Effect of lamination and mixture on thermal conductivity of granular soil systems

Safe and reliable operation of submarine cables depends critically on the thermal properties of the surrounding soils that dictate heat dissipation efficiency and cables’ ampacity ratings. Naturally stratified or finely laminated soils are often encountered along cables’ extensive routes. While features of soil laminations are often disrupted during sample collection or cable installation, they may remain intact in large areas surrounding the cables, inducing significant variabilities in soils’ structures and states that could impact their thermal performance. This paper presents an experimental research programme into the influence of soil layering or lamination conditions on the thermal conductivity of granular soils. Measurements were taken using a customised thermal needle-based device on three binary mixtures formed by silt and sand materials of siliceous mineralogy. The findings indicate that the particle size distributions of the fines within the soil matrix - whether laminated or uniformly mixed - affect sample dry density, interparticle contact, and, consequently, the soil mixtures’ apparent thermal conductivities. Dry density was found to be the predominant factor influencing the measured thermal conductivity values, irrespective of relative fines content. Empirical correlations between normalised thermal conductivity and soil dry density are proposed to trace the thermal conductivities of dry and submerged mixtures across varying fines distribution modes. Practical implications of the research findings for submarine cable design and other geotechnical systems are also discussed.