ABSTRACT:

The reinforcement of large underground mining cavities is more and more realised with the help of cable boiling. Geotechnical investigations and research of appropriate modelling methods have been carried out in two european mines, using cable bolting, in order to improve the understanding of its action and to optimise its parameters. The first example is Sotiel Mine(Almagrera S.A., Spain) which is mining a polymetalic orebody in fractured hard rock, with cut-and-fill method. The second example is Brusada mine (Unitalc, Italy) which exploits a soft rock deposit (talc) by long hole open stoping method. Global models suitable for discontinuous medium as well as local models (taking into account parts of cables) have been elaborated and used for simulate the role of bolts and their interactions with the rock mass. The results give guidelines for the miners' choices.

RESUME:

Le renforcement des excavations minières de grandes dimensions fait de plus en plus frequemment appel au boulonnage par cables. Deux exploitations europeennes utilisant ce type de renforcement onl fait l'objet d'investigations geotechniques et d'une recherche de methodes de modelisation avec pour objectifs de mieux en comprendre le mode de fonctionnement et d'en optimiserles paramètres. Le premier exemple est celui de la mine de Sotiel (Almagrera SA, Espagne) qui exploite un gisement polymetallique de roche dure fracturee par tranches montanles remblayees. Le deuxieme exemple est celui de la mine de talc de Brusada (Unitalc. Italie) qui exploite par grandes chambres vides un gisement en contexte de roche tendre. Des modèles globaux adaptes aux milieux discontinus et des modelisations locales ont ete elabores et mis en oeuvre pour rendre compte du rôle du boulonnage et des interactions avec Ie massif rocheux. Les resultats permettent de guider I'exploitant dans ses choix.

ZUZAMMENFASSUNG:

Große unlererdische Hohlraßme werden immer hauefiger mil Seilankem unterstuetzr. In zwei europaischen Bergwecken, die diesen Ausbautyp massifeinsetzen, wurdenausfuehrliche geotechnische Untersuchungen und numerische Modellberechnungen Durchgefuehrt, mit dem Zweck, die Arbeitsweise dieses Ausbautyps naher zu characterisen und seine Parameter zu optimieren. Das erstebeschribene Beispiel ist das Erz-BergwerkSotiel (Almagrera A.G., Spanien). Das zweite Beispiel ist ein Kalk-Brergwerk in Brusada (Unitalc, Italien).

1. INTRODUCTION

In this paper are presented the results of numerical modelling based on geotechnical investigations carried out during mining in experimental stopes of two different underground mines, to provide a better understanding of the mechanical behaviour of fractured rock masses. The first mine, named Sotiel mine, is located near the village of Calañas in Andalusia, the southern province of Spain. The Almagrera S.A. company exploits a polymetallic sulp hide deposit, 950 m long, 50m wide, at adepth between 300 m to 650 m below ground surface. The orebody has a general strike oriented East-West and a dip of 45° to North. The hostrocks mostly consist of volcano-sedimentary rocks such as cinerites, tuffs and schists, A few years ago, the mining method of cut and fill leaving post-pillars was used. In this case, the rooms were distributed in two levels, 75 to 80 m high, separated by a crown pillar of 20 m thickness. In each level, the rooms were separated by barrier pillars of 36 m width. The typical mining slope is delimited by four post-pillars 8 m high, 5 m × 8,3 m, separated one another by about 11 m (figure I). These post-pillars assure the local stability of the stope roof by preventing the fall of very large blocks, due to the natural fracturing of the mineralised zone. A serious accident in 1985 led the company to use a further and systematic roof support by fully grouted cable-bolts distributed on a regular grid. In accordance with the results of the geotechnical studies, it is assumed that the roof of the stopes behaves as an assembling of rigid blocks bounded by major planes of natural discontinuities. The second exploitation, called Brusada mine, is located near the village of' Lanzada (Sondrio province) in the central Italian Alps, where the Unitalc company exploits a talc deposit. The orebody is a vein of extremely variable width (3–45 m) with a general N060° strike and a dip of 70° to the North, whose hostrock consists of serpentinite.

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