Pore-pressure generation in cyclic T-bar tests on clayey soil

A model miniature T-bar penetrometer, designed for in-flight applications at the COPPE geotechnical centrifuge in Rio de Janeiro, Brazil, comprises a cylindrical crossbar of 15·2 mm diameter and 112·5 mm long, attached at right angles to the end of a vertical shaft. During penetration, the resistance is measured by a sensitive load cell situated at the vertical shaft immediately above the crossbar. Additionally, a set of two Kulite miniature pore-pressure transducers have been inserted inside the cylindrical crossbar, one at each side of the vertical shaft, facing the bottom part of it. This paper presents a set of cyclic T-bar penetration tests carried out on an artificial clayey soil made of 20% bentonite and 80% kaolin. The generated excess pore pressures are measured at both sides of the bar during the penetration cycles, and compared with values found in the literature. The maximum excess pore pressure, as well as the peak soil resistance, show a significant decrease during soil cyclic penetration. The variations in the excess pore pressure due to the cyclic penetration of the T-bar were also monitored using additional pore-pressure transducers, which were fixed at the bottom of the soil layer. The results were compared with the measurements obtained from the pore-pressure transducers located on the cylindrical crossbar.