Itasca Consultants AB

Luleå, Sweden

Itasca Consultants AB

Luleå, Sweden

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Edelbro C.,Lulea University of Technology | Sjoberg J.,Itasca Consultants AB | Malmgren L.,Luossavaara Kiirunavaara AB LKAB | Dahner-Lindqvist C.,Luossavaara Kiirunavaara AB LKAB
Canadian Geotechnical Journal | Year: 2012

A likely result of changes in rock stresses due to progressing mining is an increased number of compressive stress-induced failures. This paper presents the results from numerical analysis and observations of stress-induced fallouts in footwall drifts in the Kiirunavaara underground mine. A brittle-plastic "cohesion-softening friction-hardening" (CSFH) material model was used for simulating brittle fallouts. To account for mining-induced stress changes, the local model stress boundary conditions were extracted from a global model. The rock mass properties were based on field observations in the footwall drifts as well as on results from laboratory testing. A multi-stage analysis was carried out to gradually change the stresses to simulate mining progress. A parametric study was conducted in which strength properties, location, and shape of the footwall drift were varied. Yielded elements and maximum shear strain were used as damage and fallout indicators. The modelling results were sensitive to the shape of the drift. The location of the predicted fallouts was in good agreement with the location of observed fallouts for the case in which the drift roof was simulated flatter than the theoretical cross section. The results indicate that the true shape of the drift is different from the planned one.


Umar S.B.,Lulea University of Technology | Sjoberg J.,Itasca Consultants AB | Nordlund E.,Lulea University of Technology
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

The LKAB Malmberget Mine is mined using sublevel caving. This mining method is cost-effective but results in successive caving of the host rock and mining-induced ground deformations. Consequently, re-locations of residential areas have been in progress in Malmberget ever since iron ore extraction on industrial scale commenced about a century ago. This study seeks to increase the understanding of the intrinsic characteristics of the rock mass governing deformation and caving activities. Rock mass characterizations were done in two selected orebodies - Printzsköld and Fabian. Two drill holes were drilled in each orebody from the surface. Geotechnical core logging was performed using the RMR system. Weakness zones were categorized to determine what role they played in the caving process. Point load testing was conducted for a sampling interval of about 5 m and selected uniaxial compressive strength tests were conducted to calibrate the point load index. Tunnel mapping was conducted in the hangingwall of the Printzsköld orebody. The finite element modeling code Phase2 was used for a sensitivity analysis of rock strength parameters and to study factors that may influence initiation of caving of the hangingwall. Copyright 2013 ARMA, American Rock Mechanics Association.


Vatcher J.,Lulea University of Technology | McKinnon S.D.,Queen's University | Sjoberg J.,Itasca Consultants AB
Engineering Geology | Year: 2015

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. © 2015.


Juncal A.S.,Itasca Consultants AB | Ivars D.M.,Itasca Consultants AB | Brzovic A.,Codelco Division El Teniente | Vallejos J.,University of Chile
Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium | Year: 2014

Application of hydraulic fracturing for preconditioning of hard rock in underground caving mines has been demonstrated to be an effective means to induce and promote cave growth. Using Itasca's particle flow code PFC 2D, a real scale numerical test environment has been developed to assess the effect of preconditioning by hydraulic fracturing on primary fragmentation. The environment makes use of the synthetic rock mass (SRM) method to simulate the mechanical behavior of hard rock mass. This technique uses the bonded particle model for rock to represent intact material and the smooth-joint contact model (SJM) to represent the in situ discontinuities and the induced hydraulic fractures. A series of hypothetic scenarios of veined hard rock mass (stockwork) based on El Teniente mine has been simulated using this environment. The results emphasize the impact of preconditioning on primary fragmentation in veined hard rocks. © 2014 Taylor & Francis Group, London.


Vallejos J.A.,University of Chile | Suzuki K.,University of Chile | Brzovic A.,Codelco Division El Teniente | Ivars D.M.,Itasca Consultants AB
International Journal of Rock Mechanics and Mining Sciences | Year: 2016

Rock masses of the primary copper ore at the El Teniente mine fail mainly through the infill of preexisting veins during the caving processes, especially through those composed of less than 35% hard minerals (quartz and pyrite). In this study, the Synthetic Rock Mass (SRM) approach is used to reproduce the results of ten uniaxial compression tests on veined core-size samples of El Teniente Mafic Complex (CMET) lithology, from El Teniente mine, Codelco-Chile. At the scale of the tested samples it is observed that veins composed mostly of quartz dominate the failure process. The developed methodology considers generating a deterministic Discrete Fracture Network (DFN) based on the veins mapped at the surface of each core sample. Then, the micro-parameters of the Bonded Particle Model (BPM) are calibrated to represent the macro-parameters of the average block of intact rock within all samples. Next, the micro-parameters of the Smooth-Joint Contact Model (SJCM), which represent the mechanical properties of veins, are calibrated to reproduce the stress-strain curves and the failure modes of the veined core-size samples measured during the laboratory tests. Results show that the SRM approach is able to reproduce the behavior of the veined rock samples under uniaxial loading conditions. The strength and stiffness of veins, as well as the vein network, have an important impact on the deformability and global strength of the synthetic samples. Contrary to what was observed in the laboratory tests, synthetic samples failed mainly through weak veins. This result is expected in the modeling given that anhydrite veins are considered weaker than quartz veins. Further research is required to completely understand the impact of veins on the behavior of rock masses. © 2015 Elsevier Ltd.


Alejano L.R.,University of Vigo | Veiga M.,Itasca Consultants AB | Taboada J.,University of Vigo | Diez-Farto M.,S. A. de Obras y Servicios COPASA
Geotechnique | Year: 2012

A limit-equilibrium-based technique is proposed for the design and analysis of drystone masonry retaining walls, focusing particularly on granite walls as traditionally constructed in Galicia in northwest Spain. To date, walls have typically been designed on the basis of past experience and rigid wall approaches. The method presented analyses wall stability, at different heights associated with block rows, against sliding and against two overturning mechanisms. As a result, design widths are obtained for different wall depths. The method can also be applied to estimates of the stability of existing walls with known dimensions and properties. The analytical method was applied experimentally to the design of a 20 m high wall. A sensitivity analysis of the design was also performed, with results presented in the form of a spider diagram. Estimates of the most relevant parameters for this type of design and some back-analyses to assess the technique are addressed in an accompanying paper.


Sjoberg J.,Itasca Consultants AB | Savilahti T.,LKAB
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

The Fabian orebody is a non-daylighting iron orebody in the LKAB Malmberget Mine in northern Sweden. The orebody was mined using slot caving and sublevel stoping during the 1970s and 1980s, resulting in a large open stope under a 250 m thick crown pillar. The orebody has since been mined using sublevel caving beneath the open stope, which has caused progressive caving and a corresponding continuous reduction of the crown pillar thickness toward the ground surface. During 2010, a prognosis of the cave development in the Fabian area was developed, based on compilation and analysis of all available material. At this time, the crown pillar had a minimum thickness of 77 m. The prognosis was presented at the end of 2010, and predicted a slow, progressive caving of the crown pillar and the formation of a cave crater on the ground surface within the previously fenced-off area, and with minor disturbance to the surrounding municipality. The cave development was followed up continuously through laser scanning, visual observations and seismic monitoring. In March 2012, a new cave crater formed on the ground surface above the Fabian orebody, similar to what was predicted. The crater developed in the morning of March 20, with no disturbances to nearby residents or municipal functions. The prognosis is compared with observations of the caving and the differences and implications quantified. A program for continued monitoring of mining-induced deformation in Malmberget is also described and a criterion for allowable mining-induced surface deformations is proposed. © 2014 by Japanese Committee for Rock Mechanics.


Sjoberg J.,Itasca Consultants AB | Perman F.,Itasca Consultants AB | Quinteiro C.,LKAB | Malmgren L.,LKAB | And 2 more authors.
Transactions of the Institutions of Mining and Metallurgy, Section A: Mining Technology | Year: 2012

Mining in the production area Block 19 in the LKAB Kiirunavaara Mine has resulted in extensive seismic activity and several serious rockfalls. This paper describes a modelling study aimed at quantifying the seismic potential for future mining of Block 19, considering several different mining sequences. A three-dimensional discontinuum model was used, in which geological structures were included explicitly to simulate the development of fault slip seismic events. Four different mining sequences were simulated: three of which involved leaving the whole, or part of, Block 19 as an unmined pillar. Mining was simulated from the current active mining level and for a production period of ≥20 years ahead in time. The results were evaluated in terms of stress influences on critical infrastructure in the footwall of Block 19 and, more importantly, the possible extent of fault slip seismic events due to mining (by calculating seismic moments). The results showed that leaving a pillar in Block 19 may be less desirable as higher seismic moments will develop in the final mining stages. However, continued mining without a pillar will also likely result in an increased seismic activity in Block 19, which needs to be addressed appropriately. Block 19 should be mined before the neighbouring production areas, but additional and more detailed numerical modelling may be needed to fine-tune the extraction sequence for each level mined. © 2012 Australian Centre for Geomechanics, The University of Western Australia.


Alejano L.R.,University of Vigo | Veiga M.,Itasca Consultants AB | Gomez-Marquez I.,University of Vigo | Taboada J.,University of Vigo
Geotechnique | Year: 2012

This paper applies the analytical limit-equilibrium technique described in the accompanying Part I of this article to the design of granite drystone masonry retaining walls. Particular attention has been paid to estimating relevant parameters for the materials used. The friction angle between the stone blocks was studied by means of fullscale tests, and an empirical method was used to estimate the backfill strength properties. The dip of the base of the part of the wall tending to overturn was also studied. The technique was tested by back-analysing three wall failures, and was compared with numerical results from the UDEC code, suggested as an appropriate approach for assessing analytical results. Analytical factor of safety results for the design of a 20 m-high wall compared well with the numerical approach used in combination with the shear strength reduction technique. The results confirm the suitability of the limit-equilibrium approach for analysing these traditional, cost-effective and environmentally friendly structures.


Alejano L.R.,University of Vigo | Rodriguez-Dono A.,University of Vigo | Veiga M.,Itasca Consultants AB | Veiga M.,University of Vigo
Tunnelling and Underground Space Technology | Year: 2012

We describe techniques to estimate plastic radii and longitudinal deformation profiles of tunnels excavated in rock masses. The longitudinal deformation profile, a graph that relates a fictitious internal pressure to the distance to the tunnel face, is necessary to assess adequate distance to the face for the purpose of installing support. Traditional application of this method usually relies on an elastic representation of the longitudinal deformation profile. A more realistic approach has been proposed recently that accounts for the elastoplastic nature of rock masses. It is based, however, on assuming elastic-perfectly plastic rock mass behaviour, an assumption which is more or less realistic, but only for low quality rock masses with a geological strength index (GSI) below 35. We extend this approach to the case of strain-softening rock masses representing a wider range of rock masses (25. <. GSI. <. 75). Based on studying various numerical techniques to estimate these curves, we propose a simplified approximate equation of the plastic radius of a tunnel excavated in a strain-softening rock mass, which can be combined with existing longitudinal deformation profile estimation techniques to analytically obtain a more realistic approach to calculating longitudinal deformation profiles for strain-softening rock masses. © 2012 Elsevier Ltd.

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