Application of a nondestructive method to evaluate the active layer in a cold region

Abstract

To provide a safe transportation system in an extremely cold region, evaluation needs to be conducted of the thickness and the volumetric water content of the active layer, as they significantly affect frost heave. The objective of this study was to evaluate the dielectric constant ( κ ) of the active layer using ground-penetrating radar (GPR) and a dynamic cone penetrometer (DCP); this evaluation was then used to estimate the thickness and the volumetric water content of the active layer. A field located in midwest Alaska was selected as the study site. A GPR survey and two DCP tests were conducted on the surface of the ground, and the ground temperature was measured. From the GPR survey, travel times of the electromagnetic wave in the active layer were obtained. In addition, the thickness of the active layer was determined by using the dynamic cone penetration index (DCPI) and ground temperature. By using the travel time and travel distance of the electromagnetic wave in the active layer, dielectric constants were calculated as 26.3 and 26.4 for two DCP points. From the mean dielectric constant, the volumetric water content was estimated to be 40%~43%, and the thickness of the active layer was evaluated along the GPR survey line. The spatial-scaled GPR image showed that the thickness of the active layer varied from 520 mm to 700 mm due to the presence of a puddle, which accelerated the heat exchange. The results show that evaluation of the dielectric constant using the GPR survey and the DCP test can be effectively used to estimate the thickness and the volumetric water content of the active layer.