Measurements of wave‐induced pore pressure in submarine sediments under various marine conditions

Abstract

Abstract Wave‐induced pore pressures were measured at four sites around Shimizu Harbor, Central Japan. At Site 1 the measurements of the wave‐induced seafloor pressure and pore pressure at a depth of 0.5 m below the mud line were conducted in about 14 m of water. The sediment was silty sand with a permeability of 4 × 10−5 m/s. The pressures induced by wind waves with about a 10‐s period were transferred through the sediment to the pore pressure with damping of about 4% through 9% and time lag of 0.1 rad (0.2 s) through 0.16 rad (0.3 s). The wave‐induced seafloor pressure and pore pressure changed differently in the breaker sediment. At Site 3 absolute and differential piezometers were installed in sand and gravel sediment at depths of 0.7 m and 0.5 m, respectively, in about 1.7 m of water. The pressure attenuation was about 1% for the tide without time lag. The piezometers used at Sites 1 through 3 were a transformer type. At Site 4 a new probe of semiconductor type was tested in sand and gravel sediment at a depth of about 0.4 m below the mud line in about 0.7 m of water. The seafloor pressure of periods of 1.5 s through 20 s was transferred to the pore pressure, being diminished by 85% through 45%. The wave pressure at the seafloor was transferred through the submarine sediment to the pore pressure with greater damping than predicted by current theory for the saturated sediment (Madsen, 1978; Yamamoto, 1981) and in some cases delay. The magnitude of damping increased with the decrease in the length of waves.