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Sublevel caving (SLC) is a highly productive mining method with the major disadvantages of irrepressible ore loss and dilution. The confined blasting situation of SLC rings is commonly regarded to have a significant impact upon the material flow characteristics and hence on the overall performance. The initial conditions for the ore flow after blasting are unknown, as both the blasted geometry and the fragmentation itself are normally hidden. However, when opening a new drawpoint and in hang-up situations an inspection of the actual conditions is feasible. For this purpose, a remotely operated 3D photogrammetry system was custom built and used to reconstruct the ring front and/or cavity as a geo-referenced mesh model with colour information. Various blasting situations have been observed and this allowed a deeper study of the i) broken geometry and height, ii) over- and underbreak and their effects on subsequently blasted rings, iii) interaction effects between adjacent holes/rings, iv) drilling accuracy based on identified boreholes and v) mapping of geological structures and their influence on the blast result. The capabilities of the 3D image acquisition system to evaluate the blasting results are demonstrated with an example, in which a series of blasts were surveyed. Monitoring under hang-up situations, has then revealed the actual effects from confined blasting and gravity flow related issues. The 3D photogrammetry system is now increasingly being used to study hang-ups. By revealing and quantifying hitherto inaccessible information, the system has proven to be a valuable tool in increasing the understanding of both SLC breakage and flow. Godkänd; 2012; Bibliografisk uppgift: CD-ROM; 20121112 (matwim)

Blasting in SLC (sublevel caving) takes place in a semi-confined situation. Blasted material swells while the caved material compacts, and also, to a lesser extent, fills parts of the void volume of the production drift. Several analytical and empirical models have been developed in the past. However, understanding of the interaction of semi-confined blasting conditions, SLC blast design and rock mass characteristics on rock breaking performance is rudimentary. Instrumentation of the blasted burden with various sensors and study of the dynamics of burden movement against confinement is therefore important. Such measurements are very scarce and thus different systems have been tested both in laboratory and in the field. Main focus was thereby the development of measuring equipment that could be scaled up to full-scale SLC blasting and installed behind the rings. In the field tests, blastholes were drilled in a pillar, parallel to a cross cut drift in the LKAB Kiruna SLC mine. The burden constraint was achieved either by filling the drift of 7.0 x 5.2 m (width x height) with rock masses or reinforcing the drift wall. The tests were instrumented with different redundant sensors, which were installed in holes drilled from a parallel cross cut. The most promising one was a concept, which combines the initial movement recorded by an accelerometer designed to minimize zero-shift with the final displacement recorded by a fibre photoelectric sensor (‘fibre-optic zebra gauge’). For the filled drift wall blasting test the maximum velocity varied between 16 - 32 m/s with a compaction in the range of 4 - 5 %. A gap was verified to exist between the intact pillar and the blasted material. By comparison, the velocity for the unconfined situation yielded a considerably increased velocity (42 - 47 m/s). In addition, ‘Blo-Up’, a component within the Hybrid Stress Blast Model (HSBM), was used to model the blasting results. The ob-jective was to show that reasonable predictions of fragmentation and burden movement under confined conditions can be made. An unconfined reference experiment was used to calibrate Blo-Up and forward predictions of the confined case were made. In both cases, Blo-Up accurately reproduced the burden velocity and displacement observed in the experiments. The suggested measurement concept could be used for further measurements of confined burden movement in filled drift wall blasting tests and under controlled situations. As mentioned the final objective is instrumentation of the burden in SLC production rings. Godkänd; 2012; 20121112 (matwim)

The testing method of rock toughness is proposed by the international society of rock mechanics (ISRM), but the results may be influenced by the test pieces, and the details of the crack propagation and the stress intensity factors are not clarified through the testing. Also the experimental test requires tedious works for the preparation of test specimen and economical responsibility. The present study aims to simulate numerically the rock toughness testing which is proposed by ISRM. For this purpose, the authors propose a numerical method which can simulate the experimental testing, and they show the propriety of the proposed method by comparing the results with the experimental and other numerical methods. At the same time, they clarify the details of crack propagation behaviors in rocks, and show the change of the stress intensity factors. The proposed method is based on the displacement-type finite element method, and several techniques are introduced to obtain accurate solution of the mechanical behavior near the crack-tip area.

Godkänd; 2010; 20101216 (ysko)

Nine cylinder tests for emulsion explosives in expanding Ø100/110 mm copper tubes are reported. The explosive recipe for pure emulsion respectively for blend of ANFO/AN-prills was formulated specifically for Swebrec:s test program. The primary goal was to verify earlier determinations of the explosive energy. In addition, recordings from streak camera and data from contact pins was evaluated for copper tubes 350 mm long and Ø60/72 mm filled with FOX12/TNT. The latter was cooperation between FOI- Swedish Defence Research Agency and Swebrec- Swedish Blasting Research Centre.The Gurney energy was calculated when the expansion velocity was almost constant i.e. at a volume of the explosives gases 7-8 times the original explosive volume. Expansion data for each explosive were fitted to the JWL- equation with help of a Matlab routine and the estimated JWL-parameters were used to calculate the detonation energy.Our conclusions, based on the measured data with Ø100/110 mm tubes are that there is no significant difference in the Gurney energy for the three explosives. The detonation energy increases somewhat with addition of AN/AN-prills, but the difference is small compared to the data scatter. This was basically the same results as for the earlier tests with similar emulsion explosives.The aim of the separate technique study with FOX12/TNT was to verify the contact pin data against streak camera data for two tests. The comparison shows that contact pin radial velocity data for the two shots agree well and that the streak recordings agree fairly well. The comparison of the two techniques shows that streak recordings give a 3-7 % lower radial velocity after approximately 30 μs. The two techniques can be a complement to each other. Nio cylinderförsök med detonerande emulsionssprängämne i expanderande Ø100/110 mm kopparrör rapporteras. Sprängämnesrecepten för ren emulsion och för inblandning av ANFO/ANprills har tagits fram tidigare speciellt för Swebrec:s olika försök. Det primära målet var att verifiera tidigare beräknade sprängämnesenergier. Dessutom har två tekniker, svepbildsteknik respektive punktvärden med kontaktpinnar, för mätning av expansionen, utvärderats för små kopparrör 350 mm långa och Ø60/72 mm fyllda med FOX12/TNT. Det senare var ett samarbete mellan FOI och Swebrec.Gurney-energierna har beräknats när expansionshastigheten var i det närmaste konstanta vilket inträffar när rörens volym är ca 7- 8 gånger den ursprungliga volymen. Expansionsdata har passats till en JWL-tillståndsekvation med hjälp av en iterativ procedur i Matlab och JWLparametrarna användes för beräkning av detonationsenergin.Slutsatsen, utifrån uppmätta data för Ø100/110 mm rör är att det inte finns någon signifikant skillnad i Gurney-energierna för de tre sprängämnena. Detonationsenergin ökar något med tillsatser av AN/AN-prills men skillnaden är liten jämfört med dataspridningen. Vi fick tidigare ungefär samma resultat för liknade sprängämnen.Den separata teknikstudien med FOX12/TNT syftade till att med 2 skott verifiera tidigare utförda mätningar med kontaktpinnar. Jämförelser av radiella hastigheter för skott 1 med skott 2 visar att kontaktpinnarna ger god repeterbarhet och rätt god repeterbarhet för svepbildstekniken. Jämförelse av mätteknikerna har visat att svepbildstekniken ger 3-7 % lägre radiell hastighet för de två skotten efter ca 30 μs. Teknikerna kan komplettera varandra. Godkänd; 2009; 20100426 (ysko)

Godkänd; 2007; 20070316 (dan930)

Sub-level caving (SLC) is classified as a mass mining method and there is increasing interest in its application world wide and under a very wide range of geotechnical environments. In terms of flow, the caved rock or debris at the interface first acts as a wave trap, which may reduce the fragmentation. Model scale tests are being made to understand the mechanisms of rock breakage and therefore fragmentation under relatively confined conditions. To minimize geometrical and geological effects, tests were conducted mainly on cylinders of magnetic mortar of size Ø140×280 mm and PETN cord with different strengths was used as explosive in a center hole, giving a specific charge between 0,2 and 2,6 kg/m3. The size distributions of the blasted material and the aggregate as well as the swelling of the cylinders have been measured. For the latter, a freezing-slicing method was developed. The results show that the confinement results in fragmentation being coarser when compared to that from free cylinders, and that the properties of the debris have a strong influence on the fragmentation and the swelling. Skivrasbrytning är storskalig brytningsmetod som mer och mer har blivit intressant runtom i världen. I fronten av brytningen, så blir kontakten mellan rasmassor och skivraskrans en vågfälla. Detta kan i sin tur påverka fragmenteringen. Modellförsök har gjorts för att förstå mekanismerna bakom detta fenomen. Genom att minimera de geologiska effekterna hos modellmaterialet, så har försök gjorts på cylindrar av magnetitbruk med dimensionerna Ø140×280 mm. Pentylstubin har varit det primära sprängämne och därav har den specifika laddningen kunnat varieras mellan 0,2-2,6 kg/m3. Styckefall och svällning har mätts vid varje laddningskoncentration med varierade egenskaper hos de omgivande massorna. Genom att frysa proven efter sprängning, så har svällningen längs efter provkroppen blivit möjliga att bestämma. Resultaten visar att egenskaperna hos rasmassorna har stort inflytande på svällning och fragmentering. Godkänd; 2007; 20070919 (dan930)

The Boliden Mineral's Aitik mine strives to increase the throughput of the primary mills, which requires a better understanding of the blast fragmentation. This article describes detailed fragmentation monitoring work of round, 4141-2. Structural mapping and core drilling, drilling and charging monitoring, VOD-measurements and blast filming were made. The blast fragmentation on the trucks was monitored automatically with Split Online and manually with Split Desktop. Four barrel samples were sieved to obtain the fines part of the fragment size distribution. The Desktop images had to be edited to avoid fragment splitting and merging errors. The Online images contained errors of many kinds and seem to be sensitive to light conditions; measured fragmentation during night-time was about 50% finer than during daytime. The data appear to be log-normally distributed. The average fragment size x50 became either 171±108 mm (Online) or 458±175 mm (Desktop) and the correlation between the online and desktop data is virtually non-existent. Suggestions are also made how to improve the quality of the data. At the end, a complete fragment size distribution down to 0,2 mm for round 4141-2 is constructed by the use of the x50- and x80-values from Split Online and Desktop and the sieved samples, using the Swebrec function. Godkänd; 2007; 20071011 (finn)

The Boliden Mineral's Aitik mine strives to increase the throughput of the primary mills, which requires a better understanding of the blast fragmentation. This article describes detailed fragmentation monitoring work of round, 4141-2. Structural mapping and core drilling, drilling and charging monitoring, VOD-measurements and blast filming were made. The blast fragmentation on the trucks was monitored automatically with Split Online and manually with Split Desktop. Four barrel samples were sieved to obtain the fines part of the fragment size distribution. The Desktop images had to be edited to avoid fragment splitting and merging errors. The Online images contained errors of many kinds and seem to be sensitive to light conditions; measured fragmentation during night-time was about 50% finer than during daytime. The data appear to be log-normally distributed. The average fragment size x50 became either 171±108 mm (Online) or 458±175 mm (Desktop) and the correlation between the online and desktop data is virtually non-existent. Suggestions are also made how to improve the quality of the data. At the end, a complete fragment size distribution down to 0,2 mm for round 4141-2 is constructed by the use of the x50- and x80-values from Split Online and Desktop and the sieved samples, using the Swebrec function. Godkänd; 2007; 20071011 (finn)

Styckefallskurvor från sprängning av tre bergarter i modell- och fullskala presenteras. Modellförsöken gjordes med Ø100-300 mm cylindriska prover laddade med pentyl. Pallsalvorna i Bårarp och hos Hengl bestod av en rad med 5-10 hål, salvorna i Vändletäkten hade fyra rader med åttiotalet hål. Berget i Bårarp består av en massiv, sprickfri granitisk gnejs medan de andra bergplintarna var genomsatta av sprickplan och sprängskador. Vanliga kommersiella sprängämnen användes i dessa pallsalvor. Det finns tre viktiga likheter i styckefallskurvorna, oavsett skala. Den första är att alla kurvorna beskrivs utomordentligt väl av Swebrec-funktionen [1]. Den andra är att i ett dubbelogaritmiskt diagram parallellförskjuts kurvorna uppåt när den specifika laddningen ökar, något som stämmer med en av NBC-begreppets grundsatser. Den tredje är att i detta diagram har kurvorna en materialberoende inflektionspunkt. För amfiboliten från Hengl ligger punkten vid ca 0,5 mm, för Bårarp-gnejsen vid 1,0 mm och för Vändle-graniten vid 1,5 mm. Tillsammans taget tyder dessa likheter starkt på att sönderbrytningsmekanismerna i modell- och fullskala har stora likheter, trots de olika sprängningsförhållandena. Styckefallet i modell- och fullskala skiljer sig också åt i viktiga avseenden. Det första är att beräkningen av den specifika laddningen q baseras på olika lossbrutna volymer och beror på antalet fria ytor, vilka visas påverka styckefallet. För det andra så är exponenten för medelstyckefallets x50 beroende av specifik laddning olika; ca. 1,1 i modellskala (x50 v 1/q 1,1) mot 0,8 i fullskala. För det tredje så förklarar Kuz-Ram-modellens beroende av laddningsstorleken Q (x50 v Q 1/6) inte mätta skillnader när q är lika i de två skalorna. Bergfaktorn A verkar också ha ett inbyggt storleks- eller skalberoende, vilket ger olika prognosresultat för försöken i Bårarp och i Vändle. Det finns vidare en skalskillnad mellan styckefallskurvornas lutning s50 vid medelstyckefallspunkten. Värdena på s50 i utförda försök stämmer väl med tidigare rapporterade värden. Krökningsexponenten b i Swebrec-funktionen kan följaktligen uttryckas som en funktion av de två övriga parametrarna, x50 och xmax som anger storleken på största sten. Det skal- eller storleksberoende hos styckefallet som finns i Kuz-Ram-modellens x50-ekvation omfattar alltså både Q, A och exponenten för q, den specifika laddningen. För att förbättra ekvationen blir det troligen nödvändigt att vidga definitionen på specifik laddning. Godkänd; 2007; 20071012 (finn)

Godkänd; 2006; 20061211 (ysko)

Sprängförsök har utförts vid Swerock AB:s Vändletäkt för att ta fram en beskrivning av hur sprängningsresultatet kan påverkas så att önskat styckefall in i förkrossen erhålls. Resultatet blev bl a designkurvor som beskriver hur styckefallsfördelningen ändras när den specifika laddningen ändras. I två produktionssalvor krymptes hålmönstret i ena halvan och glesades ut i den andra med användning av befintlig borrutrustning. Uppföljningen bestod av profil- och hålinmätning, mätning av laddad mängd och VOD samt styckefallsmätningar mm. Ur salvorna togs fyra provhögar och ca 100 ton ur varje siktades och utvärderades med bildanalys. Materialet lades sedan tillbaka och provhögarna krossades medan krossningsenergin mättes. Ur siktdata kunde styckefalls-fördelningarna konstrueras med hjälp av Swebrecfunktionen. Några slutsatser är att - Styckefallet liknar bergmaterialkurva nr 62 - Sprängningen och förkrossen bidrar med lika mycket var av producerad bärlagerfraktion - Skutandelen kan uppskattas med bildanalysen men styckefallskurvorna från bildanalysen har annan form än siktkurvorna - Siktkurvorna bedöms vara tillförlitligare Godkänd; 2006; 20070105 (ysko)

Godkänd; 2006; 20061219 (ysko)

The paper presents a new particle size distribution function, called the Swebrec function discovered during the work with the EU project Less Fines project. The function has just three parameters, with physical meaning, in its basic form. Yet it covers a size range of 2­3 orders in magnitude of fragment size and even more in an extended version. It has been tested on hundreds of sets of sieving data from different kinds of blasting and crushing of many different kinds of rock. The coefficient of determination r2 has in 95 % of the cases been better than 0.995, many times substantially better. Examples of such curve fits are given and the relation of the Swebrec function to traditional comminution concepts like the NBC concept, the t10 concept and the GGS-slope will be pointed out. Applications such as an extrapolation from the coarse range to the fines and vice versa will be shown and as will how the Swebrec function could be used to construct the fragment size distribution for muck piles from full-scale blasts, based on limited data. A final remark on how to implement the Swebrec distribution into fragmentation models will be given. Validerad; 2006; 20061221 (ysko)

The blasting at the Vändle aggregate quarry has been investigated in order to predict the effect of the specific charge on fragmentation and to assess the contribution of blasting and primary crushing to the -32 mm fines. Two 25000 ton blasts divided into halves were monitored. Each half had an expanded or a shrunken pattern in order to lower or raise the specific charge. A normal round uses Ø90 mm drill-holes on a 34 m pattern with a gassed bulk emulsion blend with 20-25 % of AN prills. The test rounds lay directly behind each other, with a shrunken pattern behind an expanded one and vice versa to minimize the influence of geology.From the muck piles, four test piles of about 500 tons were extracted and photographed for image processing. About a quarter of each was sieved in four steps and fines samples taken. The material was replaced and the whole pile fed to the primary crusher while measuring the effect and the fines produced. Crushability and grindability data were measured.All lab samples and crushing test samples follow the new Swebrec distribution extremely well. The fragmentation size distribution of the muck piles is constructed using the sieving data and the lab samples, conforming to the Swebrec function. Image analysis gives a fragmentation curve with a distinctly different character. Of the total of 28 % of -32 mm fines after primary crushing, blasting and crushing contribute about half each. Based on these data a set of design curves are constructed that allow the prediction of how any given fraction changes when the specific charge in the round is changed. Godkänd; 2006; 20061208 (ysko)

Hur ser styckefallet ut efter sprängning? Gamla fördelningar blir oftast helt missvisande beträffande finandelen. Den nya "Swebrec-fördelningen" löser detta och återger det siktade styckefallet oerhört väl inom området 1-500 mm. Fördelningen har 3 parametrar, medelstyckefallet xso, största stenstorlek xmax och en kurvparameter b. Samma fördelning visar sig även beskriva krossat berg utomordenligt väl. Utöver den bättre återgivningen av styckefallet så kan fördelningen också användas till att ur prov på finandelen i en salva uppskatta hela styckefallsfördelningen eller att ur grovdelen uppskatta finandelen.Siktade försöksdata från alltifrån sprängning av laboratorieprov till fullskalesprängning visar att fördelningens tre parametrar följer ett generellt samband. Denna information kan användas till att ta fram en helt ny fragmenteringsformel. Den kan också användas till att utgående från faktiska driftsförhållanden förutsäga hur mycket medelstyckefallet skall förändras för att ge den önskade förändringen av en given fraktion, Lex. bärlager material -32 mm. Godkänd; 2005; 20070105 (ysko)

Godkänd; 2005; 20070215 (ysko)

Godkänd; 2005; 20070215 (ysko)

Rock fragmented by blasting follows a different size distribution than the commonly used Rosin-Rammler distribution, especially in the fines range. Sieving data from many different blasting operations have led to a new distribution function, which can describe the fragmentation over the range 1-500 mm quite accurately. It is called the Swebrec© function and works also for crushed rock. It contains three parameters, the median fragment size x50, the maximum fragment size xmax and an undulation parameter b, which is shown practically to be a function of the other two. The fit to the sieved data is often , which is shown practically to be a function of the other two. The fit to the sieved data is often better than r2 = 0.995 over 2-3 orders of magnitude of fragment size. The Swebrec function could be used to estimate the complete size distribution from a sample in the fines range or the fines tail from coarse range data. It is used to construct a blast fragmentation model, the KCO model, which improves greatly on the Kuz-Ram model. In a first application it is shown how, in a given production situation, it is possible to predict the change in average fragmentation that is required to increase (or decrease), for example, the road base fraction 0-32 mm in the muckpile by a desired amount. Godkänd; 2005; 20061208 (ysko)