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Estimation of natural asbestos content in rocks by fracture network modeling and petrographic characterization
برآورد محتوای آزبست طبیعی در سنگها با استفاده از مدل سازی شبکه شکستگی و خصوصیات پتروگرافی-2020 Asbestos may constitute a severe health risk when meta-ophiolites are excavated for large infrastructural projects.
For public acceptance, a reliable estimation of the content of Naturally Occurring Asbestos (NOA) is necessary
for the design of construction sites, workers safety and spoil management. In the framework of a research
project supporting the final design of a highway tunnel system in NW Italy, SEM-EDS (Scanning Electron
Microscopy – Energy-Dispersive Spectrometry) quantitative analyses were performed to provide a direct NOA
content estimation by counting and weighing the asbestos fibers in the rocks, after a chemical and geometrical
characterization. The direct NOA content estimation was compared with an indirect estimation obtained through
a fracture network modeling based on a structural survey on a selected outcrop and statistical analysis of a
relative digital image. The fracture intensity, inferred from the fracture network model, was multiplied by
coefficients deriving from the semi-quantitative estimation of the geological relations between asbestos mineral
occurrence and fracture size, thickness and distribution. A good agreement between the indirect NOA estimation
and the average result of the SEM-EDS analysis was obtained. Thus, the statistical analysis of the fracture network
may represent a valuable support to the SEM-EDS quantitative analysis based on mineral fibers counting.
However, the quality of the indirect NOA estimation depends on the postulates for inferring the coefficients
describing the distribution and occurrence of the asbestos minerals within the fractures. This Note discusses the
above-mentioned issues, as well as those concerning the procedure for a representative sampling of NOA-bearing
rocks and fractures. Keywords: Naturally occurring asbestos | Fracture network modeling | Meta-ophiolites | Geological hazard |
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