abstract
In-situ Determination of Peak and Remoulded Strength Using Full-Flow Penetrometers. Accurate and precise measurement of the peak and remoulded strength is critical for the assessment of geohazard stability and for the design and performance of all structures founded in soft sediments. Unlike onshore characterization, offshore sediment characterization is complicated by significantly higher cost per hourof investigation and execution and resolution limitations of all current state-of-practice and state-of-the-art in situ devices (DeJong et al. 2004). In recent years, full-flow penetrometers have shown to have the potential to measure undrained and remolded strength directly, quickly, and accurately, thereby solving amajor technical obstacle in geohazard characterization. Translation of full-flow penetrometers from potential to realization for characterization of offshore sediments is not trivial. However, progress has been made internationally (COFS and NGI) and at UMass Amherst, and the collaborative scope of work contained in this proposal has the potential to result in internationally standardized probe designs, testing methodology, and data analysis and interpretation. The full-flow research scope for this project will focus on (1) practical issues regarding development of international specifications that would enable consistent and reliable implementation by engineers at any potential geohazard site in the world and (2) phenomenological issues regarding testing specifications and data analysis and interpretation. Practical issues to be addressed include design of a mandrel with a temperature compensated, moment insensitive load cell and a pore pressure module, probe compatibility with offshore drilling pipe, procedures required for remoulded strength determination, penetration rate, and framework for initial analysis factors and site-specific factor calibration. Much of the practical issues are integrated with soil behavior phenomena and properties including: strain-rate effects (viscosity and partial consolidation), sensitivity, stratigraphic and stress anisotropy, strain-softening rate, and soil type. These series of issues will be investigated in an integrated collaborative research program that will use well characterized international test sites in the US and Canada as well as sites managed by NGI (Onsøy, Norway) and COFS-UWA (Burswood, Australia). With baseline, full-flow investigations (by UMass Amherst) and extensive laboratory investigations already performed at these sites, the background research is completed, and the potential and ability to research the above issues is established.
