Bryan Anthony McCabe

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 ) I _s(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 I _s(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. I _s(50) values (from the unfiltered database) were found to be independent of loading direction (axial or diametral). An initial attempt to correlate UCS with I _s(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 ( U C S = 20.36 I s ( 50 ) 0.665 ) agrees well with the expression UCS = 20 I _s(50) currently in use for Dublin granites up to UCS ∼30 MPa but renders UCS = 20 I _s(50) to be unconservative at higher strengths.

Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of an oversized driving shoe introduces additional complexities influencing shaft resistance mobilisation, over and above those applicable to preformed displacement piles. Therefore, several design codes restrict the magnitude of shaft resistance in DCIS pile design. In this paper, a series of dynamic load tests was performed on the temporary steel driving tubes during DCIS pile installation at three UK sites. The instrumented piles were subsequently subjected to maintained compression load tests to failure. The mobilised shear stresses inferred from the dynamic tests during driving were two to five times smaller than those on the as-constructed piles during maintained load testing. This was attributed to soil loosening along the tube shaft arising from the oversized base shoe. These radial stress reductions appear to be reversible by the freshly cast concrete fluid pressures, which provide lower-bound estimates of radial total stress inferred from the measured shear stresses during static loading. This recovery in shaft resistance is not recognised in some European design practices, resulting in conservative design lengths. Whilst the shaft resistance of DCIS piles was underpredicted by the dynamic load tests, reasonable estimates of base resistance were obtained.

Buried karst features result from a complex interplay between carbonate bedrock and structural geology. The enhancement of carbonate aquifers through this interplay creates hydrogeologically complex subsurface drainage networks and highly variable surface topographies. This article reports on the sediment fill and fossil pollen record from a large enclosed negative karst landform at Coolough, near Galway City in the west of Ireland. The landform was discovered during the preliminary site investigation for the proposed N6 Galway City Ring Road. Major joint sets developed in the Carboniferous (Mississippian) Limestone bedrock govern the local hydrogeology and structural evidence suggests that a local fault has controlled the east–west propagation of the deep enclosed depression. Fluvial and lacustrine palaeoenvironments are interpreted from the sediments infilling the enclosed depression, within which three discrete diamicts are identified, potentially representing distinct phases of glaciation. Pollen assemblages, which reflect palaeoenvironments of open woods and grasslands, have been correlated with other deposits in Ireland and Europe and suggest a minimum date of the Early Pleistocene for the oldest of the diamicts, and thus an upper age limit on the development of the karst depression. Fluvial disturbance to the deposit is evident and is likely to be responsible for the chronological discrepancy between the Early Pleistocene and Middle Pleistocene sediments both recorded from the deposit infill. The findings of this multidisciplinary study contribute to an understanding of Quaternary landscape evolution in western Ireland.