A critical soil moisture condition affecting buried transmission cables

Experimentation in an idealized soil showed a critical moisture content of approximately 4 percent by weight separated two distinctly different phenomena whereby heat is dissipated from buried heat sources. Above this moisture content relatively large quantities of heat per lineal foot are dissipated apparently by a circulation phenomenon. Below this content the soil rapidly dries out, materially decreasing the quantity of heat that can be dissipated. The latter may explain the so-called “runaway condition” observed with buried transmission cables.

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[2]  W. O. Smith.  Thermal transfer of moisture in soils , 1943 .

[3]  J. H. Neher,et al.  Residential heat pump experiments in Philadelphia - Earth as a heat source , 1952, Transactions of the American Institute of Electrical Engineers, Part II: Applications and Industry.