Pore-Pressure Dissipation During Offshore Cyclic Loading

For cohesionless seafloor soils, the magnitude of pore pressures have a significant influence on design. As effective stresses control stiffness and strength characteristics for cohesionless soils, the rate of dissipation of pore pressures induced by cyclic loading will have a major influence on foundation deformations and seafloor stability. Four problems are examined: (1)Freefield earthquake response; (2)lateral soil-pile interaction; (3)wave loading of offshore gravity structures; and (4)wave induced seafloor pore-pressure response. Both published examples and new analytical solutions are used to show that significant pore-pressure dissipation may occur in many field loading problems, the extent of dissipation depending on induced pore-pressure gradients, the permeability of the soil, and the frequency of loading.