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The Cerchar abrasiveness test is a common testing procedure for the prediction of tool wear but consistent and detailed recommendations of the testing procedure are inexistent until now. One point of disagreement is the required number of scratch tests per sample to obtain reliable results depending on the grain size of the samples. The focus of this work was to verify the influence of grain size on the number of required single examinations per sample. Grain size analyses were performed to get sum-curves of each tested rock sample. From the grain size data the median and the interquartile range of the grain sizes were calculated. CAI values after 5 and after 10 scratch tests were compared with the median and the interquartile-range of the grain size. No grain size dependency of the CAI deviation between 5 and 10 tests in the analysed range was observed. Einfluss der Korngröße auf den Cerchar Abrasivitätstest IntroductionThe abrasiveness of intact rock or rock mass affects the wear behaviour of drilling, cutting and milling tools. Conducted research programmes by various scientists show that abrasiveness of rocks depends on different parameters (e.g. structure and texture, equivalent quartz content, Young's modulus). Index-tests directly prove the wear behaviour of intact rock and therefore allow rating the abrasiveness. In Western and Central Europe the Cerchar abrasiveness test is a common testing procedure for the prediction of tool wear due to the fast measurement process and the low costs. The only formal description of this test is the French Standard AFNOR, NF P94-430-1 [1]. The working committee AK 3.3 "Versuchstechnik Fels" of the German Association for Geotechnics presently is discussing more detailed recommendations for the Cerchar abrasiveness test. ObjectiveThe influence of geological parameters (e.g. equivalent quartz content, Young's modulus, structure, texture and mineral content) on the Cerchar abrasiveness index are well investigated The number of tests that should be performed on one rock sample is not yet defined in a standard. In previous studies different numbers of tests are requested. For homogeneous, fine-grained rock samples two or three scratch tests were originally suggested. Only at rock specimen with a grain size > 1 mm, five or more scratch tests per sample should be conducted [8]. Practical experience in testing has shown that 5 scratch tests on each sample should be accomplished to obtain a better defined and comparable mean value [5]. Recently published results propose 20 to 25 tests for granites and sandstones for a reduction of the standard deviation to 10 % [4], [9].Due to these different testing instructions a study on the influence of the grain size on the Cerchar abrasiveness index was performed. As the Cerchar abrasiveness testing length is amounting to 10 mm, the grain size of the samples could have an impact on the CAI value. For example, larger quartz grains with grain diameters up to or more than 10 mm must affect the CAI to a higher value. If grain sizes in a rock sa...

Abstract--The clay mineral distributions in fault gouges from shear zones in several slates, phyllites, mica schists, and gneisses of the Eastern Alps were statistically analyzed for consistencies in their occurrence. Discriminant analyses suggested significant groupings of the most common minerals: illite, smectite, kaolinite, and chlorite. The clay mineral distributions in the fault gouges appeared to be related to regional geological units. No relationship, however, was found with the piles of nappes of the Alps. The influence of the mineralogical composition of the parent rock on the clay mineral assemblages appeared to be minor, but the shear behavior of the parent rocks, which is mainly a function of rock strength, was found to control the formation of the clay minerals. In hard rocks (e.g., gneisses), solution transfer at an early stage of the shear process was apparently extensive enough to favor kaolinite formation. As shearing continued, the rate of solution transfer gradually decreased and favored the formation of smectite. In softer rocks (e.g., phyllites), the extent of solution transfer during the shear process was less than in the gneisses and generated an environment that favored smectite formation, even during the early stages of shearing.

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