Determination of the coefficient of consolidation by piezocone tests under partially drained conditions

Abstract

Dissipation tests after piezocone penetration are used widely to estimate the consolidation behaviour of cohesive soils. Interpretation of dissipation tests is complicated in intermediate soils, such as in silts and silty clays, since the accumulated pore pressures and the subsequent dissipation response are affected by the partially drained conditions. The influence of partial drainage on dissipation response is investigated using a large-deformation finite-element approach within the framework of effective stress analysis. The numerical approach is validated by comparison with the existing centrifuge tests where dissipation tests were performed after undrained and partially drained penetrations. The numerical results provide insights to quantify the effects of drainage conditions, including distribution of pore pressures prior to dissipation and then the operative coefficient of consolidation, ch, against various penetration velocities. The time corresponding to a given degree of dissipation is found to be increased with reducing normalised penetration velocity, as the gradients of normalised pore pressures are reduced in the radial direction before dissipation. The ratio between ch and the coefficient of consolidation can be described through a unique backbone curve. A new approach estimating the coefficient of consolidation from a dissipation test following partially drained penetration is proposed for practical applications.