Stability and design of stope roofs and sill pillars in cut-and-fill and open stope mining with application to the Zinkgruvan Mine

Godkänd; 1992; 20080404 (ysko)</p

Analysis of large scale rock slopes

The objective of this work was to (1) increase the knowledge of the behavior of large scale rock slopes, (2) improve the ability to estimate rock mass strength for such slopes, and (3) develop an improved design methodology for forward design of large scale slopes in open pit mining. A fourth objective included the application of the results to the Aitik open pit in northern Sweden. A large number of case studies were collected into a database and empirical design guidelines were developed. A procedure for determining the strength of large scale slopes was developed, based on the Hoek-Brown failure criterion. Failure mechanisms of high slopes were studied using numerical modeling. The procedure for strength estimation and the modeling methodology, were applied to selected case studies-this enabled verification of the design methodology. Finally, the design methodology was applied to the Aitik open pit mine, and slope design recommendations given.Godkänd; 1999; 20061117 (haneit

Large scale slope stability in open pit mining : a review

Design of open pit slope angles is becoming more and more important as the mining depths of open pits continuously increase. Small changes in the overall pit slope angle have large consequences on the overall economy of the mining operation. A case in particular is the Aitik open pit mine in northern Sweden, which currently faces the design of the overall slope angles for continued mining toward a depth of around 500 meters. This report constitutes the first phase in a research project aimed at developing design methods for large scale pit slopes. In this report, the stability and design of large scale pit slopes in open pit mining is reviewed, with special reference to slopes in hard, jointed, rocks, similar to the rock types found at the Aitik mine. The review covers the mechanics of pit slopes, existing design methods for large scale slopes, remedial measures and mining strategy to cope with slope failures, and a compilation of case studies from open pits worldwide. Finally, suggestions for future research in this area are presented. The factors governing large scale slope stability are primarily: (1) the stress conditions in the pit slopes, including the effects of groundwater, (2) the geological structure, in particular the presence of large scale features, (3) the pit geometry, and (4) the rock mass strength. Observed failure modes in rock slopes are of a wide variety. On a bench scale, structurally controlled failures such as plane shear and wedge failures are common. However, as the scale increases, simple structurally controlled failures are less dominate, and more complex failures such as step-path failures start to develop. From observations, it appears that for large scale slopes, two failure modes are especially important to consider. These are (1) rotational shear failure, and (2) large scale toppling failure. Rotational shear failure in a large scale slope involves failure both along pre-existing discontinuities and through intact rock bridges, but where the overall failure surface follows a curved path. Large scale (or deep seated) toppling failures have been observed in several large scale natural slopes and high open pit slopes. The mechanisms behind large scale failures are, however, not well known, in particular for hard, strong rocks. Criteria for the shape and location of the failure surface are lacking, as is detailed knowledge regarding failure through intact rock versus failure along discontinuities. Knowledge of the kinetic behavior of failing rock slopes is mostly empirical and requires more studies, in particular for hard and brittle rock masses in which rapid failures can be expected. This review has shown that the strength of a large scale rock mass is very difficult to assess. At the same time, the required accuracy for the strength parameters which are needed for the design is very high. For large scale rock masses, back-analysis of previous failures proves to be the only practical means of obtaining relevant strength parameters. However, the interpretation and translation of such data from one geological environment to another, is very cumbersome and lined with problems. Design methods for rock slopes can divided into mainly four categories, namely: (1) limit equilibrium methods, (2) numerical modeling, (3) empirical methods, and (4) probabilistic methods. The advantages and disadvantages of each of these methods are discussed in the review. For the design of large scale slopes, it appears that the choice of design method is less important than the choice of input parameters to the design, in particular the rock mass strength parameters. Remedial measures for controlling the stability of slope include support and drainage. While support can work for small scale slopes, only drainage is feasible for increasing the stability of large scale slopes. Monitoring of displacements, preferably using survey networks, should be carried out routinely in all open pit mining. Provided that the failure is slow and stable, it is also possible to continue to mine a failing slope. This requires that contingency plans are being made at an early stage in the mine planning process. From the collection of a number of case studies from North and South America, Africa, Asia and Europe, several examples of large scale failures were found, although mostly occurring in weak rocks. There are much fewer examples of slope failures in hard, brittle rocks. The few cases found indicate that failures in this type of rock is more uncontrollable. A compilation of slope height, slope angles, rock strength, and stability conditions for the studied cases concludes this chapter. Future research in the field of large scale slope design must be focused on quantifying the mechanisms for large scale slope failures. Once the mechanisms are better known, design methods based on the actual slope mechanics can be employed. Also, better and more reliable methods for determining the strength of large scale rock masses are important to develop.Godkänd; 1996; 20080527 (ysko

Sjuksköterskors upplevelse av moralisk stress : En deskriptiv litteraturstudie

Bakgrund: Stress är vanligt förekommande hos yrkesverksamma sjuksköterskor och nämns som en grundläggande orsak till psykisk ohälsa och ökat antal sjukskrivningar. Arbetsmiljöverket rapporterar in yrkesrelaterad stress som den vanligaste sjukskrivningsorsaken bland vårdpersonal. Moralisk stress definieras som situationer då vi vet vad som är rätt att göra, men institutionella begränsningar gör det i princip omöjligt att göra det rätta. Syfte: Att beskriva sjuksköterskors upplevelser av moralisk stress. Metod: En deskriptiv litteraturstudie med tematisk dataanalysmetod som utgår från 13 vetenskapliga artiklar som svarar på studiens syfte.  Huvudresultat: Resultatet visade att när det finns brister i behandlingen som patienterna erhåller och kvaliteten på vården sviktar upplever många sjuksköterskor moralisk stress. Det visade även att samarbetssituationer, kommunikationsbrister och kontakter med anhöriga kan vara källor till moralisk stress. Den moraliska stressen utlöstes i de situationer där sjuksköterskor upplever att patienterna blir lidande och då sjuksköterskan upplever att hon inte kan agera på det sätt som är bäst för patienten. Som en konsekvens av den moraliska stressen upplever sjuksköterskorna flera varierande negativa känslor, där frustration är den mest frekventa känslan. Slutsats: Upplevelser av moralisk stress är vanligt förekommande bland kliniskt arbetande sjuksköterskor. Den moraliska stressen uppkommer i situationer där sjuksköterskor inte kan agera på det sätt som sjuksköterskorna anser är rätt. Som en konsekvens av den moraliska stressen upplever sjuksköterskorna flera olika negativa känslor. Genom att få en förståelse för vad moralisk stress är, hur den uppkommer och hur den yttrar sig känslomässigt kan sjuksköterskor lättare hantera sina egna reaktioner då de upplever moralisk stress.Background: Stress is common among nurses and is mentioned as a fundamental cause of an increased number of sick leaves and mental illness. The Swedish Work Environment Authority reports occupational stress as the most common cause of sick leave among healthcare professionals. Moral distress is defined as situations when we know what is right to do, but when institutional limitations make it impossible to do the right thing. Aim: The aim of this study was to describe nurses' experience of moral distress.  Methods: A descriptive literature study with a thematic data analysis method based on 13 scientific articles that answer the aim. Main results: The result revealed that deficiencies in the treatment that patients receive and the quality of care declines, many nurses experience moral distress. It also revealed that cooperation situations, deficiencies in communication and contacts with relatives can be sources of moral distress. The moral distress is triggered in the situations where nurses feel that the patients are suffering and when the nurse feels that she cannot act in the best way for the patient. As a consequence of the moral distress, the nurses experience several varying negative emotions, where frustration is the most frequent emotions. Conclusion: Experiences of moral distress are common among clinically working nurses. The moral distress arises in situations where nurses can’t act in a way that the nurses think is right. As a consequence of the moral distress, the nurses experience several different negative emotions. By gaining an understanding of what moral distress is, how it arises and how it manifests emotionally, nurses can more easily manage their own reactions when they experience moral distress

Rock mass characteristics and tomographic data

Full text license: CC BY</p

Geomechcanical characteristics inferred from mine-scale rock mass behaviour

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.ISBN för värdpublikation: 978-0-9924810-6-3</p

Mine-scale numerical modelling, seismicity and stresses at Kiirunavaara Mine, Sweden

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.Godkänd; 2014; 20150612 (jesvat

Modelling of caving and deformation mechanisms of the hangingwall of the Printzsköld oreboby at Malmberget mine

Sublevel caving in Malmberget mine results in mining-induced surfacedeformation. One of the currently mined orebodies is the Printzsköldorebody. As mining deepens there is need to assess the behaviour of thecave formed in the subsurface above this orebody. Numerical analysis wasused to assess the effects of extraction to deeper levels and performstrength parametric studies. Stress redistribution was studied, and theresults showed high stress buildups in the hangingwall and the crownpillar. Two failure mechanisms have been identified – shear and tensile.Reducing cohesion by 50% increased the area of the yielded zone by morethan 100% in the hangingwall.Validerad;2017;Nivå 2;2017-06-13 (andbra)</p

Mine-scale numerical modelling, seismicity and stresses at Kiirunavaara Mine, Sweden

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.Godkänd; 2014; 20150612 (jesvat

Rock mass characterization and conceptual modeling of the Printzsköld orebody of the Malmberget mine, Sweden

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 tostudy factors that may influence initiation of caving of the hangingwall.Validerad; 2013; 20131129 (sraban)</p