The importance of natural fractures in ornamental rock quarries is manifold as they control the size and quality of blocks to be extracted, as well as the extraction methods, equipment types and the overall economics of production. It is obvious that realiable characterizations of the tridimensional pattern of fractures are essential for quarry exploitation planning, to be performed as soon as possible within the time schedule of any ornamental rock undertaking. Use of scan-line surveys, which are already routine in tunneling and underground mining, has proved to be very useful for marble quarrying, as it is shown by means of two examples described in the paper


L'importance des fractures naturelles dans l'exploitation des carrières de roche ornementale est multiple car elles contrôlent la taille et la qualite des blocs qui sont obtenus, et aussi les methodes d'extraction, les types d'equipment mecanique et l'economie de la production. II est evident que des caracteristiques fiables des reseaux de fractures dans les massifs rocheux sont essentielles à la planification de l'exploitation des carrières, et devront être realises dès que possible dans Ie programme de developpement de ces projects. L'utilisation des lignes d'echantillonnages, qui se pratique habituellement dans les tunnels et les mines, semble avoir beau coup d'avantages pour l'optimisation des carrières de marbres, comme il est demontre par les deux exemples ci-joints.


Die Bedeutung natuerlicher Kluefte in Steinbruechen fuer Verzierungsgesteine ist mannigfaltig, da sie die Grösse und Qualitat der zu gewinnenden Blöcke kontrollieren, sowie auch die Abbaumethoden, die Geratetypen und die allgemeine Produktionswirtschaftlichkeit. Es ist einleuchtend, dass vertrauenswuerdige Kennzeichnungen des tridimensionalen Kluftmusters fuer die Steinbruchsabbauplanung wesentlich sind, und so frueh wie im Zeitplan irgendeines Verzierungsgesteinunternehmens möglich ausgefuehrt werden sollen. Der Gebrauch von Erkundungslinievermessungen, die im Tunnelbau und Untertagebergbau schon Routine sind, hat sich fuer den Marmorsteinbruchabbau als sehr nuetzllch erwiesen, wie mittels zweier, im Referat beschriebener Beispiele gezeigt wird.


All rock masses contain discontinuities of various sizes and attitudes which control their mechanical behaviour, either by increasing their deformability and water conductivity or by reducing their strength. Appropriate knowledge of the geometry and properties of discontinuities within any rock mass is essential for the design of engineering works which are to be done inside, or above, or even with materials extracted from rock masses. Production of dimension stones from quarrying is one of technical areas where accurate insight on the presence of fractures is fundamental to establish planning strategies for rock exploitation, as well as analysing the economic recovery of the extracted volumes, so that excessive amounts of waste and broken rock are avoided. The fact that most geologic deposits where ornamental rocks are found, contain large quantities of joints and other discontinuities has led to the failure of many endeavours for the industrial exploitation of that resource, which has a commercial value that depends on the size of blocks, their uniformity of properties, absence of deffects and, last but not least, their aesthetics. One common drawback of dimension stone quarrying consists of expending time and money to extract rock volumes that in the end show many fractures, when the correct decision should have been to avoid their removal, if previous surveys indicated that heavy fractured condition. Furthermore, correct quarry planning must define "a priori" directions for cutting primary blocks, in order to eliminate additional fracturing caused by the extraction procedures. The seriousness of this problem is justified by the great quantities of small blocks removed from dimension stone quarries, which represents on the average, between 60% and 90% of all extracted volumes.

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