When the CPT rig arrives on a site outside Portlaoise, the first thing our team does is calibrate the piezocone against the local water table, which in this part of the Irish midlands can sit surprisingly high within the glacial till. We run a dissipation test right at the depth where the silt transitions into fine sand, because that contact zone is exactly where excess pore pressure builds during a seismic event. It is methodical work, watching the pore pressure decay curve flatten on the screen, and it tells us more about the drainage capacity of the ground than a dozen borehole logs. In the lab, we couple that field data with cyclic triaxial tests on reconstituted specimens, applying the loading frequencies that match the seismicity recorded by the Irish National Seismic Network for the Laois region. The setup itself is unglamorous—a triaxial cell, some latex membranes, a back-pressure system—but the output defines whether a foundation in central Portlaoise needs ground improvement or can proceed as designed. For sandy layers beneath the Triogue River floodplain, we often cross-check our CPT data with a grain size analysis to confirm the fines content, which is the single most influential factor in liquefaction susceptibility.
In the layered glacial deposits around Portlaoise, a clean sand lens at four metres depth can liquefy while the overlying till remains intact—spotting that contrast is what the analysis is built for.
