Pore-water pressure events during the in situ heat transfer experiment simulation: Piezometer probe technology

Single sensor piezometer probes, 8mm in diameter were developed and tested for deep-ocean geotechnical investigations in support of the Subseabed Disposal Program. Two probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi) during a scaled (0.28: 1) simulation experiment conducted at the David Taylor Naval Ship Research and Development Center (DTNSRDC) in Annapolis, Md. Testing was performed for 30 days with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. The piezometers sensed very small (approximately 1.7 kPa (0.25 psi)) pore water pressure events during the process of carrying out other experimental objectives. The pressure sensors exhibited excellent sensitivity and stability during other deep-ocean simulated laboratory pressure tests for periods of up to 750 hours. In addition to the measurements of ambient and dynamic pore pressure response to environmental forces, the piezometer test data can be used to derive the in situ undrained shear strengths and permeabilities of seabed sediments. The piezometer probe technology is providing a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits. 22 refs., 28 figs., 10 tabs.