Applicability of "Full-Flow" Penetration Probes for Characterizing Soft Soil Deposits

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Soft soil sediments, primarily due to their high sensitivity, underconsolidation and very low strength, present a unique challenge to the geotechnical community in both their characterization and use as an engineering material. Conventional drilling and in situ testing methods do not quantify soft sediments at a level of accuracy and reliability now required for many geotechnical projects. While performance modifications can be made, these in situ devices are restricted by inherent characteristics of their test procedure and/or geometric design that cannot be overcome through minor improvements. The insufficiency of these methods is compounded by steady increases in the quantity and complexity of on-shore, near-shore, and off-shore soft sediment applications such as tunnels, bridges, wind turbines, submarine slope stability, buried pipelines, and oil and gas platforms. This project is focused on a unique and important opportunity to validate the ability of "full-flow" penetrometers to characterize soft soil deposits through leveraging the resources of five existing highly characterized international test sites. "Full-flow" penetrometers provide a measure of the pressure differential necessary to induce soil flow around a symmetric geometric probe. In principal, the penetrometers are akin to a viscosity measurement as they induce plastic flow of the soil around a geometric probe during penetration. This unique flow measurement is free from the correction factors that limit the accuracy of state-of-practice devices and therefore have strong potential in the applications mentioned above. To date, three types of "full-flow" penetrometers have been evaluated (T-bar, ball, and plate) though analytical, numerical, laboratory, and centrifuge investigations. From these analyses, "full-flow" penetrometers demonstrate potential to obtain profiles of the undrained shear strength (su) and the remolded shear strength (su-remolded) respectively, which in turn provide an in situ estimate of sensitivity (St). Through performing "twitch" tests, a series of consecutive short penetrations where the penetration rate is sequentially halved, an in situ estimate of the coefficient of consolidation (cv) may be obtained. "Full-flow" penetrometers will be validated at full-scale through an extensive field investigation at five highly characterized test sites, three in North America, one in Norway, and one in Australia, in a cost-effective manner. The field testing program at each site will consist of performing a minimum of 13 soundings, selected excavation of the penetrometers to verify flow patterns, and limited sampling for validation of the applicability of existing data. This will culminate in the validation/development of interpretation methods and procedural guidelines for "full-flow" penetration probes. The broader impacts of this proposal include the potential to affect worldwide soil engineering practice with respect to site investigations and the design of geosystems on-shore, near-shore, and off-shore including the applications listed above. The use of international test sites and collaboration with international experts on in situ testing ensures broad applicability and dissemination of the research findings. The results of this research will be posted on the PIs website, presented at conferences, and published in journals in a timely manner.