ABSTRACT:

The aim of this investigation was to select the most adequate type of support, with a consequent increase in safety and reduction of maintenance costs. Underground geological mapping was complemented with the measurement of fracture density, so that a geo-mechanical classification of the rock mass could be developed, in order to establish the selection of support systems. Mechanical tests were conducted in samples collected from boreholes for the most common types of rocks (coal, shales, sandstones and conglomerates). Supplementary information was achieved by convergence measurements, load cells and extensometers. The application of this method allowed to predict the necessity of different support systems in the deepest level of the mine.

RESUMÉ:

Cette recherche envisageait, prioritairement, le choix des types de soutènement, les plus convenables, en assurant l'acroissement de la securite et la reduction des coûts d'installation et d'entretien. La cartographie geologique en mine a ete completee par des mesures de la densite des fractures, dont le but etait d"etablire une classification du massif rocheux et d'aboutire à une critère de selection du soutènement. Des essais mecaniques ont ete efectues sur echantillonage des roches les plus communes en mine (charbon, schistes, gres, conglomerats). Les mesures de l'appareillage geomecanique ont fournit des renseignements supplementaires. La methode utilisee a permi la prevision des differents types de soutènement a apliquer, cas a cas, dans les nouveaux travaux miniers.

KURZFASSUNG:

Das Ziel dieser Untersuchung war eine mehr anpassende Abstuetzung der Kohlenergbau von Germunde (Portugal) herauszufinden, und dabei nicht nur die Arbeitssichereit erhöhn, zu konnen, aber auch die laufenden Abbaukosten zu verringen. Damit eine gerbirgsn mechanische Klassifikation des Gesteinsmassives und die anpassenden Abstuetzungen entwi- ckelt werden konnten, die untertagige geologische Kartierung wurde durch intensiven Verwerfunsebenmessungen erganzt. Mechanische Pruefverfahren fuer Bohrenkernproben aus Khole und haufigsten Gesteinsarten (Schiefer, Sandsteine und Konglomerate) wurden durchgefuehrt. Zusatliche Angaben wurden durch Konvergenzmessungen, Druckmessdosen sowie Dehnungsmesser erzielt. Die Anwendung dieser Methoden erlaubt wir, fuer den tiefsten Grubenhorizonten die anpassenden Abstuetzungen voraussehen zu konnen.

1 INTRODUCTION:

The geo-mechanical behaviour of Carboniferous lithologies and of the surrounding rock mass, frequently incompetent and with a very high deformability, always led to supplementary, frequent and expensive maintenance works in the Germunde coal mine. The main problems related to the geo-mechanical conditions of the underground excavations are: - To ensure safety, through a perfect knowledge of the occurrying phenomena. - Gradual elimination of timber supports by using more effective and cheaper support systems. In underground mines, it is important to know the characteristics of rock mass discontinuities, before the planning and the execution of excavations, in order to ensure the stability in the most economic and safe way. Therefore, every structural feature that, for its nature, could interfere with the stability of the mine openings should be determined. The lack of this type of studies related to underground mine operations can eventually give rise to unpleasant surprises, such as an increase in the support and stabilization costs, production delays or even loss of human lives.

2 GEOLOGICAL SETTING:

The Germunde coal mine belongs to the Douro coalfield, which forms a narrow strip of continental Carboniferous formations striking NW-SE, extending for approximately 50km (Figure 1). In the Germunde area, the footwall of the Carboniferous formation is formed by upper Precambrian to lower Cambrian argillaceous schists and greywackes. The hanging wall, on the northeastern side of the trough, is formed by Ordovician slates and quartzites, integrating the southwestern limb of the Valongo anticline. The contact between the Carboniferous and the Ordovician formations is a thrust fault, filled with an important amount of clay which in part controls the infiltration of water into the mine.

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