Hydraulic Failure and soil-structure deformation due to wave and draw down loading

In engineering practice submerged soils are commonly considered to be saturated and consequently the pore fluid may be regarded as incompressible. At shallow water depths this two-phase model is not in accordance with natural conditions. Even small quantities of gas bubbles change the stiffness properties of the pore fluid dramatically. In response to external fluctuating pressures, the gas bubbles in the pores experience a volume change, thus causing local transient flow. The latter must be consistent with the permeability law of the soil. Based on Biot's consolidation equation, both uncoupled and coupled numerical simulations and analytical estimates have been employed, demonstrating that time-varying pressure loading contributes to soil deformation, fluidization and hydraulic failure. A variety of geotechnical situations is reviewed. These include rapid draw-down, wave loading and turbulent water current acting on both a protected or unprotected sandy soil bed in shallow water. The actual pore pressure response of the submerged subsoil has been calculated. It is demonstrated that this loading contributes to sand bed deformation, fluidization and associated failure. The vulnerability to erosion and scouring is emphasised.