A pore-water pressure probe (piezometer) was implanted in Mississippi delta sediments at a preselected site (Block 28, South Pass area, 29°00´N, 89°15´W) 145 m from an offshore production platform (water depth approx. 19 m) in September 1975. Total pore-water pressures (uw) were monitored for extended periods of time at depths of approximately 15 and 8 m below the mudline concurrently with hydrostatic pressures (u8) measured at depths of 15 m and approximately 1 m below the mudline. Relatively high excess pore-water pressures, ue = (uw -u8), were recorded at the time of probe insertion measuring 99 kPa (14.4 psi) at 15 m and 50 kPa (7.3 psi) at 8 m. Six hours after the probe was implanted, excess pore pressures were still high at 81 kPa (11.8 psi, 15 m) and 37 kPa (5.4 psi, 8 m). Pore pressures appeared to become relatively constant at the 8-m depth after 7 h had elapsed, and at the 15 m depth after 10-12 h. Excess pore-water pressures averaged 72 kPa (10.4 psi, 15 m) and 32 kPa (4.6 psi, 8 m) prior to the initial effects of Hurricane Eloise, which passed in close proximity to the probe site. Significant variations in pressures were recorded during storm activity. As the effects of the storm subsided, excess pore-water pressures began to decline slightly at the 15-m depth; however, concurrently at the 8-m depth, pore pressures began to increase gradually. During the period of 21-25 days after the probe was implanted, excess pore pressures appeared to become more constant, averaging 24 kPa (3.5 psi) at 15 m and 43 kPa (6.2 psi) at the 8-m depth. The presence of methane, a common occurrence in these delta muds, may have influenced, or contributed to, the total pore-water pressures measured during this experiment.
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