SUMMARY:

The Uniaxial Compressive Strength (UCS) is widely used by professional engineers who work in designing surface or underground structures in geologic materials. This parameter is used to determine rock properties and characteristics. Moreover, it is important not only to analyze but also to study the rock in geological and geotechnical perspectives. The UCS of intact rock is a necessary input for the estimation of rock mass strength. However, the UCS test is very expensive and demands strictly prepared high quality samples. Thus, this parameter is often determined based on the results of other tests including Brazilian Tensile Strength (BTS) and Point Load (PL). Previous scientific studies indicated that the BTS relates better with UCS than does PL. The previous studies produced somewhat inconsistent conclusions - some authors found a better linear correlation and others a better non-linear correlation between UCS and BTS. Thus, this study was carried out to figure out a better correlation between UCS and BTS for each rock type and a general equation for all types of rock. This paper analyzes previous studies about such correlations, and provides additional analyses using the database of the Earth Mechanics Institute (EMI) in the Department of Mining Engineering at the Colorado School of Mines (CSM). These data have been collected over more than 40 years of rock testing at EMI. In total, 316 tests were used for this analysis including 158 tests of BTS and 158 tests of UCS. To analyze the data, linear and non-linear correlations were used. In this study, the non-linear correlation showed a better correlation for two types of rocks (e.g., igneous and metamorphic), but this correlation was poorer for sedimentary rocks. The diversity and directionality of rocks can cause some issues in the rock strength analysis. In fact, rocks with the same mineralogy can give a different strength test value due to its porosity, weathering, or the presence of micro-fissures.

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