Predicting uniaxial compressive strength of building stone based on index tests: Correlations, validity, reliability, and unification

Uniaxial compressive strength (UCS) is of great importance for building stone. Index tests have been widely used to quickly predict UCS due to the cumbersome and expensive measurement of UCS. The paper presents a state-of-the-art review of the current understanding of those index tests. Emphasis is placed on recording the four frequently used point load, Schmidt hammer, sound velocity and Brazilian test. In particular, those four index tests are initially introduced by exhibiting experimental apparatus and standard testing methods. This is followed by a review of various corresponding methods (including regression analysis, machine learning, and numerical simulation) for correlating UCS to index tests. Subsequently, the paper provides a summary of validity studies of index tests in the UCS estimation by eliminating the effects of rock heterogeneity. Also, how index tests and their correlations with UCS respond to the rock heterogeneities is examined to know the reliability of estimated UCS. Then, the possibility of unifying the numerous correlations for predicting UCS via index tests is explored based on the previous mass data. Throughout the presentation, the current overall gaps in understanding four index tests are identified by the research community in an attempt to stimulate further research in these promising directions.