The importance of soil mechanics in the risk assessment of temporary storage deposits of crushed aggregate

Due to the potentially high risk for the employees who are involved in the management of temporary storage deposits of rock aggregate materials, which are typically generated in quarries from the crushing operations of larger boulders, appropriate stability analyses need to be carried out, on the basis of the results of experimental campaigns that allow the coupled hydro-mechanical behaviour of the aggregate to be characterised for the site-specific meteorological conditions. The present paper describes the technical investigations, the laboratory activities, and the numerical analyses aimed at clarifying the causes underlying a slope instability that occurred within a stockpile of a silica sandy gravel, which resulted to be fatal for the operator behind the wheel of the loader that was removing the aggregate from the base of the stockpile. Once the contribution of the partially saturated conditions to the shear strength of the aggregate had been determined, and the most likely geometrical layout of the stockpile at the moment immediately preceding the accident had been identified through the processing of both terrestrial land surveys and satellite imagery, the triggering of the aforementioned instability phenomenon was studied by means of three-dimensional finite element analyses. The use of a specialised numerical software, specifically developed to model debris flows and rock avalanches, allowed the dynamics of the consequent landslide to be simulated, with the final goal of verifying the conclusions previously drawn from the results of the finite element stability analyses.