Marble exploitation in the Apuane Alps gives rise to rock wall faces and underground voids of uncommon size and shape. The trend towards gigantism in quarry operations (the height of the faces increases up to 150m, the length of underground voids to 80-120m, their height to 30-50m and their span to 20-40m) is sustained by the higher outputs required and favored by the growing mechanization of the stopes.
It is known however that ornamental stones exploitation, both surface and underground, is strongly affected by the rock mass jointing and by the stress state in natural supporting structures (e.g. walls, pillars). Indeed, joints intersecting excavations can give rise to free monoliths, and the design of the excavations must account for that dangerous event, in all cases, but especially in the design of the natural supporting structures to warrant safety against collapses). And the safety requirement must be satisfied without impediment of the yield of commercial blocks. Similarly the state of the stress of the rock due to the natural conditions and to the changes induced by the xcavation must be known, and the works planned in such a way that stress concentrations, loading to rock burst and collapses are avoided. It seems obvious, in that matter, the need of reliable and rigorous design and evaluation criteria, resting on rock stability experimental research, but in fact, the design of surface and underground quarries is still supported by operators experience and by empirical rules lacking sound scientific background, not by geomechanical ground control. What is strongly needed is the continuous survey of the rock stress changes during excavation, which represents the basis of the observational method typically adopted in geotechnical studies, of which examples abund in large civil works excavations and in tunnelling.
Though being such an essential body of knowledges and controls, which should represents the basis for rational analysis, still a remote objective, a technical research program launched by Regione Toscana through his Departments (U.S.L. 1, 2 e 12 i.e.: of Massa e Carrara "Mining Engineering Unit", of Lucca - Serchio valley "Accident prevention and health at workplaces" and of Versilia "Accident prevention and health at workplaces") along with CNR-IGAG and CNR-IGG Institutes and Parma University represents a good starting point. The program consists in an experimental and analytical evaluation of the present quarry state. The title of the research is "analysis of the state of stress" and the aim is to collect reliable data on the local stress in rock faces, pillars, walls, and so on in selected quarries and to compute and improve by comparison of the experimental data with estimated values issuing from numerical computations, the information on the statical behaviour of the marble quarries, thus improving the safety against rock falls and collapses in quarry exploitations.
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