Thermal Conductivity of Sand with Fines

Through a series of more than 100 laboratory-controlled tests that employed a specially designed soil thermal conductivity measurement apparatus, this work quantifies the variations in thermal conductivity k for dry sand with changes in type and percentage of fines Fp and relative density DR of sand–fines mixtures. Six different types of fines (kaolin, sodium bentonite, calcium bentonite, marine silt, red soil, and black cotton soil) were used (one at a time) to prepare dry sand–fines mixtures at four distinct values of DR (40%, 60%, 75%, and 90%) and with Fp varying between 0% and 20%. Results demonstrate that mineralogical composition and specific surface area of fine particles present in a predominantly sand deposit greatly influence both transient- and steady-state values of k (ktr and kst, respectively). For fixed values of DR and Fp, ktr and kst values for sand–fines mixtures with different types of fines varied up to 60% and 26%, respectively. In the presence of fines up to 20%, comparison of measured k values with those predicted using a few existing empirical models identified the need for revisions in model constants to restrict the average values of model bias factor to close to unity. Furthermore, a comparative assessment of effective thermal conductivity predictions using three idealized mathematical models revealed that the geometric mean model (GMM) can successfully (with a ±15% deviation) account for the mineralogical constituents and percentage of fines in estimation of k for sand with fines.