The estimation of undrained shear strength and remolded shear strength with full flow penetrometers requires the use of N values which are primarily derived experimentally. Four tests sites were studied to provide a basis for the evaluation of N. The data presented herein suggests trends relating N to sensitivity, liquidity index, and plasticity index. Intact and remolded N values are shown to be significantly different. Relationships between the ratio of intact and remolded penetration to sensitivity are presented.
Full flow penetrometers were introduced in the early 1990s for strength profiling of centrifuge test samples. They were designed to provide higher resolution than conventional cone penetrometers and eliminate correction necessary for overburden pressure. Currently full flow penetrometers are used primarily offshore to profile soft clays, providing a profile of penetration resistance. Remolded penetration resistance can be measured by cycling the probe about a desired depth. Flow of soil around the penetrometer as it is cycled over a depth increment effectively remolds the clay. Both intact and remolded undrained penetration resistances can be used to calculate shear strength values based on experimentally validated N values. N values for both intact and remolded strengths are presented and compared in this paper. Additionally, the effect of sensitivity and liquidity index on values of N is investigated.
Full flow penetrometers, including the ball and t-bar, offer several advantages to conventional methods used for the in situ estimation of penetration resistance and undrained shear strength such as the cone penetrometer (CPT) and shear vane (FVT). Corrections for overburden and pore pressure are not necessary, closed form analytical solutions exist, and the larger projected area (typically 100 cm2 compared to 10 cm2 for the CPT) allow for a more accurate measurement in low strength soils.
