by a step-path like curved shear failure situated in a zone starting ca 250 m, and intersecting the SLC about 100 m above the active mining level. To confirm this failure evolution a pilot underground measuring system has been designed and installed to monitor the expected rock mass displacements indicated by numerical models based on the above mechanisms. The systems consists of 50 m time domain reflectometry (TDR) coaxial cables installed in the footwall both across and away from an estimated damage extent boundary to monitor shear movements along natural joint surfaces. The TDR installation is combined with long extensometers to facilitate differentiation between diffuse shear and rock mass normal expansion. Additionally, a low-tech system of tape extensometer lines are installed in drifts and stopes running perpendicular to the ore strike to monitor horizontal displacements in the infrastructure as the footwall ‘slope’ loses confinement during mining advance when the mined out areas are replaced by caved rock from the hanging wall.

  • 12.
    Svartsjaern, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Saiang, David
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Eitzenberger, Andreas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Conceptual Numerical Modeling of Large-Scale Footwall Behavior at the Kiirunavaara Mine, and Implications for Deformation Monitoring2016Inngår i: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, nr 3, s. 943-960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Over the last 30 years the Kiirunavaara mine has experienced a slow but progressive fracturing and movement in the footwall rock mass which is directly related to the sublevel caving (SLC) method utilized by Luossavaara-Kiirunavaara Aktiebolag (LKAB). As part of an on-going work, this paper focuses on describing and explaining a likely evolution path of large-scale fracturing in the Kiirunavaara footwall. The trace of this fracturing was based on a series of damage mapping campaigns carried out over the last two years, accompanied by numerical modelling. Data collected from the damage mapping between mine levels 320 and 907 m was used to create a 3D surface representing a conceptual boundary for the extent of the damaged volume. The extent boundary surface was used as the basis for calibrating conceptual numerical models created in UDEC. The mapping data, in combination with the numerical models, indicated a plausible evolution path of the footwall fracturing that was subsequently described. Between levels 320 and 740 m the extent of fracturing into the footwall appears to be controlled by natural pre-existing discontinuities, while below 740 m there are indications of a curved shear or step-path failure. The step-path is hypothesised to be activated by rock mass heave into the SLC zone above the current extraction level. Above the 320 m level the fracturing seems to intersect a sub-vertical structure that daylights in the old open pit slope. Identification of these probable damage mechanisms was an important step in order to determine the requirements for a monitoring system for tracking footwall damage. This paper describes the background work for design of the system currently being installed.

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