Using indentation test to compute rock brittleness index

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Measuring rock brittleness value is very crucial for underground excavation in rock mass. It is not easy to measure rock brittleness with standard laboratory condition in present. Therefore, the rock brittleness value was obtained as an empirical function of uniaxial compressive strength and Brazilian tensile strength. Indentation test is the method to investigate hardness, toughness, drillability and brittleness properties of rock. NX core size (54 mm) rock samples, with a height to diameter ratio at least one, are used for the test. Top and bottom of the specimen are saw-cut; so it is smooth and free of irregularities. The test specimen were confined with gypsum cement (plaster) within steel cylinder frames approximately 115 mm in diameter and top of the rock sample is at the cementing agent level and be positioned perpendicular to the indentor that is penetrated with constant loading speed (0.00254mm/sec). The test are performed with MTS machine with in 300 ton capacity. Afterward, the force applied on surface of rock sample and the indentor begins to penetrate rock till the test stopped and the applied force and relevant penetration were recorded in computer base. Using dataset including force and penetration, force-penetration chart could be obtained. In this chart, relations between force and relevant penetration could be evaluated and hardness, brittleness or drillability of rock can be computed. In this study, the methods to compute relevant rock properties by performing indentation test were examined. Besides that, computing rock brittleness via indentation test was evaluated. As result of research, using database (i.e., uniaxial compressive strength, Brazilian tensile strength, rock density and brittleness values from indentation test) obtained from 48 hard rock tunnel projects; rock brittleness index and classification were suggested for underground excavation. It is concluded that the indentation test could be used directly for computing rock brittleness t increases with excavability of rock.
Original languageMultiple languages
Number of pages1
Publication statusPublished - 2009
Event62th Geological Congress of Turkey - Ankara, Turkey
Duration: Mar 13 2009Mar 17 2009


Conference62th Geological Congress of Turkey
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