DIFFERENTIAL PIEZOMETER PROBE FOR AN IN SITU MEASUREMENT OF SEA-FLOOR PORE-PRESSURE

A telemetering differential piezometer was designed and constructed at the Norwegian Geotechnical Institute to measure a minimum differential pressure (pore-pressure referenced to hydrostatic pressure) of 34 kPa and a maximum pressure of 294kPa in water depths of up to 500 m. An emplacement system was built at the University of Illinois. One successful in situ test in the Wilkinson Basin, in a water depth of 274 m, yielded a maximum excess pore-pressure of 59 kPa after the probe was driven about 3-2 m into the silty-clay bottom. An excess pore-pressure of 9-8 kPa was measured 5-10 h after emplacement of the probe. Implications of excess pore-pressures cyclically generated by storm and internal wave loading of sea-floor soils is discussed. It is concluded that a better understanding of submarine slope stability through the use of the effective stress principle should now be possible by measuring pore-pressure in situ.