Search

This paper presents a summary of the geotechnical engineering properties of low to medium overconsolidation ratio offshore inorganic clays derived from a high quality database. These properties, such as preconsolidation stress and undrained shear strength, are required for design of most offshore infrastructure and for assessment of offshore geohazards. The database was developed through a series of Joint Industry Projects using results from offshore site investigations performed worldwide. The key feature of the database is that it only contains results obtained using good to excellent quality samples that were tested using advanced laboratory procedures such as constant rate of strain consolidation and consolidated undrained triaxial and direct simple shear. A secondary objective of the paper was to examine common empirical correlations between index tests (e.g., water content, Atterberg limits) and soil design parameters using the new database. Such empirical correlations between simple and inexpensive index tests and more costly advanced laboratory tests can serve a valuable purpose in offshore infrastructure design. This is particularly the case for preliminary design at early stages of projects where little information is known about soil properties, for small projects with limited site characterization budgets, and international projects at locations where advanced laboratory tests performed to international standards are not available. The paper describes development of the database and presents summary results and plots for undrained shear strength, in situ stress state, and consolidation and flow parameters. Results from the empirical correlations investigated are presented and the paper concludes with recommendations on use of the data and correlations in practice. The recommendations are limited to clays of low to medium overconsolidation ratio and are not applicable to highly overconsolidated and desiccated clays. While the database primarily consists of offshore clays, the correlations presented should also be applicable to terrestrial clays.

This paper describes the geology and geotechnical engineering properties of a sensitive marine clay deposit at a research site located in Newbury, Massachusetts (MA) in the northeast USA. Results from in situ testing, soil sampling, and laboratory testing are presented. The clay is locally known as Boston Blue Clay (BBC) which is a glacial marine clay that was deposited approximately 14,000 years ago in the greater Boston, MA area during retreat of the Laurentide Ice Sheet. The thickness, stress history, and soil properties of BBC can vary significantly depending on location. At the Newbury research site, the BBC deposit consists of a shallow thin desiccated crust underlain by a 12-meter thick low plasticity clay with an overconsolidation ratio ranging from 2 to 3. Sensitivity of the clay ranges from approximately 10 to 30, based on field vane and fall cone measurements. In situ testing performed at the site included seismic piezocone and field vane. Soil sampling was performed using a variety of samplers including Sherbrooke block, fixed piston thin-walled Shelby tube, and a thick-walled drive sampler. A full suite of advanced laboratory tests was performed on the various quality samples collected, which ranged from very poor (thick-walled drive sampler) to excellent (Sherbrooke block), including constant rate of strain consolidation, consolidated undrained triaxial and direct simple shear. The efficacy of the Recompression and SHANSEP procedures to mitigate sample disturbance was evaluated using results from the advanced laboratory test program. The paper presents data from these advanced tests as well as other soil classification, index, and engineering properties based on in situ measurements and laboratory test results. A synopsis of constructed facilities built on and in BBC within the greater Boston area is also presented.

This paper describes the geology and geotechnical engineering properties of the Halden silt; a 10–12 m thick deposit of fjord-marine, low plasticity clayey silt. Over the last six years, the test site has been well characterized by combining the results from a number of geophysical and in situ tools, including; electrical resistivity tomography, multi-channel analysis of surface wave surveys, cone penetration testing, dissipation testing, in situ pore pressure measurements, seismic flat dilatometer testing, field vane testing, self-boring pressure meter testing, screw plate load testing and hydraulic fracture testing. The results from these investigations assist the interpretation of layering and in situ soil properties. Soil sampling and advanced laboratory testing have provided data for interpretation of geological setting and depositional history, soil fabric, strength, stiffness and hydraulic properties. However, interpretation of the stress history, based on oedometer tests and clay-based correlations to the cone penetration test, are unreliable. They contradict the depositional history, which suggests that the soil units at the site are near normally consolidated, except for some surface weathering and desiccation. Further, undrained shear strength interpretations are complex as the in situ tests are potentially influenced by partial drainage, and conventional undrained triaxial tests do not provide a unique (peak) undrained shear strength. Despite certain interpretation challenges the paper presents important reference data to assist in the interpretation and assessment of similar silts, and provide some guidance on important geotechnical properties for projects where limited design parameters are available.