THE EFFECT OF GRAIN-SIZE ON THERMAL-CONDUCTIVITY OF QUARTZ SANDS AND SILTS

Synthetic samples of different grain size fractions of quartz were pre pared and the thermal conductivities measured with a divided bar appar atus. The measurements were carried out on dried and water-saturated s amples both perpendicular and parallel to the main stress direction du ring compaction of the samples. A clear correlation was observed betwe en the porosity and the measured thermal conductivities. For water-sat urated samples the thermal conductivity decreases more with increasing porosity than for ideal isotropic material as predicted by the geomet ric mean model. A clear positive correlation was also found between th e thermal conductivity and the grain sizes of the samples. When the ex pected effect of porosity on the thermal conductivity was excluded, a linear correlation between the logarithm of the grain size and the mea sured thermal conductivities of the water-saturated samples was found. An anisotropy effect (a=k(parallel to)/k(perpendicular to)) in therma l conductivity was observed for the samples, being most prominent for the coarsest ones. The measured anisotropy is assumed to be mainly due to the thermal anisotropic nature of the quartz crystal.