Abstract:

The Portoro "marble" is a fine variety of black limestone from the La Spe-zia area, in Liguria (North-western Italy), which consists of a Liassic limestone with limonite and calcite veins. The Portoro typically crops out close to the Portovenere village and Poets' Gulf area, which is very known and sensitive in terms of scenery and tourist appeal. Even if few stone quarries are still working, it is evident how quar-rying must be done with special care. So underground excavation is more and more developing, in order to control waste production, environmental impact and slope in-stability: big blocks are mined in large underground chambers whose roofs are sup-ported by pillars. In this study a numerical modeling, based on a distinct element method was used, in order to compare stresses and displacements with the in situ measurements and to reach an optimum quarrying design. This research mainly aimed at improving the working conditions, as regards different topics: work safety in under-ground environment; prevention of fracturing of intact rock, induced by excessive stress concentration; improvement of the extraction process, to quarry intact, bigger stone blocks and produce less waste material; providing the underground chambers with long-term stability conditions, for possible future use.

1 INTRODUCTION

This study deals with the underground quarrying of ornamental stone in the promontory of La Spezia, in Italy (Fig. 1). This area gives spectacular sights on the La Spezia Gulf, the Portovenere harbour and the Palmaria Isle, and on the Ligurian Sea. Several quarries have been active here since the 19th century, excavating stone materials for different uses, among which the ornamental and construction purposes have prevailed. At present very few of them are still active, for mining the Portoro ornamental stone, a Jurassic black stone with intense yellow and veins.

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