Piezometer Probes for Assessing Effective Stress and Stability in Submarine Sediments

Abstract

Multisensor piezometer probes were deployed at four different sites in the Mississippi Delta in water depths ranging from 13.5 to 43.6 m with sensor penetration depths of up to 15.6 meters. Absolute and differential pressure sensors were used to measure pore water pressure and excess pressures, respectively. The free water column pressure was measured with absolute pressure sensors. Pore pressures induced by probe insertion were determined as well as ambient excess pore pressures following the time-dependent decay of induced pressures. Significant differences in the pore pressures and related geotechnical properties were found between East Bay and Main Pass sediments. Generally higher probe insertion pressures and lower ambient excess pore pressures were characteristic of Main Pass compared to East Bay. Probe insertion pressures (Ui) were found to correlate well with the undrained shear strength (Su) of the sediments, indicating reasonably good agreement with the predicted relation: Ui = 6Su as suggested by an earlier study42. Using this relationship undrained shear strengths were calculated and compared with measured values.