In the Norwegian Sea and in many other extreme northern or southern latitude offshore areas, the temperature at the seabed in deep-water locations is continuously around 0 °C with the salt content of the pore fluid allowing the soil to remain unfrozen. The design of offshore facilities in these regions is generally governed by cases involving large lateral loads from waves or floating ice where the weak surficial soils become critical components. A precise estimate of soil strength and consolidation properties that avoids unnecessary conservatism can result in substantial construction and installation savings.
Previous work has shown a significant effect of increasing preconsolidation pressure and increasing undrained shear strength with decreasing temperature for clay soils. Previous work has not, however, been performed on samples from cold temperature environments that have been maintained at cold in situ temperatures during sampling, storage and testing. Previous work indicates that allowing samples to warm to room temperature and then recooling to cold in situ temperatures may result in an overestimation of undrained shear strength and preconsolidation pressure.
This project will compare the effect of temperature on laboratory strength and consolidation properties for samples taken from cold temperature environments that have been maintained at cold in situ temperature during sampling, storage and testing to those that have been stored at room temperature and then tested at both cold in situ temperature and room temperature. Two clays of different plasticity indices will be evaluated.
This work will be done in collaboration with the Norwegian Geotechnical Institute, Oslo Norway, and has the potential to impact industry through reduced construction and installation costs by recognizing the effects of cold temperature on strength and consolidation properties. In addition, results from this project have the potential to impact engineering practice through sampling, handling, storage and testing practices that can account for the effect of cold temperature on soft clay properties.
The design of offshore facilities is generally governed by cases involving large lateral loads from waves or floating ice where the weak surficial soils become critical components. A precise estimate of soil strength that avoids unnecessary conservatism can result in substantial construction and installation savings. In regions where the water depth is great or in northern cold climates, the temperature at the seabed can be near zero degrees Celsius. The research performed in this project has shown that the strength of soft marine clays is approximately 30 % greater when tested at the same cold seabed temperature as compared to testing at room temperature, as is conventionally done. This research has impacted industry, engineering practice and education. The research was done cooperatively with the Norwegian Geotechnical Institute (NGI), Oslo, Norway. A graduate student was funded by the project and assisted with the laboratory tests, analysis and reporting. This student spent 4 months at NGI where he assisted with the research, prepared reports and engaged in everyday engineering activities at the institute. The student found this to be both a valuable professional and cultural experience. Students from two graduate courses at MSU( Advanced Soil Mechanics and Applied Geotechnical Engineering) participated in this project through classroom and laboratory exercises using the tests and data from this project. Results from this research has the potential to substantially reduce industry construction and installation costs for offshore projects by the use of higher strength and improved consolidation properties that are reflective of actual cold in situ conditions. Engineering practice has the potential to be impacted by the manner in which samples from cold temperature sites are handled, stored, transported and tested. In particular, this research shows the need for maintaining cold temperatures during the testing operations. Industry is currently examining these results in preparation for implementation and altering routine practices.
