Structural and mechanical characterisation of the Shale-Limestone Chaotic Complex formation of Santa Barbara open pit mine (Tuscany, Italy)

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Paolo Berry, Roberto Bruno, Daniela Boldini,
Abstract The mechanical and structural characterization of the Shale-Limestone Chaotic Complex (SLCC) bimrock of the Santa Barbara open pit-mine (Tuscany, Italy), was carried out by means of in-situ tests and image analysis.
The high slopes (about two hundred meters) of Santa Barbara open pit mine, cut in the SLCC rock mass, suffer large gravitational sliding movements. Due to the complex structure and variability of the SLCC the strength properties of the rock mass were investigated by non-conventional in situ-shear tests.
Moreover the parameters obtained by image analysis of pictures taken at the same scale of in the situ-tests were correlated to the mechanical properties of the rock mass.
The in situ non-conventional shear tests were designed in order to overcome the size limitation of laboratory test samples and namely to take into account the influence of calcareous blocks on the strength of the rock-mass. Test sample is prepared by isolating an 80x80x50 cm rock volume and an horizontal force is applied on the frontal steel plate until the failure of the sample occurs. The failure plane is investigated by laser-scan surveys and the strength parameters are evaluated according to the limit equilibrium method.
The digital analysis of photographic images of the SLCC rock mass focused on the evaluation of the marly-calcareous block-size distribution, and the identification of other image properties by advanced morphological modelling.
Finally the evaluation of volumetric block proportion within the clayey matrix was investigated by means of in-situ sieving tests on 1 m3 material samples.
The good correlation between the image properties and the strength parameters of the rock mass validate the proposed approach of integrating direct destructive measurements (non conventional shear-tests) by indirect non-destructive characterization (image-analysis).
Keywords: bimrocks, Image analysis, in-situ tests, Open pit mine, Slope stability
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