Stability analysis of fractured rock mass excavation in ornamental stone quarries by mean of 3D numerical modelling

The activities for the exploitation in the Carrara marble basin have generated and continue to create excavation walls and permanent underground openings of unusual shape and dimension. The tendency to enlarge the excavation is due to the high production needs of the mining companies and is favoured by the extreme mechanization of the mining activity. In this context it is necessary to find a reliable design and evaluation criteria to describe the static behaviour of the post excavation rock structures. This study is therefore aimed the analyses of the state of stress and strain induced by the excavation of large underground openings in fractured rock masses, where ornamental stones exploitation is carried on. The study illustrates the interpretation and modelling of a case of instability in which, due to the excavation operations, a volume of around 55000 m3 of Carrara marble detached from the mountainside and fell, obstructing the entrance of the underground exploitation site. This paper, after a brief theoretical review, follows the evolution of the disturbed zone by performing parametrical analysis of some fundamental features such as joint cohesion, joint friction coefficient and in-situ state of stress in order to back analyse and understand the occurred instability phenomena. Copyright 2006, ARMA, American Rock Mechanics Association.