An inter-disciplinary geotechnical study has been carried out in an Austrian magnesite mine. The paper describes the how geological data, in situ and laboratory tests as well as subjective, empirical, geophysical and numerical methods have been used to identify critical areas in the mine.
In einem österreichischen Magnesit Bergbau wurde in den letzten Jahren eine interdisziplinare geotechnische Studie durchgefuehrt. Der Vortrag beschreibt den Einsatz subjektiver, empirischer, geophysikalischer und numerischer Methoden zur Identifikation geotechnischer Problembereiche Ces dernières annees des etudes geotechniques interdisciplinaires sont effectuees dans une mine souterraine de magnesite en Autriche. Ce rapport trace l'application des methodes subjectives, empiriques, geophysiques et numeriques pour identifier les zones problematiques dans la mine
The need for a methodology of geotechnical risk assessment of Austrian underground mines was formulated by the Austrian mining Inspectorate. The Veitsch Radex GmbH & Co as owner of one of the largest Austrian underground operations participated in the development of this procedure. The geotechnical investigations started in 2000.
(Figure in full paper)
The study mine is located in the eastern part of the Austrian Alps 150 km SW of Vienna. The sparry magnesite deposit is located in the Hackensteiner Formation of the Silurian/Devonian Laufnitzdorf Group which is a part of the Graz Paleozoic Thrust system (Fig. 1). The massive mineral body has a length of approximately 2 km, and a width of 150 m to 500 m. The thickness varies between 50m and 200 m. The general angle of dip of the deposit is ~ 25° to the south and opposite to that of the mountain slope. The overburden varies between 0 m up to 1,000 m. The tectonic regime is dominated by two steep fault systems trending in ENE-WSW, and NNE-SSE directions. These systems displaced parts of the mineral body for distances of a few meters only. Host rocks of the magnesite are anchimetamorphic slates rich in organic material, siltstones, sandstones, lydites, limestones and metatuffs of poor to very poor mechanical properties. Mining activities started at the beginning of the last century, and a remaining lifetime of 20–30 years is estimated. The mining method is post pillar mining using uncemented backfill. The pillars are rectangular in cross-section with a width of ~5 m and a length of ~15 m. In a first step a 7 m high opening at the deepest point of a mining area is excavated. Afterwards backfill is placed to a height of 3.5 m. The backfill is used as a working level for the next 3.5 m mining slice. Depending on the geometry of the deposit up to 26 slices have been mined resulting in pillar heights ranging from 7m to more than 90 m.
(Figure in full paper)
In the first step a full 3D computer model of all excavations was created, Figure 2. All available geological information, drill core data, geometry of the deposit, geostatistical block model etc. were added to this model.