Interpretation of piezoball dissipation testing in clay Available to Purchase

Full-flow penetrometers such as the cylindrical T-bar and spherical ball are now being used widely in soft seabed sediments due to their advantages of larger projected area and minimal correction for overburden pressure. A ball penetrometer fitted with one or more pore pressure transducers (piezoball) is of special interest as it can provide information on the soil consolidation properties by means of dissipation tests. Although analytical and numerical solutions have been developed to evaluate the undrained resistance factor for the ball, the absence of a similar theoretical basis has limited the use of piezoball dissipation testing. This paper provides the results of numerical analyses undertaken to model the excess pore pressure field generated during penetration of a piezoball, including its shaft, and the decay of pore pressure during a subsequent dissipation test. The analyses used a coupled large deformation finite-element (LDFE) method incorporating the modified Cam-Clay model. The robustness and validity of the LDFE analyses were verified by comparison with analytical and alternative numerical solutions of ball penetration and with experimental data from centrifuge model dissipation tests. The effects of soil properties and shaft–ball geometry on the dissipation response at two locations on the ball were studied. A normalised time factor for excess pore pressure dissipation, together with benchmark dissipation curves, are proposed for generic interpretation of the dissipation response around a piezoball.