Thermal Conductivity of Consolidating Offshore Clayey Backfill

Pipelines that transmit untreated products are prone to waxing and hydrate formation unless the fluid is kept above certain temperatures. Since bare pipe can have relatively high thermal conductivity, pipes can be buried to utilise the thermal properties of the surrounding soil. However, the thermal conductivity of clayey offshore trench backfill as it consolidates is poorly understood. This paper describes a series of laboratory tests on offshore clayey sediments to investigate the coupled compressibility and thermal conductivity behaviour. The compressibility behaviour of the soil samples was characterised using a specially designed oedometer apparatus. Measurements of thermal conductivity were taken periodically during the loading sequence. This data was used to model the behaviour of the backfill in a hypothetical jetted offshore trench using finite element analysis. The laboratory testing indicated that the stress-strain behaviour of the undisturbed and reconstituted material seems to be typical of similar onshore clayey soils. The data showed lower thermal conductivities for both the undisturbed and reconstituted soils than have previously been reported by industry for these types of soil. The results have provided extremely useful data on the fundamental behaviour of offshore clayey sediments and have given confidence in predictions of the coupled consolidation and thermal conductivity behaviour of jetted offshore soils using finite element analysis.