Geotechnical Risks in Natural Stone Quarries

Abstract

After the landslide of a quarry slope which caused the collapse of the road between Borba and Vila Viçosa, it became imperative to increase surveillance and slope stability studies in quarries in Portugal, and particularly the Estremoz Anticline. Over the years, as exploitation gets deeper, the most superficial areas of the slopes are inadvertently neglected, gradually becoming more unstable, for morphological reasons of the surface, due to inappropriate human intervention and weathering of the rock mass. This paper reflects several studies carried out to understand the main causes and factors that influence quarries’ slope stability. The methodology comprises analysis of different lithologies and contacts between geological formations, measurement of discontinuities and their geometry in relation to the free faces of the slopes. The results of the study indicate two types of failure causes in the several exploitation cavities, which compromise the integrity of the slopes with different degrees of hazard. In conclusion, although the potential risk of failure of quarry slopes is mainly due to the weathering and geological structure of the rock masses, these geotechnical risks are increased by the excessive height and verticality of these slopes, with exploitation techniques and mining planning measures, sometimes not very prudent in terms of the safety of workers and property. This study led to the conclusion that many situations of slope instability risk in this area of marble quarries could be resolved if the perimeters of the cuts were widened by joining adjacent cavities, developing integrated exploitation.