A stability analysis on the possibility of using room and pillar underground mining method, in a marble quarry in Alentejo (Portugal) with backfill, is presented. Given the data provided by the laboratory tests over marble samples and in situ tests as well as a thoroughly geology acknowledgment of the area, a new excavation design was presented for the underground phase, using Finite Element analysis, where global and local stability is assessed. Moreover, the innovative idea, for marble underground quarries, was to contribute to the circular economy and the current environmental policies by making a use of the quarry’s waste rock, as the principal aggregate for a backfill material, that not only reduces the impact of wastelands in the surface but also acts as support for the newly excavated area leading to residual pillars recovery. Given this, an overview of the stress displacement is presented, and the main potential instability zones are assessed. The results are a quantitative contribution to the characterization of the rock mass for alternative ways of ornamental marble production in this region.
The production of natural stone in the Portuguese region of Alentejo, specifically in the Ossa Morena Zone (ZOM), has been historically popular and profitable throughout centuries [1]. This region, and inherently, the mineral deposit, is one of the top marble producers in the world. Despite its high profitability marble is a non-renewable geological resource and following the European standards of circular economy [2] operations in the quarries have seen the need to develop more sustainable and greener solutions for the extractive methods that produces big volumes of wastes, as well as to recover the maximum mineral possible without jeopardizing the environment and safety of workers and equipments.
According to [3], technical and economic problems in the Alentejo marble quarries arises when changing the excavation method to underground mining. In this case, the underground openings are excavated directly in the productive and massive rocks, avoiding the removal of overburden. According to this study, it is necessary to maintain stable structures in the rock (rib pillars and eventually thick horizontal beams) without excessive loss in block recovery. A stability analysis is the key to understand how the model will react to the given conditions [4]. The application of tools and models in rock mechanics to underground exploitations is justified for safety reasons, guaranteeing the stability of the exploitation in relation to workers and, for economic reasons, by controlling ground deformation and excavation to prevent the disruption of the work [5]. For the room and pillar method, several works have studied the requirements of this mining type to ensure safety [6].