Accurate determination of soil in situ shear strength using the T-bar penetrometer requires full understanding of the soil flow characteristics around the T-bar, including the three-dimensional soil flow near the ends of the T-bar. The conventional plane strain solution of the T-bar resistance factor ignores the shearing that takes place around the ends of the T-bar, thus may blemish the accuracy of the interpretation. A three-dimensional finite element model has been built to investigate the end effect of the T-bar on its flow mechanism and resistance factor. The effects of the T-bar aspect ratio and surface roughness on resistance factor are explored extensively. A new interpretation formula of the T-bar resistance factor is proposed as a function of the T-bar aspect ratio and roughness.
The recent exploration of hydrocarbon fields in deep water has placed more reliance on in situ testing, such as vane shear testing and push-in penetrometer testing, due to the difficulty and high cost of obtaining high-quality soil sample for laboratory testing. The T-bar penetrometer was initially developed for characterizing soft fine-grained soils in centrifuge testing (Stewart and Randolph, 1991) and has been adopted in the field for site investigation since the 1990s (Stewart and Randolph, 1994). Compared to the conventional push-in penetrometer, i.e. cone penetrometer, the advantage of the T-bar penetrometer includes:
a 5~10 times larger projected area, leading to higher resolution of penetration resistance in soft sediments;
negligible effect of overburden pressure and soil rigidity index on penetration resistance due to the full-flow mechanism (Lu, 2004, Zhou and Randolph, 2009).
The T-bar penetrometer comprises a cylinder bar attached perpendicularly to the end of a smooth shaft, where a load cell has been embedded, as shown in Fig. 1. Along with increasingly being used in offshore in situ site investigation, T-bar is also frequently used for soil strength determination in laboratory and centrifuge tests (Hossain et al., 2005, Dingle et al., 2008). Therefore, an accurate interpretation procedure of the T-bar data is of great interest to the geotechnical community.
