Monitoring Rock-freezing Experiments in the Laboratory with Capacitive Resistivity Imaging

Abstract

We explore a new technology concept for the non-invasive volumetric imaging and routine temporal monitoring of permafrost-affected bedrock. Capacitive Resistivity Imaging (CRI), a technique based upon a low-frequency, capacitively-coupled measurement approach is applied to laboratory experiments simulating permafrost growth, persistence and thaw in bedrock with the aim of emulating Electrical Resistivity Tomography (ERT) methodology, but without the need for galvanic contact on frozen rocks. Experimental results using conventional ERT highlight the practical problems with maintaining adequate galvanic contact between steel electrodes and rock samples that are subjected to multiple freeze-thaw cycles. Multi-sensor CRI measurements on permafrost rock samples using newly developed CRI instrumentation demonstrate the feasibility of laboratory-scale 3D/4D imaging with capacitively coupled sensors. The results suggest that the CRI technique can usefully complement the characterisation and monitoring of permafrost rock samples. We expect that the methodology will allow us to obtain calibrated images of the temperature distribution in the sample. Controlled long-term permafrost physical modelling experiments are currently underway, monitored with CRI and ERT. Field installations of the new capacitive sensor technology are envisaged.