Utveckling av expertsystem för bedömning av bergmaterialens mekaniska egenskaper: komplement till VTI rapport 715

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Eva Johansson
Karel Miskovsky
Magnus Bergknut

On behalf of the Swedish Transport Administration, Luleå University of Technology (LTU)/Envix North Ltd and the Swedish National Road and Transport Research Institute (VTI) developed the expert system for evaluation of rock materials' mechanical properties, i.e. an evaluation system based on petrographic parameters. The project aimed to provide a prompt documented evaluation of rock mass quality and its practical use as aggregate, even when rock is covered by drift material. The project's primary outcome has been published in VTI rapport 715. The present project was carried out by analysis of selected samples, multivariate evaluation, and improvement of the expert system's classification keys for granitoids and gabbroids. The system is currently based on 43 selectively chosen rock materials. The multivariate evaluation used PCA and PLS. The correlation (PLS evaluation) between petrographic and mechanical properties shows that for both granitoids and gabbroids, there are generally the same petrographic parameters that affect mechanical properties. The petrographic parameter for the granitoids having the greatest impact on the mechanical properties are: grain size, grain size distribution and mica content. The analysis also indicated a strong correlation between mica content and degree of foliation, which in turn results in a clear difference between magmatic and metamorphic granitoids. Concerning the gabbroids, it was frequency of micro fractures, mica content, grain size, and grain size distribution that had the greatest impact on the mechanical properties. The analysis indicated that the degree of metamorphism affects the resistance to abrasion from studded tires. Low metamorphic gabbroids show generally “lower” (better) Nordic ball mill values, compared to rocks of “higher” degree of metamorphism. Mica in gabbroids generally has a positive effect (more competent) on mechanical properties. Rock samples with “higher” mica content (5–-15%) generally have better mechanical properties than those with lower (>5%) mica content. The multivariate evaluation has proven to be a suitable tool to verify the mechanical properties' dependence on petrographic parameters.

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