Uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) are widely used in rock engineering. However, preparing standard samples for the strength tests may not always be possible for weak rocks. On the other hand, only rock fragments are available to estimate the rock strength in some cases such as drilling. Therefore, developing some models for estimating the rock strength from rock fragments will be useful. In this study, a crushability index (CI) was described from crushing test and the possibility of predicting UCS and BTS from this index was investigated. Strong and significant linear correlations were found between the CI and both the UCS and BTS. It is concluded that the UCS and BTS of rock can be estimated from the CI. The suggested method is especially useful for the drilling industry and for the cases where there are not enough samples for the standard tests.
The uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock is commonly used in civil and mining engineering projects performed in rock environment. However, the test for determining UCS or BTS is time consuming and expensive. On the other hand, it requires well-prepared and high quality core samples. For this reason, some indirect tests such as point load, block punch index test, Schmidt hammer, and ultrasonic velocity tests have been frequently used to predict rock strength for preliminary studies (Broch & Franklin 1972; Gunsallus & Kulhawy 1984; Gaviglio 1989; Sachapazis 1990; Katz et al. 2000; Kahraman 2001; Ulusay et al. 2001; Yasar & Erdogan 2004; Fener et al. 2005; Basu & Kamran 2010; Kohno & Maeda 2012 etc.). However, preparing standard samples for indirect test may not always be possible for weak or soft rocks. On the other hand, we may have only rock fragments to estimate the rock strength in some cases such as drilling. For this reason, developing some models for estimating the rock strength from rock fragments will be useful.
In this study, a crushability index (CI) was described and the predictability of UCS and BTS from the CI was studied. The sample preparation and testing method are easy in the crushability test. A small amount (500g) of crushed rock is enough for testing. This is an advantage when there are limited rock samples. That the crushability test can be applied on the drill cuttings is another important advantage.
A total of twenty four different rock types were sampled, eight of which were igneous, eight of which were metamorphic and eight of which were sedimentary. Quarries, marble factories, and natural outcrops in Nigde, Kayseri, Konya and Afyon areas of Turkey were visited and rock blocks were collected for the laboratory testing. The location and the name of the rocks are given in Table 1.