Ground Modelling Insights from Tonn Nua

A Data-Driven Approach to Site Understanding

Our studies combined academic and publicly available datasets (from our collaborations with Irish universities and public sources – e.g. INFOMAR, British Geological Society), with governmental data released by DCEE which included several geophysical survey datasets and, most recently, geotechnical data. Following each release, we carried out updated interpretation of the seabed and subsurface to ensure a thorough and seamless integration of all available data.

Using newly released geotechnical data, we correlated interpreted geological units with geotechnical parameters and developed a soil zonation model of the entire site. We also identified and analysed hazards and geohazards along with areas of outstanding uncertainty.

Seabed and Subsurface Conditions

The seabed at Tonn Nua is mainly covered by coarse sediments with isolated areas of sand. Distinctivefeatures such as sand waves (Figure 2), sediment ridges, and eskers (associated with the latest ice sheet advance in the region) were mapped across the site.

In the subsurface, several units were separated representing the bedrock and Quaternary sedimentary cover (Figure 3). The bedrock was interpreted as predominantly Palaeozoic in age and consisting of a series of lithologies. Limestone was the main rock lithology interpreted based on the available borehole data and literature with additional mudstone and sandstone domains delineated in the northwestern and eastern parts of the site. A sliver of Palaeogene limestone/sandstone was also interpreted along the southern boundary of the site.

Glacial sediments were interpreted directly on top of the Palaeogene to Palaeozoic bedrock, notably including thick till deposits, comprising high to ultra-high strength clays and dense to very dense sands. Overlying these older units, lacustrine to outwash plain (medium to very high strength / medium to very dense) and subglacial or proglacial fluvial (low strength) deposits were interpreted. A veneer of Holocene marine sands and gravels was inferred across the site based on literature.