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The dynamics and fragmentation of blasted ore slices in scaled sublevel caving and slab models followed by accuracy analysis of the "Volume weight method" used for determination of ore content at loading
KTH. (Division of Minin)
2013 (English)In: Rock Fragmentation by Blasting, FRAGBLAST 10 - Proceedings of the 10th International Symposium on Rock Fragmentation by Blasting, 2013, 357-371 p.Conference paper (Refereed)
Abstract [en]

The sublevel caving mining method is described in the introduction. The problem in sublevel caving is if the swelling and fragmentation of the ore is not enough, then the mobility of the ore will be too low so the main mass can not move only the smallest pieces created in the vicinity of the blastholes will move downwards by gravity forces. The hypotheses tested in this project was therefore, if we by model tests can study the dynamics of the blasted ore and thereby learn the kinematic in detail and get a better understanding of the swelling of the ore and finally be able to make better blast designs for the full scale mine to avoid freezing of the ore. A second objective was to examine if the "Volume weight method" could be used to determine the cut off point when loading the ore waste rock mixture. The research strategy developed was to simulate full scale blasting as geometrical and accurately as possible and to use the smallest possible scale thereby reducing the cost of model material and material handling. The blastholes were charged manually with dry and fine grained PETN explosive and initiated by precise Micro Second Ignition Beams. Within the burden, in one SLC Normal Profile model, numbered markers were placed in three vertical planes before casting of the model. The model material consisted originally of magnetite concrete, but joints were lacking in these models and had to be introduced to achieve a scaled fragmentation. The introduction of crushed microscopic glass for simulation of joints worked very well and the amount of wished middle size fractions increased considerable. Special made plastic markers were used for the observation of the movement of ore during initial blasting and during loading of the blasted ore. A new technique for creation of the blastholes was developed by insertion of oiled iron bars before casting so they could be removed after the curing of the model. The movement of the burden was recorded for 1 SLC Silo Profile model by a high speed camera in a section representing a vertical cut along the loading cross cut.The fragmentation size distribution and the ratio of weight of ore to weight of caved waste rock was determined at different extraction levels. The swelling, velocity and the acceleration of the burden against the caved rock was also measured in the Silo model. In 6 Slab blasting models the influence from delay time on the fragmentation of ore was studied. The optimal delay time was 0,1 ms. At 0 and 0,005 ms delay time the linear swell was negative. The result shows generally a higher positive linear swell in the middle of the round compared to the sides. The maximum mean linear swell was 42% of the burden at 0,1 ms delay time. In the SLC Normal Profile models the swelling of ore into the drift was recorded with the help of plastic tube markers, 10 mm in length. Most early markers comes from the area close to the blastholes which is well fragmented. Regarding the Volume weight method the maximum error between real and calculated ore content using the volume weight method was 23 weight-%. The standard deviation of the difference for 24 extracted unit volumes (Kiruna trucks) was 12 weight-%. Quantification of all parameters studied was possible in 12 Slab models, 12 Normal Profile models and 2 Silo models. This kind of modelling developed can therefore be recommended for future research.

Place, publisher, year, edition, pages
2013. 357-371 p.
Keyword [en]
Blasting, Fragmentation, Gravity flow, High speed camera, Loading of ore, Measurement method, Model test, Ore content, Ore dilution, Sublevel caving, Swelling, Volume weight method, Gravity flows, Measurement methods, Model tests, Dynamics, Explosives, Gravitation, High speed cameras, Ore analysis, Ore treatment, Ores, Rock bursts, Loading
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-117832ScopusID: 2-s2.0-84869169101ISBN: 978-041562143-4OAI: diva2:603857
10th International Symposium on Rock Fragmentation by Blasting, FRAGBLAST 10, 24 November 2012 through 25 November 2012, New Delhi

QC 20130207

Available from: 2013-02-07 Created: 2013-02-05 Last updated: 2013-02-07Bibliographically approved

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