Water Migration Impacts on Thermal Resistivity Testing Procedures

Abstract

This study investigated water redistribution during measurement of the thermal dry-out curve (i.e., soil thermal resistivity ρT versus volumetric water content θ). Although there is not a standard method for measuring the ρT–θ relationship, curves are typically generated with incremental ρT measurements as a specimen is dried. However, drying within a specimen may not be uniform, even in a controlled, low-temperature drying environment. In this study, ρT and θ were measured at the top, middle, and bottom of remolded cylindrical soil specimens of a range of soil types after staged drying in a low-temperature oven. Water distribution was highly varied; for example, tests on silty sand revealed θ values up to nine times greater at the bottom than at the top of the specimen, and spatial variations in θ erroneously affect measured values of ρT. Numerical models validated water migration within soil specimens during staged drying. The results indicate a need for modification of the standard thermal resistivity testing procedure to account for variations in water content across a specimen and along the sensor length during drying.