Indentation test for the measurement of rock brittleness

Abstract

Rock brittleness is an important rock characteristic, pertinent to predicting rock fragmentation behavior, energy consumption in rock cutting, and selection of proper cutting geometry. While brittleness is typically well understood as a concept, there is no universally accepted measure for this rock characteristic and often a combination of rock properties are used to define brittleness rather than single test to make a direct measurement. Typically, rock brittleness is defined indirectly as a function of uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock through empirical formulas. This could be a simple ratio of UCS to BTS or any combination of these two measured physical properties along with fracture properties of the given rock type. This shows the need for alternative testing methods that can be used for measuring brittleness in a more or less direct method. One of the tests that could be considered for measurement of brittleness is indentation test. This test has been used for evaluation of rock hardness and drillability and can be considered for measuring the rock brittleness. In this study, the results of a series of indentation (or punch) tests are used to compute rock brittleness. A brittleness index is introduced from the analysis of the results of indentation test on a variety of rock types and a classification for rock brittleness is suggested for application in rock excavation. Copyright 2012 ARMA, American Rock Mechanics Association.