Theory and practice of soil densification

THE THERMAL RESISTIVITY of soils is an important factor in the economy of systems of buried electric power cables. This resistivity is a function of the volume fractions of the solid, liquid, and gaseous phases of which soils are normally composed, and of their structural arrangement. Inasmuch as the solid phases usually possess lower thermal resistivities than the liquid and gaseous phases and, because the latter are greatly affected by external factors such as weather and topography and, hence, are subject to cyclic variations, the volume proportion and the structural arrangement of the solid soil constituents determine the maximum theoretical thermal resistivity of a soil. The dry densities of soils are often used instead of the volume proportions of solids. An increase in dry density by one pound per cubic foot results in an average decrease of thermal resistivity of 3 per cent. Soil systems, as found in nature or as obtained by normal backfilling practices, are usually neither at their most loose nor at their densest possible state. Between these two states, there is normally a difference of about 36 pounds with the natural state often having a density of about 12 pounds above the most loose. This indicates the potentialities of decreasing the thermal resistance of soils by means of better and more appropriate compaction methods.