The thermal resistivity of the soil has a significant impact on cable ampacity of buried cables, especially when directly buried without backfill. The lower the thermal resistivity, the higher the cable ampacity for the same conductor temperature $\theta_c$.
If the thermal resistivity of soil is unknown, the values from the reference operating conditions in IEC 60287-3-1 are recommended. Or else, the IEEE Standard 442 provides values for some materials and a paper by O.E. Gouda from 2010 lists values for some tested type of soils.
The table lists the thermal resistivities calculated from the thermal conductivities of typical soils surrounding pipelines as given in the Subsea Engineering Handbook by Yong Bai and Qiang Bai, 2012.
|Sand soil (dry)||2.326||1.786||1.449|
|Sand soil (moist)||1.149||1.047||0.962|
|Sand soil (soaked)||0.526||0.463||0.413|
|Clay soil (dry)||2.857||0.299||1.923|
|Clay soil (moist)||1.449||1.282||1.149|
|Clay soil (wet)||0.962||0.769||0.641|
|Clay soil (frozen)||0.938|