Thermal resistivity and moisture migration of soil and cable trench backfill

Abstract

There are many innovative applications of thermal properties of soil and backfill, such as geothermal cooling and heating systems, backfilling of high-voltage cable, etc., being developed. Therefore, there is a need to develop a better understanding of the thermal behavior of soil and backfill. The thermal resistivity and moisture migration behavior of a number of soils including those frequently used for high-voltage cable backfill have been studied in laboratory-scale and field-scale experiments, so as to evaluate their suitability as a backfill material. Thermal resistivity of small soil specimens was measured in the laboratory using a probe. Moreover, compaction mold thermal moisture migration tests were carried out for larger specimens in the laboratory. A full-scale field test was performed by means of a simulated cable installation. The results indicate in general that well-graded granular materials have the most desirable thermal behavior, and poorly graded soils (especially granular and coarse soils) have the least desirable thermal behavior, in terms of thermal resistivity and moisture migration driven by a thermal gradient.