| 61. |
- Clarin, Mattias
(författare)
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Plate buckling resistance : patch loading of longitudinally stiffened webs and local buckling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Incremental launching of steel bridges is a demanding undertaking, on the erection site as well as on the designers desk. Not seldom, the structure itself is during the launching subjected to high concentrated forces on the lower flange when passing over the launching shoe or a intermediate support (e.g. column). These concentrated forces, commonly referred to as patch loads, may be of such magnitude that it governs the thickness of the web in the bridge girder and a small increase in web thickness leads to a substantial gain of steel weight of the bridge. Hence also a higher material cost. One solution to this problem is to reduce the buckling length of the web with the use of a longitudinal stiffener of open (a plate) or closed type (closed profile of e.g. V-shape). The improved patch load resistance is in the Eurocode nowadays determined with the help of the yield resistance for the web and contributing parts of the loaded flange reduced with a factor dependent of the slenderness of the web and the influence of the longitudinal stiffener. Parts in the expressions for the yield resistance and the reduction factor have been somewhat questioned and over the years a substantial amount of tests and FE simulations of longitudinally stiffened webs has been carried out. This research work has produced a large amount of test data which has been used herein to further improve the prediction of the patch load resistance of longitudinally stiffened steel girder webs. Based on the use of the gathered test data from the literature and previously done research, a calibrated patch load resistance function was developed for both open and closed longitudinal stiffeners. Furthermore, a partial safety factor for the proposal was determined according to the guidelines in the Eurocode. In all, the proposal was proven to have an improved level of prediction than other comparable proposals (e.g. Eurocode). Another questioned part in the commonly used design codes is the reduction function concerning local buckling under uniformly in-plane compression. The nowadays used function (the Winter function) has been developed during the 30-ies based on tests on cold formed specimens and has been criticized as being too optimistic regarding plates with large welds. At LTU a series of tests on welded specimens made of high strength steel with large welds was conducted to investigate the aforementioned concerns. Along with test data found in a literature survey, the tests showed that the Winter function was shown to be too optimistic and a new reduction function, based on the test data, was proposed also for this application.
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| 62. |
- Cupillard, Samuel
(författare)
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Thermohydrodynamics of sliding contacts with textured surfaces
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrodynamic sliding contacts like those found in journal or thrust bearings are frequently encountered in various types of machinery from computers to large turbines. These contacts, involving a variation in film thickness, are used to generate pressure in the lubricant film and separate the surfaces in relative motion. The contacts must carry a load while maintaining friction as low as possible. Environmental and economic concerns require the machines to operate with minimal power consumption. A number of design modifications have been proposed over the years in order to improve performance of such hydrodynamic contacts. There are experimental indications that textured surfaces, composed of a pattern of well-defined identical shapes, can improve hydrodynamic performance. There is therefore a need to understand and explain the effects of textured surfaces on hydrodynamic contact performance. A Computational Fluid Dynamics (CFD) analysis of the flow field can provide such an understanding. The full Navier-Stokes equations are solved using CFD code for both a slider and a journal bearing. Thermal and cavitation effects are considered. Numerical techniques that deform the computational grid in time are used to recalculate the film gap and simulate the motion of a microgroove located on a moving surface.For a texture located in the inlet part of the stationary surface of an inclined slider, the pressure build-up mechanism is investigated. Such a texture decreases losses locally and allows for increased pressure and a higher load carrying capacity. A critical value of the texture depth separates positive and negative effects of inertia on the load carrying capacity of the slider. The texture studied here provides maximum efficiency when its depth is such that the lubricant flow occurs at the onset of recirculation. In 3D, the texture length should be close to the pad length to generate the highest load carrying capacity. Improvements in performance are shown for different operating conditions. One important effect is that the load carrying capacity of the slider can be increased by up to 16% under severe thermal operating conditions. A journal bearing textured with microgrooves on the stationary surface is investigated. The coefficient of friction can be reduced if grooves of suitable depth are introduced. Under light loading (eccentricity ratios less than 0.15), shallow microgrooves (with a depth less than the minimum film thickness) placed in the maximum film region increase the minimum film thickness while reducing the friction force. The load carrying capacity is enhanced based on the same principle as for the inlet textured slider. Under high loading (eccentricity ratios greater than 0.5), deep microgrooves (with a depth greater than the minimum film thickness) placed in the maximum pressure region reduce both friction force and minimum film thickness. Nevertheless, for high loading, the texture provides better reduction in friction force than a smooth bearing operating with a thinner lubricant.A microgroove positioned on the moving surface, i.e., on the shaft of a journal bearing is also studied. A 2D isothermal case is investigated to explain the effect of the microgroove on the pressure profile and the behaviour of the load carrying capacity over one shaft revolution. The microgroove decreases pressure locally at every circumferential position, resulting in a decrease in the averaged load carrying capacity. A 3D thermal case is analysed to show how lubricant transport is modified by a microgroove. The microgroove affects thermal mixing as it carries a greater amount of cold lubricant to regions with high temperatures. This effect, more pronounced with deeper microgrooves, is due to a global flow recirculation inside the microgroove, which improves mixing.
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| 63. |
- Dahlén, Lisa
(författare)
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Household waste collection : factors and variations
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ambitious household waste recycling programs have been introduced in Sweden and several other countries during recent decades. Many different waste- sorting and collection schemes have been developed, but the evaluation and comparison of the results is made difficult by the lack of comparable data. The aim of the research presented in this thesis was to answer the following questions: How can household waste flows be described and monitored? Which factors affect the collection results? and, What is a useful basis for the evaluation of collection systems? Waste flow analysis and waste component classification were performed in a number of Swedish municipalities, revealing a wide variation in the amount of waste per capita. Eleven site-specific variables were investigated and multivariate data analysis was performed. The study was carried out on three levels: 1) household waste as the material in itself, classified into physical components, 2) the householders and their handling of waste, in terms of average amounts of different waste categories and recyclables per capita, and 3) the municipalities, as the authority responsible for household waste management, where local conditions influence waste generation and pathways. A significant finding was that property-close collection of dry recyclables led to increased collection of sorted metal, plastic, and paper packaging. Weight-based billing, i.e. when waste collection is charged per kilogram of waste collected, showed divergent effects, which are investigated and discussed. Monitoring methods are suggested regarding the waste flow from households. A step-by-step method for evaluation and comparisons of collection systems was outlined, including a set of indicators. Sixteen sources of error in official waste statistics were identified and the results of the studies emphasize the importance of reliable waste generation and composition data to underpin waste management policies.
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| 64. |
- Danell, Mats
(författare)
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På tal om elevinflytande : hur skolans praktik formas i pedagogers samtal
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Educational research shows that it is problematic to implement the curriculum's intentions in the practice of schools. Within this problem area I have studied how the curriculum's intentions about student influence are shaped by pedagogues. The results of my licentiate report showed that the circumstances of the work governed the way in which the pedagogues came to shape the students' influence. The present thesis presents a deeper study of this area in order to describe and understand how student influence is shaped in schools. The aim of the thesis is thus to describe and provide an understanding of how student influence is constructed in staff conversations taking place in working teams of pedagogues. In the study I have followed a team working within the framework of a renewed development strategy. The purpose of the altered strategy has been to increase the pedagogues' influence and participation in school development. In the study I have observed five staff conversations in which the pedagogues of the working team discussed the school's work with student influence. The conversations were tape-recorded and then transcribed. The texts were analysed in order to study how the student influence was shaped through staff conversations. As a point of departure for explaining the object of study I have used a theoretical frame of reference starting out from sociology of knowledge (Berger & Luckmann, 1967), social constructionism with links to Mikhail Bakhtin, Jürgen Habermas and Ludwig Wittgenstein. The methodological implementation has been inspired by ethnomethodology and critical discourse analysis. The results show that the working team did not contribute to any great extent to realising the curriculum's intentions about student influence. On the other hand, it was evident that the pedagogues used different strategies in the staff conversations. Through these strategies they guarded their control of their individual scope of action for modifying how and by what means student influence should be implemented. The strategies used appeared as three main lines with specific patterns. These lines and patterns are accounted for in the study with the aid of a number of empirical concepts. In the first main line, called conceptual shifting, there appeared patterns of conceptual neutralisation, practical loading and conceptual change. In the second main line, called attention shifting, there appeared patterns termed situation adapted management, selective attention and goal shifting. In the third main line, called problem shifting, there were patterns termed circumstantial explanations and excuses. The study thus show that through the staff conversation the pedagogues have created a "free space" in which they construct student influence by taking as their starting-point the intentions that they conceive of as possible to realise. They have developed a battery of strategies in order to be able to handle their own practice. The strategies may be understood as an effect of the pedagogues being forced to handle the paradoxes that have arisen in the field of tension between a desired and a possible school. The results indicate a need for further research in order to reach a deeper understanding of how pedagogical activities develop at the micro level, such as in all the meetings and conversations that pedagogues take part in.
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| 65. |
- Danvind, Jonas
(författare)
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Analysis of drying wood based on nondestructive measurements and numerical tools
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improved understanding of moisture and mechanical behaviour is a general objective for wood drying research. The main objective of this doctoral thesis was to develop nondestructive experimental methods suitable for collecting valuable response data related to the moisture behaviour and mechanical behaviour of drying wood and to refine this information into modelling parameters. A method for simultaneous noncontact measurement of two-dimensional surface deformations and interior densities was developed. This was done using Digital Speckle Photography (DSP) and X-ray Computed Tomography (CT). Displacements and densities were used for calculation of strain and of moisture content. Experimental tests of the measurement method were done on cross sections of Scots pine. The following accuracy was stated for different properties: A typical calculated displacement error of approximately 10 micrometre was found. Strains derived from the displacements had a maximal error of 1.11 mstrain. Moisture content measuring accuracy was estimated to +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size 2 x 2 x 1.5 mm3. A similar noncontact technique based only on X-ray CT scanning was developed. Displacements were then estimated from boundary movements of an object in CT images. The estimated standard deviation of the measured moisture content error for this method was 0.04% moisture content. The mean error was unknown. Two different approaches to determining moisture diffusion coefficients from the studied data were presented. The first was based on minimizing the difference between measured and computed values through an optimization scheme. This approach required an initial assumption of the functional form of the diffusion coefficient. The second approach calculated diffusion and mass transfer coefficients through direct finite difference calculations on measured moisture content data. Results on Norway spruce showed interesting local variations of the diffusion coefficient, especially near the evaporation surface. Comparisons between measured and FEM simulated data showed good results. An example showed that a multivariate method of analysis could be an effective and easy-to-use tool for untangling relationships between variables and for generating information from data. Finally, it could be stated that the methods presented will be of use to improve the understanding of the behaviour of drying wood, with the focus on moisture and mechanical properties.
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| 66. |
- Davidsson, Niklas
(författare)
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Stability and transition in the suction boundary layer and other shear flows
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bypass transition has been studied by theoretical and numerical procedures, with the asymptotic suction boundary layer (ASBL) in focus. As reference cases the Blasius boundary layer (BBL) and a free shear flow have been studied. In order to reduce energy losses associated with flow systems, it is a wish to avoid turbulence in these flows. It is thus necessary to have a fundamental understanding of the mechanisms behind bypass transition, which typically starts with the formation and growth of structures extended in the streamwise direction, so called streaks. One way of delaying the transition to turbulence is to apply wall suction, which is also known to stabilize streaks. In this work, it is shown that the stabilizing mechanism of wall suction is not unambiguous. A theoretical study on the linear evolution of streaks triggered by a localized disturbance is performed. Releasing the disturbance in the free-stream, it will migrate towards the wall and quickly be subject to shear. Consequently, this disturbance is amplified when applying wall suction, provided that for the suction-free case the growth of the BBL may be considered small. When initiating the disturbance inside the boundary layer, on the other hand, it is found that suction stabilizes the growth of such a streak. Also, the non-linear properties of suction are studied using a model with prescribed wall-normal disturbance velocity identical for the ASBL and the BBL. Despite the similarity, suction is shown to dampen the non-linear forcing of the perturbation. Moreover, the non-linear response is shown to favor the forcing of streamwise longitudinal (3D) structures and 2D waves. For the ASBL, also energy thresholds for transition of periodical disturbances have been determined by direct numerical simulations. The least energy required to reach transition is obtained when the initial flow field consists of two oblique waves, for which the threshold value is found to scale as Re^{-2.6}. For transition starting with streamwise vortices or random noise the threshold scales like Re^{-2.1} (Re being the Reynolds number), and the routes to transition are similar to that of other flows. A theoretical framework for evaluating the non-linear interaction terms of the normal- velocity/vorticity equations is also developed. This formulation allows for study of wave interaction throughout the whole wavenumber plane, i.e. for any given wave number of a disturbance. The framework has been applied to a free shear flow, which shows that primarily streamwise elongated structures and Tollmien-Schlichting waves are forced by the non-linear interactions. Besides that, the geometrical interpretation shows that the non-linear interaction involving normal vorticity is most potent for structures inter-angled by 90 degrees in the wavenumber plane.
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| 67. |
- Domkin, Konstantin
(författare)
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Constitutive models based on dislocation density : formulation and implementation into finite element codes
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Correct description of the material behaviour is an extra challenge in simulation of the materials processing and manufacturing processes such as metal forming. Material models must account for varying strain, strain rate and temperature, and changing microstructure. This study is devoted to the physically based models of metal plasticity - dislocation density models, their numerical implementation and parameter identification. The basic concepts of dislocation density modelling are introduced including the effects of static and dynamic recovery, influence of strain path and modelling of the back-stress. Possible mechanisms controlling athermal and thermally activated processes involving dislocations, vacancies and solute atoms are also discussed. Mobile and immobile dislocation densities, vacancy concentrations and other variables are treated as internal state variables. The dislocation models are incorporated in a classical continuum plasticity or viscoplasticity framework by means of the evolution equations for these internal variables which effectively control the hardening behaviour. Implementation of these models into finite element codes is straightforward and numerically efficient. Dislocation models are implemented in user material subroutines and used in simulations of sheet metal forming and extrusion. The models are also implemented in a custom toolbox for parameter optimisation in Matlab. A special extended version of a return-map stress update algorithm and its consistent tangent are derived to accommodate the complex coupling effects in a material model, in which all thermo-elastic and hardening properties may depend on the plastic strain. Numerical difficulties of parameter optimisation such as non-uniqueness of the solution, high sensitivity to the starting guess-value and to the choice of the error function appear to be a common problem with advanced material models. Simultaneous curve-fitting of multiple experimental curves of different mechanical testing types is advised to achieve more robust optimisation results. Parameters of dislocation density models usually have clear physical interpretation, and it is possible to obtain values of some of them from sources other than mechanical testing. The accuracy of physically based models is totally dependent on finding the adequate equations to describe the physical processes dominating the material behaviour during deformation. These equations may be more or less accurate than standard engineering models or data interpolation approaches. However, the use of physically significant parameters related to the microstructure properties such as grain size etc gives a natural way to couple them to the models for microstructure evolution, which is important in simulations of manufacturing processes.
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| 68. |
- Drugge, Mikael
(författare)
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Interaction aspects of wearable computing for human communication
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the use of wearable computers for aiding human communication over a distance, focusing on interaction aspects that need to be resolved in order to realize this goal. As wearable computers by definition are highly mobile, always on, and always accessible, the ability to communicate becomes independent of place, time and situation. This also imposes new requirements on the user interface of the wearable computer, calling for natural and unobtrusive interaction with the user.One of the key challenges in wearable computing today is to streamline the user’s interaction, so that it is tailored for the situation at hand. A user interface that takes too much effort to use, interrupts or requires more than a minimum of attention, will inevitably hamper the user’s ability to perform tasks in real life. At the same time, human communication involves both effort, interruptions and paying attention, so the key is to find a balance where wearable computers can aid human communication without being intrusive. To design user interfaces supporting this, we need to know what roles different aspects of interaction have in the field of wearable computing. In this thesis, the use of wearable computing for aiding human communication is explored around three aspects of interaction.The first aspect deals with how information can be conveyed by the wearable computer user, allowing a user to retrieve advice and guidance from experts, and remote persons to share experiences over a distance. The thesis presents findings of using wearable computing for sharing knowledge and experience, both for informal exchange among work colleagues, as well as enabling more efficient communication among health-care personnel. The second aspect is based on findings from these trials and concerns how the wearable computer interacts with the user. As the user performs tasks in the real world, it is important to determine how different methods of notifying the user affects her attention and performance, in order to design interfaces that are efficient yet pleasant to use. The thesis presents user studies examining the impact of different methods of interruption, and provides guidelines for how to make notifications less intrusive. The third and final aspect considers how the user’s physical interaction with the wearable computer can be improved. The thesis presents rapid prototyping of systems employing user centric design. Furthermore, a framework for ubiquitousmultimedia communication is presented, enabling wearable computers to be dynamically configurable and utilize resources in the environment to supplement the user’s equipment.All in all, the thesis presents how wearable communications systems can be developed and deployed, how their human-computer interaction should be designed for unobtrusive operation, and how they can come to practical use in real world situations.
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| 69. |
- Dwari, Ranjan
(författare)
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High ash non-coking coal preparation by tribo-electrostatic dry process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coal is the single largest fossil fuel used world-wide and accounts for more than 60% of the total commercial energy consumed. Between 60 to 80% of this coal is used for electric power generation and most of which through a system of pulverised coal combustion. Major portion of the coal used for such power generation is not clean enough to maintain environmental standards. This problem is attributed to high sulphur content in coal used in most of the western countries or ash as is the case in countries like India. In India at present nearly 260 million tonnes per year of coal is used for power generation and the average ash in coals used is invariably above 40%. A substantial portion of ash is liberated as it enters the boiler from the mill. It is crucial to reduce the amount of ash going from the mill to the boilers not only to improve the performance of power generation and increase the life of the boilers but also became mandatory due to environmental regulations. Thus the main objective of the work is to develop a dry tribo-electrostatic process for the separation of ash forming inorganic matter from coal material with a thorough understanding of the response and behaviour of coal and non-coal matters to contact electrification and in electric field. This work is financially supported by the Department for Research Cooperation of the Swedish International Development Cooperation Agency (SIDA/SAREC). The literature on dry coal preparation processes has been reviewed and the advantages of triboelectric process compared to other processes have been highlighted and further research needs to make it a viable industrial technology are outlined. Three Indian coal samples from three different major coal fields, i.e., Ramagundam, Ib-valley and Talcher, have been collected and characterised for macerals and mineral composition by microscopic and XRD analyses. The beneficiation potential at different size fractions of the coal samples is judged by the washability studies. The charge polarity and magnitude of pure quartz, pyrite kaolinite, illite and carbon after contact electrification with different tribo-charging media have been measured by Faraday cup method using Keithley electrometer. The predicted work functions of the tribo charging material and mineral phases agree closely with the reported values. The electron accepting and donating (acid-base) property of mineral phases determined by Kr¨¹ss Tensiometer through polar and non-polar liquid contact angles on solids also corroborated the acquired charge polarity in contact electrification with copper, aluminium and brass materials underlying their work functions. This methodology can be applied for the choice of organic acidic/basic solvents treatment of coal material to enlarge the difference in work functions between the tribo-charger and mineral phases, and to achieve greater separation efficiency of inorganic matter from coal. The process of tribo-electric coal/ash cleaning is carried out with a newly built cylindrical fluidised-bed tribo-charger with internal baffles, made up of copper metal, and the influence of equipment and process variables have been evaluated. The collecting bins of the material underneath the copper plate electrodes are designed to function as Faraday cups such that the charge polarity and magnitude of particles in each bin can be measured directly. The coal and mineral particles respectively charged with positive and negative polarities with relatively higher magnitude illustrating greater efficiency of contact electrification in the fluidised bed tribo- charger system. The separation results with minus 300 ¦Ìm size fraction of coal containing 43% ash showed that the ash content can be reduced to 18% and 33% with an yield of about 30% and 67% respectively. With a 30% ash coal, a clean coal of about 15% ash is obtained with about 70% yield. These results are comparable to the maximum separation efficiency curves of washability studies on the coal samples. Since the ash percentage of coal particles collected in the bins close to positive and negative electrodes are about 70% and 20%, a better yield with further reduced ash content can be accomplished by recycling the material. Thus, the tribo-electrostatic method observed to be a promising dry coal preparation technique, where the present laboratory size separator needs to be scaled to plant level for commercial application.
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| 70. |
- Edelbro, Catrin
(författare)
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Strength, fallouts and numerical modelling of hard rock masses
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prediction of compressive stress-induced failures is of concern for the design and construction of deep underground excavations in mining and civil engineering. An overstressed rock mass may result in fallouts of rock, which may cause occupational safety hazards, damage of equipment, and/or production disturbances. The purpose of this thesis was to improve on how to model compressive stress-induced failure and fallouts with appropriate material models and strength parameters. The thesis focuses on commonly used design methods for underground excavation with special application to hard rock mass strength assessment. The aim was to suggest the most appropriate material model for fallout prediction and to identify factors governing the strength of hard rock masses. A comprehensive literature review of existing classification/characterisation systems and rock mass failure criteria used to estimate the rock mass strength was conducted. Existing rock mass failure criteria and classification/characterisation systems were evaluated through three case studies. A Round Robin Test was conducted for two of these cases. The evaluation was performed in order to identify robust systems and criteria, as well as to identify the parameters having the strongest impact on the calculated rock mass strength. The case studies revealed that the N, Yudhbir - RMR76, RMi, Q-, and Hoek-Brown - GSI methods, appeared to yield reasonable agreement with the measured stresses at failure. The parameters reflecting joint shear strength have a major influence on the estimated rock mass strength. The RMi method has proven difficult to use. For quality determination of the rock mass, a stress reduction free Q-system (or N) is preferable, as the Q-system covers a wider range of geological situations and the parameters are better described than for the RMR system. For massive rock masses in areas with high stresses and tight interlocks the impact of jointing is less obvious and the GSI method can be used for determination of the rock mass quality. In the subsequent work, a total of six selected case histories of fallouts in hard rock masses were studied. These were collected based on a comprehensive investigation and survey of well described compressive stress- induced fallouts, in drifts, raises and/or tunnels. All six cases considered civil and mining engineering rock excavations where the rock mass properties, measured stresses, behaviour and fallout were well documented. The field observations were compared with predictions from numerical modelling using the finite element analysis program Phase2. The results of the applied brittle-plastic models were sensitive to changes of the peak strength parameters and less sensitive to variations in residual parameters. A cohesion-softening friction-hardening (CSFH) model, using peak cohesion equal to the intact rock strength, proved to be the most appropriate material model for capturing the observed rock behaviour. Yielded elements failed in shear and intersecting shear bands were found to be good indicators of compressive-stress induced fallouts. This is likely since shear is often the final mechanism in the failure process before fallout occurs. The potential compressive stress-induced fallouts can, using a CSFH model, be predicted using the following indicators: (i) intersecting shear bands with significantly elevated strains and which connect to the excavation boundary, and (ii) shear bands being located within the region of yielding. Both criteria must be fulfilled simultaneously. The results showed that the developed shear bands and the zone of yielded elements were sensitive to changes in mesh density. By using small elements (0.01 m) at and close to the boundary of the excavation and in the region of the predicted failure, the results showed no significant changes of the predicted failure zone, with a further decrease in zone size. The CSFH model was applied for prediction and follow-up of compressive stress-induced failure and fallouts of footwall drifts in the Kiirunavaara underground mine. A multi-stage analysis was carried out in order 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. The modelling results were sensitive to the shape of the drift. The location of the predicted fallouts in the model was in good agreement with the location of observed fallouts for the case when the drift roof was simulated flatter than the theoretical cross-section. The results indicate that the true shape of the drift was different from the planned one. Simulating actual fallout by removing the indicated region of fallout in the model showed fewer occurrences of compressive-stress induced fallouts in later loading stages for footwall drifts in the Kiirunavaara mine. By scaling the damaged rock and creating a v-notch in the roof (similar to the predicted fall-out shape), in an access drift in the Kristineberg mine, the stability of the excavation was improved.
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