A MULTISENSOR 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 effe ct of surface waves, tides, and currents. The probe consists of a shaf t (1.5 m long with five porous stones at sub-seafloor depths ranging f rom 0.10 to 0.93 m) and two upper chambers (one that is hermetically s ealed 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 press ure transducers referenced to the mean water column pressure (cyclic c omponent removed by a specially designed cyclic damping system). Field deployments of the probe follow a calibration and verification sequen ce to assure the proper function of all necessary components. This seq uence involves laboratory and dockside calibrations using a static flu id reservoir technique and the measurement of differential pressures i n the free water column prior to insertion. Calibration and pore press ure data from one deployment in 9.4 m of water off the Gulf of Mexico Coast near Biloxi, Mississippi show excellent precision and cyclic res ponse.