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Luleå, Sweden

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. Source

Vatcher J.,Lulea University of Technology | McKinnon S.D.,Queens 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. Source

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. Source

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. Source

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. Source

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