The Prevention through Design approach as a key tool in tunnelling operations and muck reuse

Purpose: on the basis of some case histories the problems are here discussed which can arise where a not exhaustive preliminary risk assessment is available, based on a quite detailed knowledge of the characteristics of the material to be excavated. Such problems cover occupational risks deriving from uncorrected selection of the tunnel driving technique and fittings layout, and environmental criticalities associated to unfeasible muck management and destination. The target of the present research work developed with reference to the tunneling operations, is to discuss an effective approach to the safety and health protection of the workers at the construction site, and to the environmental quality conditions in the surrounding areas. The latter should be referred to both the environmental protection, and to the reduction to a minimum of the environmental impact, this involving in particular the possibilities of reuse of the materials resulting from the tunnel driving operations. Methods: the research work is a part of a wide range study carried out by the Department of Environment, Land and Infrastructures Engineering (DIATI) of the Politecnico di Torino for the evaluation of the possibilities of the muck reuse. Nevertheless, this approach is possible only in the case of granted absence of hazards due to the presence in the rock mass to be excavated of noxious materials such asbestos, crystalline silica, etc., since, taken into account that in particular in the case of carcinogens, corrective action following exposure or dispersion is not acceptable, the presence of critical pollutants requires both special preventive actions for the workers health, and the impossibility of any reuse of the muck which could introduce risks for the users (e.g. during mechanical processing involving feeding, crushing, milling, sizing and sorting operations, etc.). Results: the first result is a discussion on the possibilities and techniques of a predictive assessment of the asbestos content in the rock, with special reference to the reliability of the achievable results. The second result is a discussion on the technical possibilities available to minimize the occupational risk where critical rock formations must be excavated. Finally, some considerations are provided on the often underestimated problem of the safety fittings availability, which can prove quite dramatic in the aforesaid critical situations. Conclusions: even if for both economic and environmental reasons the management of the material resulting from tunnel driving operations should be carefully evaluated, and any possible reuse considered, the very first step of such an analysis should be a very careful investigation on the possible content of critical minerals in the rocks to be excavated. In the case, no reuse is possible and a selection of the tunneling techniques and technologies suitable to the minimization of the occupational and environmental risks becomes of primary importance.