A Multi-Sensor Piezometer for Shallow Marine Sediments in Coastal Environments
A multi-sensor piezometer has been developed to measure dynamic excess and ambient pore pressures in shallow marine sediments under the effect of surface waves, tides, and currents. The probe consists of a shaft (1.5 m long with five porous stones at subseafloor depths ranging from 0.10 to 0.93 m) and two upper chambers (one that is hermetically sealed for the transducer electronics and another that is hydraulically connected to the free water column). Pore pressures in the sediments under the effect of surface waves are measured with differential pressure transducers referenced to the mean water column pressure (cyclic component removed by a specially designed cyclic damping system). Field deployments of the probe follow a calibration and verification sequence to assure the proper function of all necessary components. This sequence involves laboratory and dockside calibrations using a static fluid reservoir technique and the measurement of differential pressures in the free water column prior to insertion. Calibration and pore pressure data from one deployment in 9.4 m of water off the Gulf of Mexico Coast near Biloxi, Mississippi show excellent precision and cyclic response.