Publications

Excess pore water pressure has a significant effect on submarine slope stability and sediment deformation, and therefore, its in situ equilibrium measurement is crucial to carry out accurate slope stability assessments and to derive accurately design geotechnical parameters. In situ equilibrium pore water pressure is usually obtained from pore pressure decay during piezocone tests. However, submarine shelves and slopes are often characterized by the existence of low-permeability (fine-grained) sediments involving long dissipation tests which are an important issue for offshore operational costs. Consequently, short-term/partial dissipation tests are usually performed and in situ equilibrium pore water pressures are predicted from partial measurements. Using a modified cavity expansion approach, this paper aimed to predict for 4 different sites the in situ equilibrium pore water pressures. Comparison between predicted and observed in situ equilibrium pore water pressures allowed to define a guide to evaluate the minimum time required to perform short-term dissipation tests for a given marine sediment. The main finding of this note is that the second derivative of pore pressure, u, versus the logarithmic of time, t, must be positive in order to calculate accurately from partial measurements the in situ equilibrium pore water pressures.