Evaluation of Empirical Equations for Assessing the true UCS of Rocks

The uniaxial compressive strength (UCS) of rocks is universally accepted design parameter in rock related projects. Therefore, ISRM and ASTM have published the standardized procedures for measuring the rock strength. In cases where the direct determination of the UCS may be impossible for anisotropic and weak rocks, indirect tests, point load (PL), Schmidt rebound number and sound velocity, are often employed to predict the UCS. Although a UCS test is known as simple to conduct it has often been reported as time consuming, requiring meticulously prepared rock cores and a laboratory. Thus, indirect methods have become inevitable since they are very practical for field applications. Although many works have been conducted to correct the size effect in PL tests it still needs improvements for a standardized PL strength. This study has reviewed the empirical equations derived from the results of previously published PL test results, has discussed the reasons of differences in formerly suggested prediction equations and proposed a PL-to-UCS conversion factor.