No description available.

It is important that the society is functional in the case of a crisis or war. In these cases, some social functions are more important than others and should be prioritized according to MSB (2014). Management and coordination of social actors are extra important in these situations, and this is where the function of operations rooms becomes important. The purpose of this master thesis is to describe how the function in the operations rooms should be maintained despite fire outside the room in the facility. The thesis includes operations rooms for military, municipalities, county councils, county administrative boards and authorities, as well as emergency rescue services. To ensure that the command function can be maintained, the outer structure is dimensioned for a fire according to ISO 834 for 12 hours. The technical and personal supply is dimensioned to maintain the function for 10 days. As a result of this, the outer wall is dimensioned to 400 millimetres which leads to a zero heating of the room and 260 millimetre wall that maintain 80 percent of the carrying capacity. To maintain the technical support, a diesel engine is designed to meet the energy needs. As a conclusion, this work chart the conditions for a room that offers a shelter from a fire and maintain a management function. These facilities are complex and each underground facility must be dimensioned separately.

No description available.

Luossavaara-Kiirunavaara AB (LKAB) is an iron ore mining company in Sweden that strives to be one of the leading suppliers of iron ore products. In the chain from mining to end customers, transportation efficiency plays a mayor role in the outcome of the company's total financial result. The transportation of the ore from the LKAB mines in Kiruna and Malmberget is made by trains to the harbors in Narvik and Luleå. The railway transportations are made by LKAB subsidiaries Malmtrafik i Kiruna AB (MTAB) on the Swedish side and Malmtrafikk AS (MTAS) on the Norwegian side. The efficiency of the railway transportation is therefore a key function in the LKAB mining operations. In a benchmarking, comparing the total operating efficiency, with other heavy haul railways around the world it became evident that the efficiency of the railway transportations at LKAB had potential for improvement. One of the factors with potential for improved efficiency was the maintenance strategy. There is an indication that a change from a time-based maintenance strategy to a condition-based maintenance strategy would increase the efficiency of the train operations. The purpose of this thesis is to study and analyze wayside condition monitoring equipment for railway vehicles, in order to support the implementation of a condition-based maintenance strategy. To fulfill the stated purpose, five case studies, supported by a literature study, have been performed. The five case studies have been conducted to increase the knowledge of the abilities of available wayside condition monitoring equipment as a support for condition-based maintenance of railway vehicles. The literature study focused on railway operations around the world with a particular focus on the development, deployment and use of wayside condition monitoring equipment. The literature study indicates that there is an increasing implementation and use of equipment for wayside condition monitoring of railway vehicles. Through the studies it has become evident that the direct interaction in the wheel and rail interface also creates a huge potential for savings on the infrastructure due to an implementation of wayside condition monitoring equipment for railway vehicles. The case studies highlight the need for different systems that complement each other by measuring different parameters. It is also important that the systems are integrated with existing systems and practices in order to exploit the potential benefits of the new technology. Furthermore, it is important to have a joint approach between both infrastructure owners and train operators in the deployment and use of wayside condition monitoring equipment, since the technology can support a condition-based maintenance strategy on both sides that could have a great impact on the efficiency of railway operations. / Luossavaara-Kiirunavaara AB (LKAB) är ett Svenskt gruvbolag som bryter järnmalm. Man har som målsättning att bli en av de ledande leverantörerna i världen av järnmalmsprodukter. I kedjan från brytning till slutkund, spelar transporteffektivitet en avgörande roll i företagets totala ekonomiska resultat. Transporterna av malm från LKAB:s gruvor i Kiruna och Malmberget utförs med järnvägstransporter till utskeppningshamnar i Narvik och Luleå. Järnvägstransporterna utförs av LKAB:s dotterbolag Malmtrafik i Kiruna AB (MTAB) på den Svenska sidan och av Malmtrafikk AS (MTAS) på den Norska sidan. Järnvägs transporternas effektivitet är därför en nyckelfunktion i LKAB:s gruvbrytningsverksamhet. I en benchmarkingstudie utförd på den totala effektiviteten av verksamheten hos gruvverksamheter med tunga järnvägstransporter runt om i världen blev det uppdagat att det finns en potential att förbättra effektiviteten hos LKAB:s järnvägstransporter. En av faktorerna som har potential att förbättra effektiviteten är underhållsstrategin. Det finns tydliga indikationer på att en förändring från ett förutbestämt underhåll till ett tillståndsbaserat underhåll skulle kunna öka järnvägstransporternas effektivitet. Syftet med denna licentiat avhandling är att utvärdera tekniska system som kan placeras vid spåret och användas som tillstånds övervakande utrustning för järnvägsfordon för att stödja en implementering av en tillståndsbaserad underhållsstrategi.För att uppnå det utsatta syftet har fem fallstudier, samt en litteratur studie genomförts. De fem fallstudierna har utförts för att öka kunskapen om egenskaperna hos tillgänglig tillståndsövervakande utrustning för placering vid spåret som stöd för tillståndsbaserat underhåll av järnvägsfordon. Litteraturstudien har fokuserats på järnvägsverksamheter i runt om i världen med speciellt fokus på utveckling, utplacering och användande av spårbunden tillståndsövervakningsutrustning .Litteraturstudien indikerar att det pågår en ökande implementering och användning av tillståndsövervakande utrustning för järnvägsfordon. Genom studierna har det framkommit att den direkta interaktionen mellan hjul och räl också skapar en stor potential för besparingar på infrastrukturen med hjälp av en implementering av spårbunden tillståndsövervakande utrustning för järnvägsfordonen.Case studierna belyser nödvändigheten av att ha olika system som kan komplettera varandra genom att mäta olika parametrar. Det är också viktigt att systemen är integrerade med existerande system och metoder för att uppnå de potentiella fördelarna med den nya teknologin. Det är dessutom viktigt att ha ett gemensamt tillvägagångssätt mellan både infrastrukturägare och tågoperatörer i implementeringen och användandet av spårbunden tillståndsövervakande utrustning, eftersom teknologin kan stödja en tillståndsbaserad underhålls strategi för båda sidor, vilket kan ha stor positiv inverkan på järnvägsdriftens effektivitet. / <p>Godkänd; 2007; 20070315 (ysko)</p>

Rail infrastructure is a large and costly investment, and has a long life. To realize the benefits from this investment, effective maintenance is required. Railways are one of the prime modes of transportation in many countries and as they are closely associated with passenger and cargo transportation, they own high risk in terms of potential loss of human life and damage/destruction of assets. New technologies and stringent safety standards are constantly being introduced, but accidents still occur. There will always be some risk associated with derailments and collisions, but it can be reduced by elimination of the root causes by means of an effective maintenance strategy to govern optimization of inspection, lubrication and grinding frequency and/or improvement in skill and efficiency. A detailed study of the defects which emerge both in the rolling stock and the rail infrastructure is essential to identify the correct maintenance strategy. Detection and rectification of rail defects/degradations are major issues for all rail players around the world. Some of the rail degradations include worn out rails, weld problems, internal defects, corrugations and rolling contact fatigue (RCF) initiated problems such as surface cracks, head checks, squats, spalling and shelling. If undetected and/or untreated, these defects can lead to rail breaks and derailments. Efficient maintenance strategies can reduce potential risk of rail breaks and derailments. A potential risk is the risk which accumulates in the form of rail degradation over a period of time. In spite of continuous efforts made by all rail infrastructure operators around the world to reduce costs, a substantial proportion of railway budget is spent on rail maintenance. It is understood that the consequential costs due to derailment reduces with increase in inspection, lubrication, grinding and replacement costs. The challenge is to find a balance between the maintenance costs which consists of inspection, lubrication and grinding costs, and consequential costs due to derailments. The consequences of derailment in terms of loss of human life, damage/destruction of assets and loss of company trust and reputation justify maintaining stringent safety standards, which require massive rail maintenance investments in order to be met. Reduction in maintenance investments may increase the rate of rail degradation, which may increase the risk of derailments. The aim is to develop an approach to predict rail failures, which will help to optimize maintenance activities (inspection, grinding, rectification/replacement and/or welding). Generally, there is a trade-off between maintenance investment and the risk involved in rail degradation in order to develop a rail maintenance procedure. Failure prediction of rail sections undergoing degradation will help to estimate the risk of derailment. Thus, prediction of the rail failure rate is a requirement for the development of an effective rail maintenance procedure. Different types of rail degradation processes leading to various rail defects have been studied. The performed literature studies indicate a need for better prediction of rail failure over a period of time based on the factors influencing rail degradation. The maintenance strategy followed by the Swedish National Rail Administration (Banverket), Sweden's rail infrastructure operator, is described and the issues related to rail degradation and maintenance are outlined for further research in this area. Rail failure data has been extracted from different Banverket's databases, classified according to a classification framework developed and analyzed over a period of time based on Million Gross Tonnes (MGT) of traffic using Weibull distribution. During the process of data evaluation and analysis, a method of extracting useful information from incomplete data has been identified. / <p>Godkänd; 2006; 20061212 (ysko)</p>

This thesis is based on a case study of the Kiirunavaara sublevel cave (SLC) mine. It focuses on footwall stability and damage development in the mining infrastructure on mine scale. Damage to the infrastructure is mappable for the full height of the footwall by access through decommissioned infrastructure associated with earlier mining stages. Damages range from pure structurally controlled failures (wedge failures) in the upper part of the footwall to fracture growth through intact rock combined with micro‑seismic emissions at the active mining depth. The thesis addresses four distinct research questions; (i) What are the predominant failure mechanisms for the Kiirunavaara footwall? (ii) What is the role of confinement on the damage development in the footwall? (iii) How does the SLC relate to the footwall damage development? (iv) How can infrastructure damage associated to the future mining be estimated using currently available data? Two sets of calibrated numerical models were used to study the damage evolution processes using damage mapping data as the main calibration parameter. Validation of the models was achieved by correlation of model output to micro-seismic locations. The modelling and damage mapping results were used as the basis for the development of a simple prognosis tool for estimating the ultimate extent of infrastructure damage associated to the mining advance for future mining steps. A literature review on slope failure modes, large scale failures in cave mining and failure tracking using micro-seismic locations is included to provide background and definitions. The literature describes principal failure modes as well as mechanism combinations such as structurally controlled failures initiated by deep seated rock mass failures or relaxation. Cases are presented where previously stable structures become destabilised by cave advance and examples where micro‑seismic recordings were used to track deformations and the initiation and growth of newly formed fractures. The Kiirunavaara SLC mine is presented in detail as the main case study of the work. The mine has been in operation since the early 20th century with a transition to underground operation over 50 years ago. The extent of the orebody is 4 km in length with an average width of 80-90 m, the termination at depth has yet to be determined. The ore has an average dip of 60˚ east and a dip-along-strike to the north. Both the footwall and hangingwall rock masses are considered hard and competent with UCS values for the footwall ranging from ca. 130 MPa to extreme cases of 600 MPa. The ore is mined in production blocks about 400 m wide (along strike), Mining of the northernmost blocks, situated in the Lake ore, did not start as open pit operations but has been accessed from the underground via SLC only. The instabilities in the footwall has been addressed by several research studies in the past, with the predominant failure mechanisms in different studies being suggested as large scale tensile failure, complex wedge failure, or rotational shear failure, i.e., some type of principal slope failure. In this work, conceptual numerical models in UDEC were calibrated to fit underground damage mapping data by tracking numerical shear strain concentrations. The conceptual models suggested rock mass damage without the indications of development of large scale slope failure mechanisms such as shear bands. Mine scale PFC models were calibrated with respect to the rock mass strength parameters derived by the conceptual UDEC models and used to study rock mass fracturing in the absence of large scale failure. It is shown that damage to the rock mass occurs mainly close to the active mining in a seismically active zone. This is suggested to weaken and soften the rock mass to allow the development of infrastructure damage in this volume to occur as the rock mass relaxes when entering the stress shadow of the SLC as mining progresses. The damage to the rock mass at the production depth is argued, based on seismic records and a parametric study in UDEC, to constitute of large quantities of local shear failures coalescing to appear as a large scale step-path or rotational shear failure in mapping records. The extent of the associated infrastructure damage is predicated to be limited by the extent of the damaged rock mass zone. A simple bi-linear equation is suggested using ore-width and mining depth as input to estimate the ultimate extent of the damaged zone for each mining stage and thus the limit of later infrastructure damage development. The thesis is concluded with recommendations for future work and potential for continued research. / Denna avhandling baseras på en fallstudie av skivrasgruvan Kiirunavaara. Fokus ligger på liggväggstabilitet och skadeutveckling på gruvans infrastruktur i gruvskala. Infrastrukturskador kan karteras längs med hela liggväggens höjd där tillgång till bergmassan ges via urdrifttagna ortar och ramper drivna i samband med tidigare brytningssteg. Dokumenterade skador varierar med djupet – från strukturstyrda brott i den övre delen av liggväggen till ny sprickbildning genom intakt berg kombinerat med mikro-seismik vid nuvarande brytningsdjup. Fyra distinkta forskningsfrågor avhandlas; (i) Vilka är de dominerande brottsmekanismerna i Kiirunavaaras liggvägg? (ii) Vilken roll spelar inspänning för brottsutvecklingen i liggväggen? (iii) På vilket sätt relateras skivrasbrytningen till brottsutvecklingen? (iv) Hur kan skador på gruvans infrastruktur kopplat till framtida brytningssteg uppskattas med data tillgängliga idag? Två omgångar med kalibrerade numeriska modeller togs fram för att studera skadeutvecklingen i liggväggen med skadekarteringsdata som primär kalibreringsparameter. Validering av modellerna uppnåddes genom att studera samstämmigheten mellan modellresultaten och lokaliseringen av mikro-seismiska händelser. Modellresultaten och skadekarteringsdatabasen användes som grund för att utveckla ett enkelt prognosverktyg för att uppskatta den slutgiltiga utbredningen av infrastrukturskador direkt associerade med gruvbrytningen för framtida brytningssteg. En litteraturstudie av släntbrott, storkskaliga brott i samband med rasbrytning samt brottsövervakning med mikro-seismik är inkluderad som bakgrund och för att definiera terminologier som används genom avhandlingen. Literaturstudien beskriver principiella brottsmekanismer samt kombinationer av mekanismer såsom strukturstyrda brott pådrivna av djupt belägna bergmassebrott eller minskad inspänning. Fallstudier presenteras där tidigare stabila strukturer destabiliseras av rasbrytningens framskridande och exempel där mikro-seismikdata använts för att följa deformationer samt initiering och tillväxt av nya sprickor i intakt berg och bergmassa. Kiirunavaaragruvan presenteras i detalj som den huvudsakliga fallstudien för arbetet. Gruvan har varit aktiv sedan tidigt 1900-tal med övergång till underjordsbrytning för över 50 år sedan. Malmkroppens utbredning är 4 km längs strykningen med en genomsnittlig vidd av 80-90 m, och malmkroppens fortsättning mot djupet är öppen. Malmen har en genomsnittlig stupning av 60 grader öst med en fältstupning mot norr. Bergmassan i både liggvägg och hängvägg anses vara hård och kompetent med UCS värden för liggväggen mellan ca. 130 MPa till extrema fall av 600 MPa. Malmen bryts i produktionsblock med ca 400 m bredd (längs malmens strykning). Brytning av de nordligaste blocken, belägna i Sjömalmen, har inte skett i dagbrott utan har utförts enbart via skivrasbrytning. Instabiliteten i liggväggen har avhandlats i ett flertal tidigare studier. De dominerande brottsmekanismerna har föreslagits i tidigare arbeten som storskaligt dragbrott, komplext kilbrott eller cirkulärt skjuvbrott d.v.s. någon typ av principiellt släntbrott. I arbetet för denna avhandling kalibrerades konceptuella numeriska modeller i UDEC mot skadekarteringsdata från liggvägens underjord, med avseende på koncentrationer av skjuvtöjningar. De konceptuella modellerna visade på bergmasseskador utan indikationer på storskaligt släntbrott, exempelvis koncentrationer av numeriska skjuvband. PFC-modeller i gruvskala kalibrerades gentemot bergmasseparametrarna från de konceptuella studierna i UDEC för att direkt studera upprickningen av bergmassan i frånvaro av storskaliga brottsindikationer. Modellerna visade på att skador i bergmassan främst uppkommer nära brytningsområdet i en seismiskt aktiv zon. Detta föreslås försvaga och mjukgöra bergmassan vilket i sin tur leder till utveklingen av infrastrukturskador i den skadade volymen när berget avlastas då området hamnar i spänningsskugga från skivraset. Ovanstående studier visar att skadorna som uppkommer i bergmassan, baserat på de konceptuella UDEC-modellerna och mikro-seismiska data, består av ett stort antal lokala skjuvbrott vilka samverkar till att framstå som ett storskaligt trappstegsbrott eller cirkulärt skjuvbrott i skadekarteringsdatat. Utbredningen av de relaterade infrastrukturskadorna förutspås begränsas av utbredningen av bergmasseskadorna uppkomna vid bryningen. Ett enkelt bi-linjär samband föreslås vilket använder malmbredd och brytningsdjup för att uppskatta den slutgiltiga utbredningen av skadezonen i bergmassan för varje brytningssteg, och i förlängningen begräsningen av senare uppkommande infrastrukturskador. Avhandlingen avslutas med rekommendationer för fortsatt arbete samt framtida forskningspotential.

In coming decades, many underground mines will operate at greater depths, which will affect many operational factors such as increased rock stress, longer haulage distances, and higher energy consumption, which potentially can generate lower production rates. The increased rock stresses may lead to smaller sized openings, further restricting the size of loading and hauling equipment that can be used. Longer hauling distances result in increased energy consumption for loading and hauling equipment, and in turn, high energy consumption increases heat and gas emissions for diesel equipment. Heat emission increases ventilation costs as large volumes of air must be circulated to cool diesel engines and simultaneously maintain adequate air quality for personnel.The research presented in this thesis was carried out to evaluate and analyze different haulage systems, including diesel and electric trucks, shafts, and belt conveyors. The aim was to determine how these various material-handling equipment may produce the desired production objectives and lead to lower energy costs. The net present value (NPV) of the mine plan at increasing mining rates and altered commodity prices was also analyzed. The method used was the combination of discrete event simulation and mixed integer programing. Discrete event simulation was used to estimate mine production for different haulage systems, and the results were used to compute appropriate mining costs for each hauling option. Mixed integer programming (MIP) was then used to generate the optimal production schedule and mine plan. The analysis showed that an increasing use of electric trucks will have positive effects on production improvement because electric trucks have shorter cycle times than their diesel counterparts. Therefore, electric trucks can make more cycles than diesel trucks in the same period of time. The analysis also showed that low-profile equipment will remain viable for haulage in high stress environments that result in smaller sized mine openings. In addition, when friction hoist systems are used, rope speed and skip payload play important roles in production improvement. With belt conveyors, production improvements can be obtained by increasing surcharge angle and running the belt at a low speed. For long hauls, the troughing angle should be increased and the belt operated at a higher speed.Energy costs increase with depth and are higher for diesel trucks compared with other haulage options. At 1000-meter depths and with current energy prices, energy costs for diesel trucks, electric trucks, belt conveyor, and shaft account for 62%, 54%, 25%, and 14% of the total haulage costs, respectively. These findings indicate that minimizing the usage of diesel engine machines will have greater benefits towards cost reductions in an era of increasing energy prices and greater mine depths. Diesel machines also have high heat and gas emissions, which increases operating costs particularly for deeper mines where heat emissions increase ventilation costs.Changes in mine plans based on changing commodity prices at a fixed mining rate resulted in an increase in the NPV from $96M to ultimately $755M for the studied case. An increase in mining rate from 300,000 to 450,000 tonnes raised the NPV to $773.45M. This finding indicates that even though an increase in mining rates increases costs, companies may find that pursuing such a course is beneficial at certain commodity prices, especially when the price is elevated. When the price falls, increasing mining rate may need a detail evaluation of other parameters such as grade, recovery, and investment changes.The evaluation showed that the method of combining discrete event simulation and mixed integer programming can yield a feasible solution and better understanding of the operational systems and reduce risks in selecting a system before it is implemented. This study provides mining companies an analysis of the use of underground haulage systems that can aid decision making. / Godkänd; 2014; 20141021 (abusal); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Abubakary Salama Ämne: Gruv- och Berganläggningsteknik/Mining and Rock engineering Uppsats: Haulage System Optimization for Underground Mines Opponent: Professor Jazek Paraszczak, Université Laval, Canada Ordförande: Professor Håkan Schunnesson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Torsdag den 27 november 2014 kl 10.00 Plats: F1031, Luleå tekniska universitet

Degradation is an on-going process in systems, equipments and components subjected to various stresses and adverse operating conditions. The factors influencing the degradation process may adversely affect the system or component performance. A study of these factors will provide a basis for making correct decisions concerning corrective and preventive measures. Such a study is also useful for reliability analysis of the degrading systems/components for making maintenance decisions or for initiating measures for changes in the design. Many times it is not possible to implement design changes due to complexities and cost considerations, as in the case of railway infrastructures, etc. In such situations operational reliability is assured through effective maintenance actions. Knowledge of the technical condition of components is important to achieve the optimal maintenance policy in order to minimize the total system risk. A methodology for rail defect prioritization and risk assessment is developed to support the decision- making process during the effective scheduling of the inspection frequency based on the type of defect and its risk of developing into a rail break. The present research work also demonstrates an application of reliability analysis to improve system reliability based on design changes. This has been illustrated with an example from a manufacturing industry. The objective is achieved using cost-benefit analysis in combination with failure data and root cause analysis. The analysis of failure data with the different cost elements involved in the operation and maintenance of the complex systems is presented as a basis for choosing between alternative designs. Furthermore, an optimization model has been developed to estimate the optimum inspection frequency required at the minimum maintenance cost based on the technical condition of the component. The model has been validated by a case study of an offshore oil and gas platform. The consequences of not choosing the right distribution have also been discussed in the thesis. The concept of the virtual failure state has been introduced to estimate the failure distribution of highly critical components. The factors influencing the degradation process have been identified and studied in detail. A framework for classification of rail failure data has also been developed for rail life estimation using reliability analysis. In short, the thesis discusses the application of reliability analysis and cost modeling techniques to support the decision-making process in operation and maintenance activities and demonstrates its usefulness in real life. / Godkänd; 2008; 20080328 (ysko)

All businesses need equipment to deliver services or manufacture goods. Over time, this equipment will degrade, but with proper maintenance, the degradation can be controlled, and failed equipment can be restored to operational status. Run-to-failure maintenance is performed when equipment or systems break down. In preventive maintenance, equipment is maintained as a precautionary measure to prevent failure. Finally, condition-based maintenance recommends maintenance actions based on the condition of the asset.The railway is a superior mode of transport if capacity, speed and environment are the main criteria; it also plays a crucial role in heavily crowded regions. The condition of the wheels and the rails affects rail- way safety, and infrastructure regulators and managers are always trying to reduce potential risk areas. The wheel-rail interface triggers most of the cost for maintenance.The railway wagons in this research use a time-based maintenance strategy, a strategy which does not fully consider the actual health of the asset. However, by using condition data from observations, along with diagnostics and prognostics, an effective condition-based maintenance strategy can be planned effectively way and executed efficiently.The results of this research suggest the efficacy of using automatic condition monitoring systems to increase the amount of available data for analysis and maintenance support planning, rather than depending on a system where operators or maintenance personnel do the measurements. The results also indicate that continuous monitoring of lateral forces will decrease the risk of derailment.Condition monitoring data can support maintenance preparation, assessment, and improvements and help to form a continuous improvement loop. This, plus a condition-based maintenance strategy, will lead to capacity assurance. / Godkänd; 2014; 20131125 (mikpal); Tillkännagivande disputation 2014-01-07 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Mikael Palo Ämne: Drift och underhållsteknik/Operation and Maintenance Avhandling: Condition-Based Maintenance for Effective and Efficient Rolling Stock Capacity Assurance A Study on Heavy Haul Transport in Sweden Opponent: Professor Doug Hargreaves, Science and Engineering Faculty, Queensland University of Technology, Australia Ordförande: Professor Uday Kumar, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Måndag den 3 februari 2014, kl 10.00 Plats: C305, Luleå tekniska universitet

Impact-loaded conical and cylindrical friction joints are studied theoretically and experimentally. The system considered consists of a long, straight, cylindrical and linearly elastic rod which is impacted axially at one end, and which has a body attached by means of a friction joint at the opposite end. The conditions are such that the wave propagation is 1-D in the rod and can be neglected in the attached body. Slip and energy dissipation due to an impact load are determined. The theoretical results of the impact-loaded conical friction joints exhibit phenomena which sometimes have spectacular appearance. The agreement between theoretical and experimental results is fair. The influence of blow frequency and thrust on the performance of a percussive rock drill is studied theoretically. The drill considered consists of hammer, adapter, rod and bit. Two different rock drills are studied. The first is a simple drill with constant characteristic impedance throughout the drill. The second is a prototype of a high frequency percussive rock drill. The efficiency and the maximum (maximum tensile) and minimum (maximum compressive) stresses are determined. For the simple drill the average efficiency in the range from soft to hard rock is only weakly dependent on the blow frequency up to relatively high blow frequencies but strongly dependent for extremely high blow frequencies. It is also found that the maximum and minimum stresses in the drill in the range from soft to hard rock are only weakly dependent on the blow frequency up to high frequencies but strongly dependent for extremely high frequencies. The maximum stress increases and the minimum stress decreases with thrust. / Godkänd; 1986; 20070108 (mlk)