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Svartsjaern, M. & Eitzenberger, A. (2017). Determination of magnitude completeness from convex Gutenberg-Richter graphs in the central portion ofthe Kiirunavaara mine. The Southern African Journal of Mining and Metallurgy, 117(6), 545-560
Open this publication in new window or tab >>Determination of magnitude completeness from convex Gutenberg-Richter graphs in the central portion ofthe Kiirunavaara mine
2017 (English)In: The Southern African Journal of Mining and Metallurgy, ISSN 2225-6253, E-ISSN 1543-9518, Vol. 117, no 6, p. 545-560Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
South African Institute of Mining and Metallurgy, 2017
National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-64636 (URN)10.17159/2411-9717/2017/v117n6a5 (DOI)000406202900005 ()
Note

Validerad;2017;Nivå 2;2017-07-06 (andbra)

Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2019-02-18Bibliographically approved
Svartsjaern, M. & Saiang, D. (2017). Discrete Element Modelling of Footwall Rock Mass Damage Induced by Sub-Level Caving at the Kiirunavaara Mine. Minerals, 7(7), Article ID 109.
Open this publication in new window or tab >>Discrete Element Modelling of Footwall Rock Mass Damage Induced by Sub-Level Caving at the Kiirunavaara Mine
2017 (English)In: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 7, no 7, article id 109Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2017
National Category
Mineral and Mine Engineering Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-64484 (URN)10.3390/min7070109 (DOI)000407363800003 ()2-s2.0-85021436574 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-07-06 (andbra)

Available from: 2017-06-26 Created: 2017-06-26 Last updated: 2018-07-10Bibliographically approved
Svartsjaern, M. (2017). Footwall stability in SLC mining. (Doctoral dissertation). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Footwall stability in SLC mining
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Abstract [sv]

Denna avhandling baseras på en fallstudie av skivrasgruvan Kiirunavaara. Fokus ligger på liggväggstabilitet och skadeutveckling på gruvans infrastruktur i gruvskala. Infrastrukturskador kan karteras längs med hela liggväggens höjd där tillgång till bergmassan ges via urdrifttagna ortar och ramper drivna i samband med tidigare brytningssteg. Dokumenterade skador varierar med djupet – från strukturstyrda brott i den övre delen av liggväggen till ny sprickbildning genom intakt berg kombinerat med mikro-seismik vid nuvarande brytningsdjup.

Fyra distinkta forskningsfrågor avhandlas;

(i) Vilka är de dominerande brottsmekanismerna i Kiirunavaaras liggvägg?

(ii) Vilken roll spelar inspänning för brottsutvecklingen i liggväggen?

(iii) På vilket sätt relateras skivrasbrytningen till brottsutvecklingen?

(iv) Hur kan skador på gruvans infrastruktur kopplat till framtida brytningssteg uppskattas med data tillgängliga idag?

Två omgångar med kalibrerade numeriska modeller togs fram för att studera skadeutvecklingen i liggväggen med skadekarteringsdata som primär kalibreringsparameter. Validering av modellerna uppnåddes genom att studera samstämmigheten mellan modellresultaten och lokaliseringen av mikro-seismiska händelser. Modellresultaten och skadekarteringsdatabasen användes som grund för att utveckla ett enkelt prognosverktyg för att uppskatta den slutgiltiga utbredningen av infrastrukturskador direkt associerade med gruvbrytningen för framtida brytningssteg.

En litteraturstudie av släntbrott, storkskaliga brott i samband med rasbrytning samt brottsövervakning med mikro-seismik är inkluderad som bakgrund och för att definiera terminologier som används genom avhandlingen. Literaturstudien beskriver principiella brottsmekanismer samt kombinationer av mekanismer såsom strukturstyrda brott pådrivna av djupt belägna bergmassebrott eller minskad inspänning. Fallstudier presenteras där tidigare stabila strukturer destabiliseras av rasbrytningens framskridande och exempel där mikro-seismikdata använts för att följa deformationer samt initiering och tillväxt av nya sprickor i intakt berg och bergmassa.

Kiirunavaaragruvan presenteras i detalj som den huvudsakliga fallstudien för arbetet. Gruvan har varit aktiv sedan tidigt 1900-tal med övergång till underjordsbrytning för över 50 år sedan. Malmkroppens utbredning är 4 km längs strykningen med en genomsnittlig vidd av 80-90 m, och malmkroppens fortsättning mot djupet är öppen. Malmen har en genomsnittlig stupning av 60 grader öst med en fältstupning mot norr. Bergmassan i både liggvägg och hängvägg anses vara hård och kompetent med UCS värden för liggväggen mellan ca. 130 MPa till extrema fall av 600 MPa. Malmen bryts i produktionsblock med ca 400 m bredd (längs malmens strykning). Brytning av de nordligaste blocken, belägna i Sjömalmen, har inte skett i dagbrott utan har utförts enbart via skivrasbrytning.

Instabiliteten i liggväggen har avhandlats i ett flertal tidigare studier. De dominerande brottsmekanismerna har föreslagits i tidigare arbeten som storskaligt dragbrott, komplext kilbrott eller cirkulärt skjuvbrott d.v.s. någon typ av principiellt släntbrott.

I arbetet för denna avhandling kalibrerades konceptuella numeriska modeller i UDEC mot skadekarteringsdata från liggvägens underjord, med avseende på koncentrationer av skjuvtöjningar. De konceptuella modellerna visade på bergmasseskador utan indikationer på storskaligt släntbrott, exempelvis koncentrationer av numeriska skjuvband. PFC-modeller i gruvskala kalibrerades gentemot bergmasseparametrarna från de konceptuella studierna i UDEC för att direkt studera upprickningen av bergmassan i frånvaro av storskaliga brottsindikationer. Modellerna visade på att skador i bergmassan främst uppkommer nära brytningsområdet i en seismiskt aktiv zon. Detta föreslås försvaga och mjukgöra bergmassan vilket i sin tur leder till utveklingen av infrastrukturskador i den skadade volymen när berget avlastas då området hamnar i spänningsskugga från skivraset.

Ovanstående studier visar att skadorna som uppkommer i bergmassan, baserat på de konceptuella UDEC-modellerna och mikro-seismiska data, består av ett stort antal lokala skjuvbrott vilka samverkar till att framstå som ett storskaligt trappstegsbrott eller cirkulärt skjuvbrott i skadekarteringsdatat. Utbredningen av de relaterade infrastrukturskadorna förutspås begränsas av utbredningen av bergmasseskadorna uppkomna vid bryningen. Ett enkelt bi-linjär samband föreslås vilket använder malmbredd och brytningsdjup för att uppskatta den slutgiltiga utbredningen av skadezonen i bergmassan för varje brytningssteg, och i förlängningen begräsningen av senare uppkommande infrastrukturskador.

Avhandlingen avslutas med rekommendationer för fortsatt arbete samt framtida forskningspotential.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-65420 (URN)978-91-7583-949-3 (ISBN)978-91-7583-950-9 (ISBN)
Public defence
2017-10-27, F1031, LTU, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-11-24Bibliographically approved
Svartsjaern, M., Saiang, D., Nordlund, E. & Eitzenberger, A. (2016). Conceptual Numerical Modeling of Large-Scale Footwall Behavior at the Kiirunavaara Mine, and Implications for Deformation Monitoring (ed.). Paper presented at . Rock Mechanics and Rock Engineering, 49(3), 943-960
Open this publication in new window or tab >>Conceptual Numerical Modeling of Large-Scale Footwall Behavior at the Kiirunavaara Mine, and Implications for Deformation Monitoring
2016 (English)In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, no 3, p. 943-960Article in journal (Refereed) Published
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.

National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-10894 (URN)10.1007/s00603-015-0750-x (DOI)000371313300014 ()2-s2.0-84959154826 (Scopus ID)9c57e456-e493-4fed-a105-98f1373c0678 (Local ID)9c57e456-e493-4fed-a105-98f1373c0678 (Archive number)9c57e456-e493-4fed-a105-98f1373c0678 (OAI)
Note
Validerad; 2016; Nivå 2; 20150527 (miknil)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Svartsjaern, M., Saiang, D. & Mäkitaavola, K. (2016). Underground Footwall Monitoring at the Sublevel Caving Mine – Kiirunavaara, Sweden (ed.). In: (Ed.), (Ed.), Seventh International Conference & Exhibition on Mass Mining: (MassMin 2016). Paper presented at International Conference & Exhibition on Mass Mining : 09/05/2016 - 11/05/2016 (pp. 773-780). Sydney: The Australian Institute of Mining and Metallurgy
Open this publication in new window or tab >>Underground Footwall Monitoring at the Sublevel Caving Mine – Kiirunavaara, Sweden
2016 (English)In: Seventh International Conference & Exhibition on Mass Mining: (MassMin 2016), Sydney: The Australian Institute of Mining and Metallurgy , 2016, p. 773-780Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Sydney: The Australian Institute of Mining and Metallurgy, 2016
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-29284 (URN)2b4bf3f0-1153-45c7-861c-0a434e8324ad (Local ID)9781925100433 (ISBN)2b4bf3f0-1153-45c7-861c-0a434e8324ad (Archive number)2b4bf3f0-1153-45c7-861c-0a434e8324ad (OAI)
Conference
International Conference & Exhibition on Mass Mining : 09/05/2016 - 11/05/2016
Note
Godkänd; 2016; 20160401 (miknil)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-04-16Bibliographically approved
Svartsjaern, M. (2015). Predominant failure mechanisms at the Kiirunavaara mine footwall (ed.). (Licentiate dissertation). Paper presented at . : Luleå tekniska universitet
Open this publication in new window or tab >>Predominant failure mechanisms at the Kiirunavaara mine footwall
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
Predominant failure mechanisms at the Kiirunavaara mine footwall
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.

Place, publisher, year, edition, pages
Luleå tekniska universitet, 2015
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-18459 (URN)8b8661b3-b13c-486e-ba16-feea5d3d0221 (Local ID)978-91-7583-236-4 (ISBN)978-91-7583-237-1 (ISBN)8b8661b3-b13c-486e-ba16-feea5d3d0221 (Archive number)8b8661b3-b13c-486e-ba16-feea5d3d0221 (OAI)
Note
Godkänd; 2015; 20150119 (miknil); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Mikael Svartsjaern Ämne: Gruv- och Berganläggningsteknik/Mining and Rock Engineering Uppsats: Predominant Failure Mechanisms at the Kiirunavaara Mine Footwall Examinator: Bitr Professor David Saiang, Institutionen för samhällsbyggnad och naturresurser Luleå tekniska universitet Diskutant: PhD Diego Mars Ivars, Itasca Consulting Sweden AB, Kista Tid: Fredag den 27 mars 2015 kl 10.00 Plats: A1545, Luleå tekniska universitetAvailable from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Nilsson, M. (2014). Current and historical monitoring data at the Kiirunavaara footwall: a review (ed.). Paper presented at . : LKAB
Open this publication in new window or tab >>Current and historical monitoring data at the Kiirunavaara footwall: a review
2014 (English)Report (Other academic)
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.

Place, publisher, year, edition, pages
LKAB, 2014. p. 39
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-23319 (URN)67bd5c58-21ed-4349-8baf-1b3a77d3971a (Local ID)67bd5c58-21ed-4349-8baf-1b3a77d3971a (Archive number)67bd5c58-21ed-4349-8baf-1b3a77d3971a (OAI)
Note
Godkänd; 2014; 20140912 (miknil)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Nilsson, M. (2014). Damage mapping of footwall fracturing at the Kiirunavaara mine: underground mapping between levels 320 and 775 m (ed.). Paper presented at . : LKAB
Open this publication in new window or tab >>Damage mapping of footwall fracturing at the Kiirunavaara mine: underground mapping between levels 320 and 775 m
2014 (English)Report (Other academic)
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.

Place, publisher, year, edition, pages
LKAB, 2014. p. 27
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-24862 (URN)ccd724b7-c0c0-4200-97bf-4f978ca880b6 (Local ID)ccd724b7-c0c0-4200-97bf-4f978ca880b6 (Archive number)ccd724b7-c0c0-4200-97bf-4f978ca880b6 (OAI)
Note
Godkänd; 2014; 20140908 (miknil)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Nilsson, M., Saiang, D. & Nordlund, E. (2014). Fracturing in the footwall at the Kiirunavaara mine, Sweden (ed.). Paper presented at International Symposium on Block and Sublevel Caving : Mass Mining Projects and Knowledge For the Future 05/06/2014 - 06/06/2014. Paper presented at International Symposium on Block and Sublevel Caving : Mass Mining Projects and Knowledge For the Future 05/06/2014 - 06/06/2014.
Open this publication in new window or tab >>Fracturing in the footwall at the Kiirunavaara mine, Sweden
2014 (English)Conference paper, Oral presentation only (Refereed)
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.

National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-37434 (URN)b75786e0-7891-4564-92ac-b88a359480f9 (Local ID)b75786e0-7891-4564-92ac-b88a359480f9 (Archive number)b75786e0-7891-4564-92ac-b88a359480f9 (OAI)
Conference
International Symposium on Block and Sublevel Caving : Mass Mining Projects and Knowledge For the Future 05/06/2014 - 06/06/2014
Note
Godkänd; 2014; 20140610 (miknil)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-04-16Bibliographically approved
Nilsson, M. (2012). Feasibility study on global footwall stability at the Kiirunavaara mine (ed.). Paper presented at . : LKAB
Open this publication in new window or tab >>Feasibility study on global footwall stability at the Kiirunavaara mine
2012 (English)Report (Other academic)
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.

Place, publisher, year, edition, pages
LKAB, 2012. p. 137
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-24336 (URN)a8db3a96-116a-4cc6-8642-65f614b626e9 (Local ID)a8db3a96-116a-4cc6-8642-65f614b626e9 (Archive number)a8db3a96-116a-4cc6-8642-65f614b626e9 (OAI)
Note
Godkänd; 2012; 20130807 (miknil)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4189-945x

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