Predicting the compressive and tensile strength of rocks from indentation hardness index

TLDR: In this paper, a simple and easy indentation hardness test is proposed to predict the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock for designing surface and underground structures.

Abstract: Rock engineers have commonly used the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock for designing surface and underground structures. Determining these rock strengths is timeconsuming and expensive, particularly for the preliminary studies of projects. For this reason, indirect tests such as Schmidt rebound number and, ultrasonic test are often used for predicting rock strength. Since indirect tests require less or no sample preparation and the testing equipment is less sophisticated, these tests are very easy to carry out. In addition, these tests can usually be performed in the field. The indentation hardness test is a simple and easy test and can be conducted using a point load test apparatus. The test is of particular value when only a limited amount of rock material, e.g. a thin disc of core or a small lump sample, is available1. The UCS and BTS can easily be predicted from the indentation hardness index (IHI) for the preliminary investigations, if strong predictive correlations are established. Since rock indentation is the basic process in drilling and boring, numerous researchers2–16 have carried out indentation tests to understand the indentation phenomena or to develop prediction models for drilling or boring. Kahraman et al.15 also investigated the relationships between the slope of load-indentation curves and the rock properties. They found good correlations between the slope of load-indentation curves and the rock properties. Kahraman and Gunaydin17 investigated the sawability prediction of carbonate rocks from indentation hardness tests carried out by attaching a dial gauge to the point load apparatus for measuring penetration. They concluded that the indentation hardness test can be used for predicting the sawability of carbonate rocks. Recently, Yagiz18 suggested a new brittleness index and rock brittleness classification based on type, strength, and density of rock together with the results of punch penetration tests. A standard indentation test was recommended by ISRM1 and Equation [1] was suggested for the prediction of UCS from IHI