The Effect of Partial Drainage on Measurements by a Piezoball Penetrometer

Abstract

Full-flow penetrometers such as the T-bar and ball are now widely used in offshore site investigations to measure penetration resistance and then infer the strength properties of the seabed. To provide additional data on flow properties of the soil and increase the number of parameters that can be obtained from these tests, ball penetrometers fitted with pore pressure transducers, known as piezoballs, are now being used. Depending on the soil characteristics and rate of penetration, the soil conditions during penetration may vary from undrained to fully drained. The drainage condition during penetration will influence both the measured penetration resistance and excess pore pressure response and therefore influence any parameters interpreted. This paper examines the effect of drainage condition on piezoball measurements during penetration in a muddy silt sample collected from offshore Australia. Tests were conducted in the beam centrifuge at the University of Western Australia using a miniature piezoball, with pore pressure measurement at the equator position. The effect of drainage condition was examined by conducting tests at various rates of penetration, ranging from undrained to fully drained conditions. Methods of interpreting the results of a partially drained penetration test in order to deduce the undrained penetration resistance are also discussed.