Element methods (FEM and BEM) have been used to prepare a stopping plan for the Kotalahti nickel mine. The rock mass between levels +600 and +800 is of poor to fair quality. Maximum horizontal stress is about 50 MPa acting in an unfavourable direction and the vertical stress corresponds to the overburden pressure. The mining method applied is sublevel stoping with preplaced cable bolting. Element methods have been utilized in the dimensioning of the crown pillar and the planning of preplaced cable bolting. A monitoring system has been installed to measure deformations and changes of stresses. Stopping has recently been started. Final feedback is expected in three years when the stopping area will have been exhausted.
Des methodes à elements F.E.M. et B.E.M. ont ete utilisees pour la planification d'abattage à la mine de nickel de Katalahti. La qualite de la masse rocheuse entre les niveaux +600 et +800 mètres varie de mauvaise à moyenne. La contrainte horizontale maximum est environ 50 MPa et en direction defavorable, et la contrainte verticale est de la même grandeur que celle du terrain de couverture. La methode d'exploitation employee est celle d'abattage par gradins avec boulonnage de cables pre-positionnes. Des methodes à elements ont ete utilises pour le dimensionnement des piliers en couronne et le boulonnage des cables. On a installe un système de contrôle pour mesurer les deformations et les changements de contrainte, et on v1ent de commencer l'abattage. On compte disposer des resultats definitifs dans trois ans lorsque la zone d'abattage sera defruitee.
Die Element Methoden (FEM und GEM) wurden zur Bearbeitung e1nes Abbauplanes fuer die Nickelgrube Kotalahti angewandt. Die Gebirge zwischen den +600- und +800-Sohlen sind von schwacher bis guter Qualitat. Die höchste Horizontalspannung in unguenstiger Richtung liegt bei etwa 50 MPa. Die Vertikalspannung ist gleich mit dem Deckgebirgsdruck. Als Abbaumethode wurde der Weitungsbau mit voreingezogener Kabelankerung angewandt. Die Element-Methoden wurden bei der Dimensionierung des Firstenpfeilers und bei der Planung der voreingezogenen Kabelankerung ausgenuetzt. Zur Messung von Deformationen und Spannungsanderungen wurde ein Überwachungssystem installiert. Mit dem Abbau wurde vor kurzem begonnen. Endgueltige Resultate sind nach erfolgtem Abbau des Gebietes innerhalb von drei Jahren zu erwarten.
Numerical methods, mostly the finite element method, have been occasionally used in the Finnish mining industry for ten years. A two and a half years project for applying element calculation technology to practical mine planning was started on the initiation of the Finnish mining industry in June 1980. The project has been carried out in close cooperation between the Finnish mining industry and different state research institutes. The total budget was 300'000 US$ of which one half was financed by the Ministry for Commerce and industry and the rest by the mining industry. The practical problems of the Rautuvaara iron mine of Rautaruukki Oy and the Kotalahti nickel mine of Outokumpu Oy formed the base material for this project. At present the Kotelahti mine extends down to a depth of 600 m. Annual production has been about 500'000 tons of ore. The Huuhtijarvi orebody is the largest one of the five orebodies. The ore is stoped mainly by sublevel stopping. Stopping between levels +600 end +800 has been planned during the project. This paper describes how element calculations have been applied to the stopping plan of the Huuhtijarvi orebody of Kotalahti mine. The determination of input data for element calculations is described too.
The Kotalahti mine is situated in central Finland. The area is built up by gneisses, schists and plutonic rocks, metamorphosed under the conditions of high grade metamorphism. Five deformation phases, including polyphase folding, intrusion tectonics and shear tectonics, have been distinguished by structural analysis (Gaal: 1980). The host rock of the Kotalahti nickel are is an ultramafic - mafic intrusion. It is located in a brachysynform structure close to a granite gneiss dome. The ore is built up by five orebodies. One of them, the Huuhtijarvi orebody, is the project test area. The Huuhtijarvi orebody is a pipelike formation (fig.1) dipping 80° NNW and reaching at least to the depth of one km. It has intruded along a subvertical fold axis and in horizontal section it forms a lens-like body (fig.2). Surrounding rocks are mica gneisses and amphibolites.
The rocks of the Kotalahti area are under high horizontal compression. The direction of the major horizontal stress σH1 is usually N-NNW and intensity some 50 MPa. σH2 is 25 MPa and vertical stress corresponds to the overburden pressure. At Huuhtijarvi, +800 level, the stress field has turned some 50° clockwise.
In Huuhtijarvi the following joint maximums with steep dips are found: WNW and NE(the directions of the fold limbs), NNW (the direction of the axial plane). In addition there exists a subhorizontal maximum and some random jointing.
