# Thermal conductivity of soil

Soil thermal conductivity has been found to be a function of dry density, saturation, moisture content, mineralogy, temperature, particle size/shape/arrangement, and the volumetric proportions of solid, liquid, and air phases. A number of empirical relationships have been developed to estimate thermal conductivity based on these parameters. For a typical unfrozen silt-clay soil, the Kersten correlation [M.S. Kersten, 1949] may be used. The Kersten correlation was was based on the data for five soils and is valid for moisture contents of ≤7 %.

The table lists the thermal conductivities of typical soils surrounding pipelines. Although the thermal conductivity of onshore soils has been extensively investigated, until recently there has been little published thermal conductivity data for deepwater soil. Many deepwater offshore sediments are formed with predominantly silt- and clay-sized particles, because sand-sized particles are rarely transported this far from shore. Hence, convective heat loss is limited in these soils, and the majority of heat transfer is due to conduction [T.A. Newson et al., 2002].

Measurements of thermal conductivity for deepwater soils from the Gulf of Mexico [MARSCO, 1999] have shown values in the range of 0.7 to 1.3 W/(m.K), which is lower than that previously published for general soils and is approaching that of still seawater, 0.65 W/(m$K). This is a reflection of the very high moisture content of many offshore soils, where liquidity indices well in excess of unity can exist and which are rarely found onshore. Although site-specific data are needed for the detailed design most deepwater clay is fairly consistent. Figure 14-3 shows sample thermal conductivity test results for subsea soils worldwide. The sample results prove that most deepwater soils have similar characteristics. "When min/max values were given, the mean value was calculated for the nominal value. Symbol$k_{4}$Unit W/(m.K) Formulae $\frac{1}{\rho_{4}}$inverse of thermal resistivity$10^{\frac{d_{soil}}{100}} \left(0.9 \ln{\left(2100 \nu_{soil} \right)} - 0.2\right)$Kersten correlation Related$d_{soil}$Soil dry density [kg/m$^3$]$\nu_{soil}\rho_{4}$Used in$\mathrm{Bi}_{g}\mathrm{Bi}_{p}D_{soil}e_{limit}e_{soil}h_{buried}h_{ground}h_{soil}R_{q22}R_{q24}R_{q32}R_{q34}\$
Choices
IdMaterial

min
W/(m.K)
nom

max
11Peat (dry)0.17
12Peat (wet)0.54
13Peat (icy)1.89
21Sand soil (dry)0.430.560.69
22Sand soil (moist)0.870.9551.04
23Sand soil (soaked)1.92.162.42
31Clay soil (dry)0.350.4350.52
32Clay soil (moist)0.690.780.87
33Clay soil (wet)1.041.31.56
34Clay soil (frozen)2.51
41Gravel0.91.0751.25
42Gravel (sandy)2.51
51Limestone1.3
52Sandstone1.631.8852.08