While the Uniaxial Compression Strength (UCS) test is the gold standard for determining the UCS of rock for geotechnical and mining applications, empirical correlations between UCS and other test measurements such as Point Load Index (PLI) Is(50) values are useful in situations where intact cores are difficult to retrieve and/or the scope of UCS testing is constrained by budget. In this paper, an extensive database of UCS and PLI Is(50) values has been compiled for the Upper Liffey Valley and Northern Units of the Leinster Caledonian granite in Dublin, Ireland. UCS values in the full (unfiltered) database correlated statistically with bulk density but were independent of specimen geometry. Statistical analysis also detected some UCS dependence on formation type but none on weathering, although important caveats apply to these findings. Is(50) values (from the unfiltered database) were found to be independent of loading direction (axial or diametral). An initial attempt to correlate UCS with Is(50) exhibited unacceptable scatter, prompting a systematic filtering process, with strict criteria for UCS specimen diameter and aspect ratio, specimen position within the core and the application of Grubbs process to identify outliers. This provided a significantly more reliable correlation based on ≈20% of the original dataset. A power correlation was found to capture the form of the data better than a linear one. This new correlation (UCS = 20.36Is(50)0.665) agrees well with the expression UCS = 20Is(50) currently in use for Dublin granites up to UCS ≈30 MPa, but renders UCS = 20Is(50) to be unconservative sat higher strengths.

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