Estimation of Stress History by Partial Piezocone Dissipation Tests

In a Piezocone Penetration Test (PCPT or CPTu), the probe can be stopped at a desired depth during penetration, and the excess pore pressure generated around the cone can be measured as dissipating u_t versus time, t. Using the rate of dissipation, it is possible to estimate the value of the soil deposit's coefficient of consolidation and thereby determine changes in hydraulic conductivity. Theoretically the dissipation is complete as u_t approaches in-situ equilibrium pore pressure, u₀. In fine-grained soils time required for complete dissipation or even 50% dissipation maybe very long, making the test impractical. The in-situ (equilibrium) pore pressure, u₀, can be estimated from a partial dissipation record requiring a shorter dissipation, by extrapolating the measured u_t data on an inverse time scale (i.e. u_t against l/t). Based on this partial dissipation test, the stress history (or the status of the consolidation) of the soil deposit can be evaluated. However, no case study has been reported in open literature where the extrapolation method has been applied to estimate unknown stress history of soil deposits. In this paper, this methodology was applied to a dredge disposal area to obtain soil parameters related to stress history as well as soil deformation due to consolidation.