LANCELOT - AN IN-SITU PIEZOMETER FOR SOFT MARINE-SEDIMENTS

Lancelot is a tethered marine piezometric probe designed to penetrate the seabed at full-ocean water depth to obtain consolidation and permeability data as well as to constrain the effective stress state through the measurement of equilibrium pore water pressure. Probe design is reviewed, highlighting its rapid deployment and recovery capabilities. Example data are shown from recent deployments on the St. Pierre Slope, southwestern Grand Banks of Newfoundland, including one within a debris flow. Sites were investigated that were thought to possess excess pore water pressures, based on previous mapping of seabed pockmarks and gas-related features. Lancelot measurements confirmed this at the debris flow site, where conditions were essentially still liquefied.