Engineering properties of low to medium overconsolidation ratio offshore clays

Abstract

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.