Modeling and monitoring permafrost thawing in a controlled laboratory experiment

Abstract

Being able to detect thawed areas in permafrost is important as permafrost degradations may lead to weaken house and building foundations and reduction in the stability of some mountain slopes [I]. On the other hand, detecting water under frozen surfaces of planets like Mars is an important issue in planetary exploration [ 2 ] . Ground-penetrating radar (GPR) has been widely used for ground exploration in cold regions owing to the excellent penetration of radio waves in ice, snow, and frozen ground [3][6]. In addition, the liquid water content strongly influences the electric properties of a medium. Thus GPR is well suited to localize with high resolution unfrozen zones beneath and within permafrost. Prospecting for new developments in monitoring underground processes in space and time with GPR requires 4D test data sets. The large space and time scales of most geological targets like permafrost make them quite unpractical for this usage. Thus we decided to develop an experiment at the scale of the laboratory involving a medium whose electrical properties can partiaIly change under the control of the operator. In this paper, we present GPR data acquired above half a meter cube of soil frozen in a cold chamber with a heater at its bottom. In Section 11, we describe the experimental setup. In Section 111, we present the non-migrated GPR profiles acquired before and after actioning the heater and a model explaining the data. Finally, we compare in Section IV the GPR and thermocouple monitoring of the refreezing phase.