Dublin’s geology is not uniform. You hit limestone gravel in one borehole and stiff boulder clay in the next. Last year we worked on a stormwater tunnel alignment near the Grand Canal where the contractor lost ground twice—not because of poor equipment, but because the transition between alluvium and glacial till had not been properly mapped. Tunnelling in Dublin means dealing with highly variable Quaternary deposits. The boulder clay itself can be dense and overconsolidated, but it often contains lenses of water-bearing sand and silt. A tunnel boring machine (TBM) that operates well in clay will struggle when it encounters a sudden change to granular material. We approach each project by building a detailed ground model from targeted site investigation. This data feeds directly into tunnel stability assessments, face pressure calculations, and settlement predictions. For Dublin Port tunnel conditions, the combination of soft-ground-tunnels analysis with in-situ permeability testing proves essential to avoid surface settlement in Docklands reclaimed land.
Dublin’s boulder clay is not homogeneous. Each lens of sand or silt inside the till mass represents a potential face instability that must be quantified before TBM launch.
