Coefficient of consolidation measured by cone penetration tests in overconsolidated cohesive soils

Abstract

In offshore investigations, the dissipation test following penetration of a piezocone is extensively used in cohesive soils to obtain the consolidation behavior. Compared with that in normally consolidated soil, the dissipation response in overconsolidated silty clay or silt is more complicated, since the distribution of initial excess pore pressures and the subsequent dissipation depend on the overconsolidation ratio and partially drained conditions simultaneously. Large deformation finite element analyses within the formula of effective stress are carried out, where the large-amplitude displacement of piezocone under different drainage conditions and the dissipation are simulated. The large deformation approach is validated against centrifuge tests and cavity expansion solutions. A unique curve is established to estimate the nominal initial pore pressure at the shoulder of piezocone in overconsolidated soil, against a new normalized penetration rate. The curve is applicable to piezocone penetrations under different drainage conditions. The previous definition of operative coefficient of consolidation can be used to interpret the dissipation curves in overconsolidated soils as well. A unique backbone curve is proposed for overconsolidated soils to quantify the relationship between the operative and conventional coefficients of consolidation. A procedure is thus developed to determine in-situ conventional coefficient of consolidation of overconsolidated silty soils.