During deep penetration, material from the upper layers is carried down with the penetrating object, thus affecting the bearing capacity at any given depth. This process has been modelled numerically, using a large strain finite element approach based on the Re-meshing and Interpolation Technique with Small Strain (RITSS) model. Three different shapes of penetrometer have been considered, namely T-bar (plane strain cylinder penetrating perpendicular to the cylinder axis), ball (axisymmetric) and thin circular plate. For all three objects, both smooth and rough interfaces have been considered. By comparing the steady-state bearing resistance with the soil strength profile, the effect of soil carried down with the penetrometer was quantified. This effect was expressed in terms of a depth offset to be applied to the real strength profile in order to evaluate the penetration resistance at any given depth. The results are applicable (a) to the interpretation of penetrometer data, and (b) to estimation of the bearing capacity profile for deeply penetrating foundation elements such as spudcans.
T-bar ball and thin circular plate are three alternative shapes of penetrometer that differ from the conventional cone penetrometer, in that they all allow flow of soil around them during penetration. Thus the net bearing resistance is measured directly without the need for corrections of overburden pressure due to the ambient stress field. Figure I shows sketches of the three penetration devices. For all penetration devices, the undrained shear strength, su, can be evaluated as (equation 1 shown in paper). In physical tests presented by Stewart and Randolph (1991, 1994), Watson et al. (1997, 1998) and Newson et al. (1999), a value of 10.5 has usually been adopted for the factor of T-bar, Nt, which results in good agreement between strengths deduced from Tbar, cone and laboratory tests.
