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The presence of naturally occurring asbestos (NOA) in many areas worldwide requires an enhanced geological risk evaluation to ensure workplace safety from asbestos during large construction projects. Due to the complexity of the geological risk definition, health and safety regulations for working with asbestos-bearing materials are often not enforceable in NOA settings. Therefore, to correctly estimate the risk of NOA in these scenarios, new procedures are urgently needed to provide (1) a detailed geological model representative of the possible presence of the asbestos, (2) representative sampling, and (3) a reliable quantitative determination of asbestos content in rocks. This work aims to discuss the improvements on the two latter points specifically developed during the design of the "Gronda di Genova" project, a 50-km-long tunnel bypass partially designed in the NOA-bearing meta-ophiolites of the Ligurian Alps and ophiolites of the northern Apennines in Italy. Implementation of Gy's theory on sampling was used to maintain statistical validity during sample processing from the primary sample to the analytical sample and is here described. The scanning electron microscopy/energy dispersive spectroscopy procedure for the quantification of NOA was improved with an error analysis delivering the minimum number of fibers to be measured to achieve the best analytical results. [ABSTRACT FROM AUTHOR]

For a reliable evaluation of the geo-environmental risk due to naturally occurring asbestos (NOA) during rock excavation of large infrastructure projects, a proper procedure is needed. First, it is necessary to provide a detailed geological model tailored to the NOArelated issues that should drive the rock sampling procedures in order to obtain a representative sampling. The sampling procedures should take into account lithological variability and relative spatial distributions of the rock units. The geological model for NOA should be thus constrained by the main NOA petrofacies occurring in a given geotectonic context, which take into consideration both the mineralogical and structural features, and the identification of NOA homogeneous zones in which the NOA petrofacies are distributed. In this paper, some geo-environmental problems faced during the excavation, in meta-ophiolites, of a long highway tunnel are described. The geological model of the complex setting of the tunnel area (northern Italy, Alps-Apennines junction) is described, focusing on how the NOA-related problems were addressed to allow reliable and detailed estimations of NOA contents for each NOA homogeneous zone and the relevant tunnel layout segment. [ABSTRACT FROM AUTHOR]

Realization of large geo-engineering projects in rocks containing naturally occurring asbestos (NOA) must address several crucial geo-environmental issues, including the design of the construction site, the enforcement of health protection measures and the environmentally responsible spoil management. This leads to a compelling need to develop effective and standard procedures to evaluate the distribution and concentration of NOA in rock volumes. NOA petrofacies are here proposed as an innovative tool to evaluate the asbestos distribution and concentration in complex geological settings. NOA petrofacies are fundamental asbestos-bearing rock types, consisting in recurrent lithological and structural features controlling asbestos occurrence. Here we describe and discuss how the NOA petrofacies approach was utilized in a geo-environmental study for the evaluation of asbestos content in a complex meta-ophiolite suite, which will be crossed by the "Gronda di Genova" highway by-pass project (Genoa, NW Italy). NOA petrofacies were used to predict the distribution and relative abundance of NOA in geologically homogeneous zones characterized by the occurrence of specific NOA minerals. [ABSTRACT FROM AUTHOR]

In the southern Dora-Maira Massif, Western Alps, slivers of continental crust with similar lithologies, but recrystallized during the Alpine orogeny at different peak-Pconditions, are exposed. They include the Brossasco-Isasca Unit (BIU) where coesite was first discovered in continental crust. A new 1:20,000-scale geologic map and related cross-sections of the whole BIU and adjoining units is presented, in which the most significant features useful to infer the pre-Alpine history and the Alpine tectonic and metamorphic evolution, are summarized. Thanks to detailed petrography and petrology, the geologic map shows the precise location of ultra-high pressure (UHP) minerals (such as coesite), and the locations of the most significant mineral assemblages (such as kyanite + jadeite). This innovative approach is used to distinguish the BIU from the adjacent units. Relict pre-Alpine structures (such as igneous intrusive contacts with basement xenoliths and metagranitoids) are summarized in a sketch illustrating the geologic setting of the UHPmetamorphic unit as inferred before the Alpine orogeny. [ABSTRACT FROM AUTHOR]

For a reliable evaluation of the geo-environmental risk related to the presence of naturally occurring asbestos (NOA) in rocks excavated for large infrastructural projects, a proper procedure has to be followed. First it is necessary to provide a detailed geological model, tailored on NOA-related issues, to allow planning a proper strategy for representative sampling. Sampling should meet two criteria: the lithological and the statistical representativeness.The geological model for NOA should be thus constrained by the main "NOA-related petrofacies" -i.e., classes of rocks which share common lithological, structural and NOA content features- occurring in a given geotectonic context, and the identification of "homogeneous zones" into which the NOA petrofacies are subdivided. Here we describe the approach followed for the evaluation of the asbestos content in the excavation, in meta-ophiolite rocks, of a complex highway tunnel system in NW Italy ("Gronda di Genova" project). The geological model of the complex setting of the area (Alps-Apennines junction) is described focusing on how the NOA-related problems have been addressed to allow reliable and detailed estimations of NOA contents for each homogeneous zone and the relevant tunnel layout segment. [ABSTRACT FROM AUTHOR]

Abstract: Multiple deformation mode switches from shortening to extension have been detected in the Penninic units of the Urtier Valley, to the north of the Gran Paradiso massif. An early shortening phase, whose traces are poorly preserved, led to the tectonic burial of rock units to high pressure conditions. Subsequent extensional shearing (SZgr 1) led to the formation of mylonitic fabrics. During this event the eclogitic Piemonte unit was exhumed to greenschist facies conditions (P =0.2–0.3GPa) in the footwall of the blueschist Piemonte unit. Exotic slices of continental basement and Mesozoic continental shelf carbonates are found along their contact, implying the existence of older thrust stacks dissected by the younger extensional shear zones. The extensional structures were later affected by upright folding (Fu), indicating yet another deformation mode switch, which led to re-burial to P =0.6–0.8GPa. Later multi-stage deformation culminated in an episode of extensional shearing with top-to-the-west kinematics (SZgr 2). Therefore, at least two shortening–extension cycles affected the Piemonte units of the Urtier Valley. Existing geochronological data allow less than 20Myr for the complex deformation history discussed here. Shortening–extension cycles can be inferred also from published studies from other sections of the Western Alps. However, while the first shortening–extension cycle was widespread in the Penninic units, the lateral extent and relative timing of the second cycle in different areas are still unclear. [Copyright &y& Elsevier]