Induced excess pore water pressures resulting from the insertion of piezometer probes of 8-mm (0.31-in.) diameter and a simulated waste canister of 102-mm (4.0-in.) diameter and the dissipation of these excess pressures were measured during deep-ocean component tests of the In Situ Heat Transfer Experiment (ISHTE). The sediment at the Pacific test site 1100 km north of Oahu, Hawaii, is an illitic clay.

Insertion-induced excess pore pressures were found to agree well with those predicted by models. Several aspects of the induced excess pressure dissipation were evaluated including the effects of probe and heater diameter, distal excess pore pressure response, and the synergistic excess pore pressure response from multiple insertions. The dissipation of induced excess pressures measured at each piezometer is predicted well by theory. The same analytical models predict the excess pore pressure history measured at the piezometers in response to the waste canister insertion. Present models were evaluated that predict insertion excess pressures and their dissipation rate at the probe surface and at distal, far field, points.