Page 106 - Analysis and Design of Energy Geostructures

78 Analysis and Design of Energy Geostructures

Figure 3.4 Sketch of the typical, primary component of conduction heat transfer in a geomaterial.

Figure 3.5 Typical relationship for an unfrozen (A) coarse-grained soil and (B) fine-grained soil.
Redrawn after Brandl, H., 2006. Energy foundations and other thermo-active ground structures.
Geotechnique 56 (2), 81 122.

between dry density and water content for coarse- and fine-grained soils is pre-
sented in Fig. 3.5 with reference to the data presented by Brandl (2006).
4. In addition to the influence of dry density on the number of small pores and con-
tact points, the gradation of a soil (e.g. coarse-grained soil) plays also a major role
in the variation of thermal conductivity. In fact the number of small pores and
contact points between grains increases with the more diverse granulometric com-
position of the soil. Therefore the more well-graded soils are, the higher the ther-
mal conductivity is. This phenomenon finds a comparable influence with respect
to the features of the mix design proportioning in concrete.
The influence of all of the aforementioned variables should be considered
when estimating the thermal conductivity of soil, rock and concrete in the analysis