Ornamental stones are quarried both by means of open pit exploitations and by underground openings. This second case, even though limited, at this moment, to some geographical areas (e.g. Italy, Portugal, Croatia, France) and to some particular rock types (marble, hard limestone, conglomerates, slate) is increasing of importance both because of the improvement in cutting and sawing techniques, also for hard rock, and because of the increase in demand for materials. In particular, in mountainous areas or in rock bodies covered by thick overburden, the underground choice is necessary. The main features that characterize this field of geo-engineering are: the relative good quality of the rock masses; the relevant dimensions of the voids; the requirements for long term stability; the necessity of limited artificial support; the need for suitable design methods and for a link with the monitoring of the structures. The keypoints for the choice of the design procedures and for the monitoring are furnished in this paper on the basis of experience and learnings of different case histories.
The structure in underground ornamental stones quarries concerns good quality rock masses. In most cases, underground excavations are in fact supported by natural structures (pillars or barrier pillars), obviously when more than one void is present (e.g. the Carrara marble basin). In some particular cases, single openings are considered as caverns, because of their shape, generally due to the geological structure (e.g. the Candoglia quarry which supplies the Milan Cathedral). In these last situations attention is focused on the sidewalls and on the crown of the cavern, taking into account the fact that the dimensions can be relevant (e.g. about 21 m of width, 48 m of height and more than 80 m of length in the Candoglia quarry).
