Visualizing the shallow failure mechanism of the T-Bar penetrometer

This paper presents a particle tracking method to visualize the deformation response of a soft soil due to the insertion of a T-bar penetrometer at shallow embedment depths. The T-bar is a type of full-flow penetrometer commonly used in centrifuge testing and offshore geotechnics to obtain the peak and remolded undrained shear strength profile of soft clay with depth. A series of T-bar penetration tests were conducted in Laponite RD, a transparent soil surrogate representing soft clay, to visualize the resulting deformations and the shallow embedment failure mechanism in the soil along the length of the T-bar during peak shear strength testing. The experimental set-up consisted of a laser-based computer vision capture system; a particle tracking algorithm was utilized to determine the deformation around the T-bar. Results of the experimental study showed a shallow embedment failure mechanism characterized by surface heave, gap formation, and gap closure above the T-bar. Tracked deformations were similar along the length of the bar with no deformation occurring past the axial ends of the bar. The deformations resulting from the particle tracking algorithm are consistent with previous numerical models of T-bar penetration with the exception that gap closure was observed along both the long and short axis of the bar indicating that plane strain may not be applicable at the ends of the bar.