Small strain and large strain FE analyses have been carried out to detect the effects of various in-situ factors on the limiting resistance of cylindrical T-bar and spherical ball penetrometers in homogeneous cohesive soil obeying a Tresca or Von Mises failure criterion. The results confirm that the soil rigidity index has no influence on the ultimate bearing resistance for either T-bar or ball, but only on the penetration needed to reach the limiting resistance. As expected, rougher penetrometers result in higher soil resistance, ln-situ stress anisotropy probably has slight influence as indicated by large strain analysis. Once the embedment exceeds a certain depth, there is little difference between small strain and large strain analysis and the bearing resistances for different preembedments tend to converge. The Von Mises failure criterion was found to give 10 % smaller bearing resistance for the ball penetrometer than that obtained with the Tresea criterion.
In-situ testing is playing an increasingly important role in site investigations because of the difficulty in obtaining undisturbed samples from deep water sites. Currently, the most common technique used to determine the strength profile offshore is cone penetrometer testing (CPT), which produces a continuous profile, coupled with vane shear testing at discrete intervals. However, the limitations in the low sensitivity of the cone and the large corrections required for the raw measured cone resistance have led to the development of aitemative penetrometers, including cylindrical T-bar and spherical ball penetrometers (Randolph ct al, 1998; Newson et al, 1999). Fig. I shows schematically the mechanisms of soil flow around cone, T-bar, and ball penetrometers. The (near) full flow around the latter two types of penetrometer leads to the double advantage of relative independence from the ambient overburden stress, and the ability to derive exact plasticity solutions for the limiting bearing resistance.