In-Situ Observation of Wave-Induced Pore Water Pressure in Seabed Silt in the Yellow River Estuary of China
Xing Du, Yongfu Sun, Yupeng Song and Chaoqi Zhu
Variation of pore water pressure in soil grains, caused by the force of waves repeatedly acting on the seabed, is the main reason for soil liquefaction. In the study of wave-induced pore pressure response, field monitoring is closer to the real situation than other research methods. In this study, pore pressure in the easily liquefied zone of the Yellow River Estuary was measured in a long-term, high-precision way using self-designed pore pressure observation equipment. Both total and excess pore pressure were analyzed by comparison with the hydrodynamic conditions. Results showed that the total pore pressure was influenced by waves and tides, whereas excess pore pressure was influenced only by waves. Transient liquefaction occurred at a seabed depth of 0.5 meters (m), but no residual liquefaction occurred during the observation period. The maximum depth at which waves influenced pore pressure was between 0.5 and 1.5 m.
The factors influencing pore pressure and the reason there was no residual liquefaction are discussed. The effects of pore water pressure response are mainly determined by the relationship between hydrodynamic action and the soil’s liquefaction resistance. By comparing normalized in situ observation data and water flume test data, we found that the effect of waves on pore water pressure under actual marine conditions is much smaller than that in water flume tests with equal scale reduction. To better represent the wave-induced pore pressure response results, the relationships between pore pressure increments induced by waves and decrements due to seepage are summarized in a graph and divided into three categories: no response, oscillatory without accumulation, and affective accumulation.
Keywords: Yellow River Estuary, wave-induced pore pressure, pore pressure observation, silt liquefaction