3D slope stability analysis of a limestone quarry expansion in Northern Italy

Slope stability is a crucial aspect in case in quarrying, both in term of legal and technical restrictions. The availability of data regarding the rock mass characterization is not sufficient to guarantee a satisfactory stability analysis, which must be assessed by means of more accurate procedures. Limit equilibrium analyses have been used since many decades, as they can give satisfactory results for simple cases, such as planar or wedge blocks. Nevertheless, when dealing with more complex cases, such as opencast quarries and mines, where the slope geometry consists on several benches plunging in different directions, this simplified approach cannot give a satisfactory answer. In this scenario, numerical models can return a much more complete and accurate assessment of the overall stability. The paper describes a possible approach to evaluate the stability of the slopes of a limestone opencast quarry in Northern Italy. The country is experiencing a growing demand of limestone for the production of cement for the construction sector and this determined the need to expand the previous exploitations. Since the quarry experienced several expansion plans throughout the years, several site investigation campaigns have been carried out and the results were not always consistent with each other. Starting from the two most recent rock mass characterizations and by using 3D numerical models, the overall stability has been simulated by means of continuum and discontinuum analyses, to obtain a reproduction of the real episodes of instabilities that occurred in the past. The implementation of models with reliable data is essential to obtain results that are comparable with the reality: this would allow to proceed more effectively and safely with the exploitation of the future slopes.