Field tests suggest that the T-bar factor may vary over a large range for calcareous soils. As the T-bar penetrates very deep into soft soil, a full flow-round mechanism is formed around the T-bar. Examining the stress states around this mechanism suggests that soil elements are subjected to a varying stress state, and the element behaviour represents a combination of triaxial compression, simple shear, and triaxial extension conditions. This paper reports results of T-bar penetrometer tests performed at an elevated gravity of 150-g (where g is earth's gravity) in a geotechnical centrifuge on a calcareous silty sediment collected from the North West Shelf of Australia. Once the centrifuge tests were completed, a tube sample was cored from the centrifuge strongbox. Two specimens were prepared from two reference depths, and undrained monotonic simple shear tests were carried out. The undrained shear strengths obtained from the simple shear tests were used to back analyse the T-bar bearing factor (NT-bar). A mean T-bar factor of 9.92 was found for the calcareous silt tested. A threedimensional large deformation finite element analysis was conducted to find out the T-bar factor in an ideal soil, showing the potential for undertaking further parametric analyses using an appropriate constitutive model to develop a robust interpretation framework for Tbar test data.
Full-flow penetrometers (such as the T-bar, ball) are increasingly practiced both in laboratory environments (e.g. Purwana et al., 2005; Hossain et al., 2011) as well as in field investigations offshore (Erbrich & Hefer, 2002; Erbrich, 2005) due to its ability in: (i) providing a continuous resistance profile that can be directly interpreted to the corresponding soil strength profile; and (ii) eliminating the necessity of overburden pressure corrections needed for the cone penetrometer (Lu et al., 2004; Zhou & Randolph, 2009). The T-bar penetrometer was first implemented by Stewart & Randolph (1994), and identified as advantageous for investigating fine-grained sediments due to the large projection area ratio (5∼10 times larger than the cone penetrometer) leading to high resolution of soft seabed resistance. T-bar penetrometer tests allow any stratigraphy variance to be captured through measurements of the load through an attached load cell located just above the T-bar (Fig 1a). Depending on the penetration speed of the Tbar both undrained and drained strength can be inferred from the measured load (Finnie & Randolph, 1994).
