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Listening to the story of the rock mass: The integration of conventional and unconventional data to understand rock mass behaviour at the Kiirunavaara Mine
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0002-9175-7038
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The need to understand rock mass behaviour has never been greater; as mining globally progresses deeper to extract the precious resources humankind needs to maintain and forward our lives, we encounter rock behaviours associated with deep mining. These environments typically experience seismicity (including fault slip), rock bursting, strain bursting, spalling, aseismic movement along pre-existing discontinuities, and ground falls. These behaviours can have significant consequences to an operation’s safety and profitability. An understanding of the rock mass enables risk mitigating design.

However, a number of hindrances exist along the path to gaining this understanding. Limited information in the literature is available on which data to collect, the most appropriate analysis techniques, and how one combines varied data sources into a mine-scale understanding of the rock mass. In essence, we do not yet understand how to listen to the story of the rock mass. This thesis explores these research topics and develops and extends techniques and methodologies to address these issues. Data from Luossavaara-Kiirunavaara AB’s (LKAB) Kiirunavaara Mine was used, however a strong focus was given to developing general methodologies that can be applied to many mining environments.

The typical situation at most mine sites is one where many forms of data exist, a subset of which is conventional rock mechanics data. These data typically include, for example, laboratory testing for strength and stiffness of geological units, rock mass characterization from underground mapping, geological and geomechanical core logging, and positions and orientations of mapped discontinuities from underground mapping and/or oriented core logging. These data are often used for empirical design. It is common with particularly damaging seismic and/or ground fall events that additional data be acquired from underground damage mapping, but this information is rarely used on a larger scale. However, there is a subset of data that tends to be overlooked from a geomechanical perspective, even though the potential exists that this data can give us information about the characteristics of the rock mass. In the case of the Kiirunavaara Mine, this includes seismic data (including tomographic velocity structure), a database of information regarding ground falls, and laser imaging data.

A variety of conventional and unconventional data from the Kiirunavaara Mine were analysed using existing, and extensions of existing, analysis techniques. A 3-D geomechanical model was developed, incorporating geological and geomechanical core logging data, underground mapping data, and laboratory testing data. The resulting mine-scale model showed some particularly interesting results, including 1) a very large variation in intact rock strength within each statistical grouping of geological units, combined with much overlap between the strengths of geological units, and 2) a 3-D model of volumes of clay alteration built on geological core logging data calibrated favourably to data of underground mapping of clay. Unconventional data sources were also analysed, in particular the use of behavioural data to infer characteristics of the rock mass. Spatial and temporal patterns of ground falls were evaluated, alongside spatial patterns in overbreak, which were identified using new, mine-scale analysis techniques of laser scanning data.

Interestingly, correlations were apparent when comparing the analyses of distinct and separate data sources. Ground falls were concentrated in the intact rock between the clay volumes. The rock quality designation (RQD) had lower values in the same volume. Seismicity in the area was concentrated in the intact rock, with very few events in the clay volumes. 3-D velocity tomography models (developed by another researcher within this project) showed 1) no correlation with the RQD model (this result may highlight a limitation of scaling RQD data beyond it’s intended use), and 2) possible correlation with the clay volumes.

A methodology was developed using numerical stress analysis to identify, at an early stage of investigation, if a volumetric feature is of significance to seismic rock mass behaviour. With so much surmounting evidence that the clay volumes influence rock mass behaviour at the Kiirunavaara Mine, this feature was well-suited to be tested. Results showed that the clay volumes: 1) influence the mine-scale stress field, 2) have the potential to extend the volume of the rock mass which is expected to experience crack initiation (one underlying cause of seismicity), and 3) result in a stress field that enables slip along many of the orientations of mapped discontinuities (another underlying cause of seismicity).

Particularly valuable data were found to share the following characteristics: 3-D coverage, mine-scale, long-term, and multiple and distinct sources. It was important that the different data sources and their analyses led to the same conclusions even though they were separate and distinct. Unconventional data sources that were of particular use in this case include: spatial and temporal ground fall patterns and spatial patterns of seismicity. With further research, other unconventional data sources may show their value to rock mechanics analyses, such as spatial and temporal patterns of: seismicity, focal plane solutions from moment tensors, seismic stress inversion from moment tensors, overbreak, and possibly even tomography (the lack of strong correlation in this case may be specific to this environment and models used). Opening our minds to the possibilities, collaboration with experts in other fields, and a little creativity in our approach will help us in our quest to understand the stories of rock masses.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 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: urn:nbn:se:ltu:diva-65438ISBN: 978-91-7583-959-2 (print)ISBN: 978-91-7583-960-8 (electronic)OAI: oai:DiVA.org:ltu-65438DiVA, id: diva2:1140135
Public defence
2017-11-06, A1547, Luleå Tekniska Universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2017-11-24Bibliographically approved
List of papers
1. Modelling methodology: Structural geology and rock mass behaviour at Kiirunavaara Mine
Open this publication in new window or tab >>Modelling methodology: Structural geology and rock mass behaviour at Kiirunavaara Mine
2014 (English)In: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses / [ed] R. Alejano, Leiden: CRC Press, 2014, p. 643-648Conference paper, Published paper (Refereed)
Abstract [en]

Mining induced seismicity and rockbursting significantly increased in the LKAB Kiirunavaara Mine when mining production progressed beyond 700 m depth. Since 2008, significant work has been done at LKAB to better understand their induced seismicity. It has been identified that the majority of seismic events in the mine are likely caused by the interaction of mining excavations and structural geology. Two complimentary PhD projects (funded by LKAB) are underway at Luleå University of Technology to address the cause of the seismicity experienced at the mine, with one concentrating on mine seismology and one on rock mechanics.The rock mechanics project, the focus of this paper, concentrates on quantifying relationships between mining sequences, geomechanical and geological conditions, stress changes and induced seismicity at the mine. A series of numerical models will be developed based on an extensive data acquisition campaign to examine the interaction between the mining and geological systems. The role of structural geology in mine behaviour and its application to mine planning is of particular focus within these models. This paper presents the methodology of the rock mechanics project, including: data acquisition, data analysis, and numerical stress analysis models and modelling techniques

Place, publisher, year, edition, pages
Leiden: CRC Press, 2014
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-28317 (URN)2152ff8d-c664-4fc7-a178-1d801506c3d5 (Local ID)9781138001497 (ISBN)2152ff8d-c664-4fc7-a178-1d801506c3d5 (Archive number)2152ff8d-c664-4fc7-a178-1d801506c3d5 (OAI)
Conference
ISRM International Symposium EUROCK : 26/05/2014 - 28/05/2014
Note
Godkänd; 2014; 20140611 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
2. Mine-scale numerical modelling, seismicity and stresses at Kiirunavaara Mine, Sweden
Open this publication in new window or tab >>Mine-scale numerical modelling, seismicity and stresses at Kiirunavaara Mine, Sweden
2014 (English)In: Deep mining 2014: proceedings of the seventh international conference on deep and high stress mining :16-18 september 2014, Sudbury, Ontario, Canada / [ed] Marty Hudyma; Yves Potvin, Nedlands, WA: Australian Centre for Geomechanics, 2014, p. 363-376Conference paper, Published paper (Refereed)
Abstract [en]

LKAB’s Kiirunavaara Mine, located in northern Sweden, has exhibited seismic behaviour since the mining production extended below 700 m depth. Iron ore is mined from the 4.5 km long orebody via sublevel caving at a production rate of 28 million tonnes per annum. The deepest current production level is at approximately 800 m depth, and current mining plans call for mining to about 1200 m depth. It is thus of critical importance for LKAB to gain a deeper understanding of the stress and rock mass behaviour at the mine.The Kiirunavaara orebody has complex geometry and geology, which is represented using the discontinuum distinct element code 3DEC. As part of a larger series of models investigating the influence of strength and structural geology on rock mass behaviour, the results of multiple continuum models are presented. The goals of these continuum models included: i) obtain a better understanding of the virgin stress field and redistribution of stresses caused by mining, ii) further define the extent of mining induced plastic failure, and iii) increase the understanding of existing failure mechanisms at the mine.The elastic and plastic continuum models accurately produced principal stresses similar to measurements recently conducted at two sites in the mine, confirming the previously estimated virgin stress state. Spatial correlations between plastic failure in the model and seismicity in the hangingwall and footwall were found. However, these correlations were not consistent throughout either material for any evaluated set of material properties; either the plastic failure in the footwall or hangingwall corresponded well with seismicity. This may be because a set of rock mass properties which represent rock mass failure at this scale have not been evaluated or that some underlying failure mechanisms causing seismicity are not represented in the models, for example, failure along discontinuities. Some events larger than moment magnitude of 1.2 in the hangingwall, in particular shear source mechanisms events, do not correspond well with plastic failure from the model. These results potentially indicate that geological structures, which are not represented in these models, influence mine behaviour.The improved understanding of input data, rock mass behaviour, and failure mechanisms as a result of these models has a direct impact upon mine excavation design and future rock behaviour investigations, and will be used in the continued research, as well as in mine planning.

Place, publisher, year, edition, pages
Nedlands, WA: Australian Centre for Geomechanics, 2014
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-37263 (URN)b3cb328a-bb40-4dd9-9dc6-0990aefd0973 (Local ID)9780987093790 (ISBN)b3cb328a-bb40-4dd9-9dc6-0990aefd0973 (Archive number)b3cb328a-bb40-4dd9-9dc6-0990aefd0973 (OAI)
Conference
International Conference on Deep and High Stress Mining : 16/09/2014 - 18/09/2014
Note
Godkänd; 2014; 20150612 (jesvat)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
3. Developing 3-D mine-scale geomechanical models in complex geological environments, as applied to the Kiirunavaara Mine
Open this publication in new window or tab >>Developing 3-D mine-scale geomechanical models in complex geological environments, as applied to the Kiirunavaara Mine
2016 (English)In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 203, p. 140-150Article in journal (Refereed) Published
Abstract [en]

An understanding of the relationship between the geological environment and rock mass behaviour induced by mining activities can lead to hazard reduction through knowledge-based design. However, characterisation of complex and heterogeneous rock masses that typify mining environments is difficult. A methodology to characterise these types of rock masses, based largely on classical statistics, geostatistics and an extension of previous quantitative structural domaining work, is presented and applied to the Kiirunavaara Mine, Sweden. In addition to a new perspective on intact rock strengths of geological units at the mine, a correlation was found between modelled volumes of clay, modelled RQD, newly identified structural domains and falls of ground. These relationships enabled development of a conceptual model of the role of geology in rock mass behaviour at the mine. The results demonstrate that the proposed methodology can be useful in characterisation of complex rock masses.

National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-15752 (URN)10.1016/j.enggeo.2015.07.020 (DOI)000372688600013 ()2-s2.0-84959078881 (Scopus ID)f4c80667-0515-4110-b909-6cdbc900ee6a (Local ID)f4c80667-0515-4110-b909-6cdbc900ee6a (Archive number)f4c80667-0515-4110-b909-6cdbc900ee6a (OAI)
Note
Validerad; 2016; Nivå 2; Bibliografisk uppgift: Special Issue on Probabilistic and Soft Computing Methods for Engineering Geology; 20150806 (jesvat)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
4. Geomechcanical characteristics inferred from mine-scale rock mass behaviour
Open this publication in new window or tab >>Geomechcanical characteristics inferred from mine-scale rock mass behaviour
2017 (English)In: Deep Mining 2017: Eighth International Conference on Deep and High Stress Mining / [ed] J Wesselo, Perth, Australia: Australian Centre for Geomechanics, 2017, p. 555-568Conference paper, Published paper (Refereed)
Abstract [en]

As with many other mining environments, the frequency of ground falls at Luossavaara-Kiirunavaara AB’s Kiirunavaara Mine has increased with the progression of mining depth. These instabilities, which are unevenly distributed throughout the rock mass, have failure modes primarily including spalling, strainbursting, structurally controlled failure, and combinations thereof. Although caused in part by the mine-wide stress redistribution and geomechanical features of the rock mass, the exact manner in which these factors control the spatial distribution and characteristics of the ground falls not well understood. The objective of this paper is to describe the development of a geomechanical basis for how and why the distribution and characteristics of the ground falls differ throughout the rock mass. Spatial and temporal characteristics of ground falls at the mine-scale were analysed using two main forms of data: 1) a database of ground fall events, and 2) laser imaging data. A methodology was developed specifically for the use of three-dimensional laser imaging data for mine-scale analysis of overbreak and falls of ground. In conjunction with geomechanical characterisation of the rock mass, these results can be used to assist with: identification of areas with higher risk of instabilities, production planning from an induced stress management perspective, location-based support system design in advance of drifting, evaluating the performance of drift development practice in different geomechanical conditions, and data collection and usage recommendations.

Place, publisher, year, edition, pages
Perth, Australia: Australian Centre for Geomechanics, 2017
Keywords
rockfalls, overbreak, geomechanical environment, laser imaging data, data collection
National Category
Other Engineering and Technologies Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-65277 (URN)978-0-9924810-6-3 (ISBN)
Conference
8th International Conference on Deep and High Stress Mining (Deep Mining 2017), Perth, Australia, 28-30 March 2017
Available from: 2017-08-23 Created: 2017-08-23 Last updated: 2017-11-24Bibliographically approved
5. A methodology to evaluate if geomechanical features are relevant to seismic behaviour
Open this publication in new window or tab >>A methodology to evaluate if geomechanical features are relevant to seismic behaviour
(English)In: Article in journal (Refereed) Submitted
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:ltu:diva-65567 (URN)
Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2018-05-22
6. Rock mass characteristics and tomographic data
Open this publication in new window or tab >>Rock mass characteristics and tomographic data
2018 (English)In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 51, no 5, p. 1615-1619Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Springer, 2018
National Category
Other Civil Engineering
Research subject
Mining and Rock Engineering
Identifiers
urn:nbn:se:ltu:diva-65571 (URN)10.1007/s00603-018-1428-y (DOI)000431174000018 ()2-s2.0-85045062761 (Scopus ID)
Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2018-08-09Bibliographically approved

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