Thermal conductivity of loose urban soils

Thermal conductivity of some loose urban soils in Yekaterinburg has been studied using the needle probe method. The studied samples include weathering crusts of granitic and ultramafic rocks, quartz sand and crushed piezoelectric quartz. Humidity and granulometric composition have also been studied. An increase in humidity from 2–3% to 20–25% leads to an increase in thermal conductivity from 0.15–0.3 W m^–1 K^–1 to 1.2–2.0 W m^–1 K^–1. Most samples are characterized by an “S”-shaped dependence of thermal conductivity on humidity, including an initial section of slow growth in thermal conductivity, a section of a faster growth, and a flattening of the dependence as it approaches maximum saturation. For the analytical description of experimental data, the percolation-based effective medium approximation (P-EMA) was used. The approximation error was 0.08–0.26 W m^–1 K^–1. The “critical humidity” parameter in the P-EMA approximation determines the position of curve inflection. It has been established that the critical humidity increases with the growth of the finest fraction content, i.e., clay and silty loam. Data on the thermal conductivity of loose urban soils can be used in calculating heat exchange on urban surfaces, for example, in urban heat island studies.