In Newbridge, the transition from the Curragh's sandy gravels into the limestone bedrock beneath the town creates a challenging profile for any excavation deeper than four metres. We regularly encounter interbedded layers of stiff glacial till sitting directly on pinnacled rockhead, which can deflect an excavation support system if the pre-construction ground model is too simplified. A solid geotechnical design has to account for this erratic boundary, especially where the River Liffey tributaries have reworked the upper deposits. Getting the CPT test data calibrated against rotary cores is what stops surprises during bulk excavation, and it is the first step we enforce before any shoring layout leaves the office.
In Newbridge, the limestone bedrock is rarely flat—pinnacles and clay-filled fissures can reduce passive resistance by 40% if not mapped in the ground model.
