The Petralia salt mine in Sicily was the subject of rock mechanics studies in order to characterize the rock mass and to analyse the stability conditions in the mine. Tests were carried out both in the laboratory and in situ, and at the same time the static performance of a section of the mine that was going to be excavated was monitored. In this way the design parameters were estimated. The assessment of the static conditions in the mine was carried out in two phases: first, the pillar strength and of the likely safety factors was assessed; then, numerical modelling based on the Displacement Discontinuity Method was used. Stress distribution in the mine structures was worked out with reference to the present and future mine layouts. Thus it was possible to decide to improve the extraction ratio by thinning down the pillars.
Le travail concerne les etudes de la mechanique de roches effectues à la mine de sel de Petralia en Sicile, afin de caracteriser la masse des roches et d"en analyser la stabilitè. Des essais de laboratoire et des mesures de deformation autour des cavites et dans les pilliers, pendant l"excavation d"une section representative de la mine, ont ete effectuees. Le but principal etait d"obtenir les paramètres de la masse. Après l"evaluation des contraintes dans les piliiers et du facteur de sûrete des modeles mathematiques bases sur le Displacement Discontinuity Method (Modele elastique paratridimensional) ont ete etudies. La distribution des contraintes dans les structures de la mine a ete evaluee en relation aux plans des developpements actuels et futurs; cela a permis une evaluation soignee des conditions de stabilite des structures de la mine.
Die zur Beschreibung der gebirgsmechanischen Situation in der Petralia Salzmine (Sizilien) durchgefuehrten Studlen umfaβten Arbeiten zur gesteinscharakterisierung und Stabilitatsueberpruefung. Laboruntersuchungen und in situ Versuche erfolgten In engem Zusamnenhang mit der Meβwerterfassung In enema im Abbaub befindlichen reprasentativen Grubenteils. Die Hauptzielsetzung dabei war es, die Auslegungsparameter fuer die untertagigen Grubenbaue zu beatimmen. Zur Einschatzung der Pfeilerkrafte und der notwendlgen Sicherheitsfaktoren, wurden numerische Modelle basierend auf der DDM-Methode (dreidimensionaler elastischer Modellansatz) angewandt. Die Spannungsverteilung im Grubengebaude wurde sowohl im Hinblick auf die derzeitige als such auf die zukuenftige Grubenauslegung berechnet. So war eine sorgfaltige Einschatzung der Stabilitat des Grubengebaudes möglich.
The Petralia salt mine is situated at 800 m above mean sea level in the Madonie, in the north - central part of Sicily. The salt deposit with an overburden of 100 m extends downwards for 200 m approximately. The mine has been worked since 1972 by Italkali S.p.A.. It is being mined by the room and pillar method, on multiple levels (Figure 1). It produces both "industrial" salt (700,000 ton per year approximately) and "edible" salt (200,000 ton per year approximately). Initially the conventional blasting method was used, to a depth of 120 m below the roof of the salt deposit. Later on road-headers have also been used, with typical mining techniques as shown in Figure 2. In 1990 the problem of increasing the extraction ratio (60% approximately) was raised. A rock mechanics programme was therefore carried out with the main aim of assessing the stability conditions of the mine structures.
In the levels that have been most recently mined the extraction ratio is fairly constant in the various zones, even though the resulting geometry (in particular the shape of the pillars) is not very regular: pillars of roughly a square shape, of about 25 m on each side, are flanked by pillars that are of a rectangular section of 15 × 40 m.
