The main purposes of the systematic measurement of convergence in the Germunde coal mine, were the direct monitoring of underground excavations stability and the definition of a rational criterion for the support design. It was required to treat the raw data obtained underground during several years, and to aggregate information regarding other essential factors for the excavation stability. Those were the density of support, as it was really present underground, and the geo-mechanical properties of the surrounding rock mass. The support design criterion was established concerning safety and cost minimization requests.
Les buts essentiels des lectures des convergences dans le mine de charbon de Germunde, etaient l'accompagnement direct de l'evolution de la stabilite des excavations et l'obtention des critères raisonnables de calcul du soutènment. Pour cet objectif, c'etait necessaire de compiler et d'interpreter des donnes des convergences obtenus pendant des annees et les completer avec d'autres facteurs influents dans la stabilite des excavations, soient la densite du soutènement installe dans les proximites des stations, les lectures des convergences et la qualite geomecanique du massif rocheux en place. Les critères de calcul du soutènement obtenus ont permit de maintenir les niveaux de securite et une redution des coûts d'installation et d'entretien.
Die Hauptziele Systematischer Konvergenzmessungen in der Kohlenbergbau von Germunde (Portugal) waren die direkte Verlaufskontrollen der Stabilitat unterirdischer Hohlraume sowie die Festsetzung vernunftiger Kriterien zu einrichten ihrer Abstuetzungen. Es war notwendig die untertagige Rohdaten - die uber mehere Jahre hinweg gesammelt wurden - zu verarbeiten. Darueberhinaus aber noch andere Daten uber Hohlraumstabilitat wie die Dichtigkeit der anwesenden Abstuetzungen und die gebirgsmekanichen Eigenschaften des Gesteinsmassives wurden beruecksichtigt. Die Auswahl der Abstuetzungkriterien erfolgete unter den Aspekten der Arbeitssicherheit und der Kostenminimierung.
The Germunde anthracite mine in northern Portugal, is about 25 miles from Oporto, and belongs to the Douro Coalfield. There are three vertical shafts and nine exploration levels at a maximum depth of 480 meters. The mining method utilized is a variant of the sublevel caving.
The maintenance of the applied supports demanded large amounts of almost irrecoverable timber and about 37% of the manual work used in the whole mine. A progressive replacement of timber supports by other more resistant was necessary in order to decrease costs and ensure safety, which is always the most important aspect in any mining enterprise. The metallic supports tested were mainly TH profile steel arches with friction couplings. Regarding the heterogeneity and complexity of the rock mass, five geo-mechanical situations surrounding the mining works can be defined (Table 1).
Since the determination of the prevailing stress field in the Germunde rock mass is extremely difficult, the geo-mechanical behaviour should be evaluated through quantification of the resulting effects in the excavations. Thus the convergence measurements are very important for estimating the stress field evolution. The convergence measurements are collected in three chords AB, AC and BC, disposed as practically equilateral triangles in the monitored sections - convergence measurement sites (see Figure 1). The technique selected for these observations is based in the setting of three pins, one vertically at the roof, and two horizontally located about 1m from the floor, giving the possibility for monitoring displacements in three directions, thus evaluating the influence of stress in various positions of space. The points A, Band C of the convergence measurement sites are materialized by metallic pins attached in long timber sticks which are thrusted in the ground, and by similar pins connected in the internal faces of the steel arches.
