The development of four dimensional electrical resistivity tomography for laboratory-scale imaging of soil moisture dynamics

Abstract

This study considers the combination of a novel geophysical monitoring system and geotechnical point sensors for use in controlled laboratory conditions to visualise soil moisture dynamics in different engineered soils. The geophysical monitoring system, referred to here as PRIME (Proactive Infrastructure Monitoring and Evaluation system), uses electrical resistivity tomography (ERT) technology to non-invasively image subsurface moisture-driven processes. The PRIME system and point sensor arrays have been developed for near real-time data acquisition of transient soil moisture conditions in a suite of soil column experiments. This research aims to provide new tools and approaches to further our understanding of soil moisture movement to better assess shallow geotechnical assets by addressing the challenges associated with designing integrated geophysical-geotechnical laboratory-scale monitoring experiments. A total of nine soil column experiments were carried out in this research. Soil moisture content, grain size and density were changed throughout the study to gauge the proficiency of time-lapse ERT for various soils. Nine soil column experiments were conducted to evaluate the effectiveness of time-lapse ERT in various soil compositions, assessing changes in moisture content, grain size, and density. One of the main challenges associated with integrating ERT in a soil column setup is the prevalence of artefacts in the time-lapse imaging. These artefacts, presenting as high or low electrical resistivity contrasts, can be a common feature in ERT surveys and are known to reduce the accuracy of the inversion. This study takes steps to reduce the tendency of artefacts in the results by systematically identifying the source of such modelling errors and adapting the 4D ERT integrated soil column design accordingly. Alongside plotting the electrical resistivity of transient soil moisture conditions in the column experiments, petrophysical relationships derived from the ERT soil columns focus on understanding the link between soil moisture content, electrical resistivity, and suction. These relationships are crucial for improving the interpretation of time-lapse ERT data and enhancing the accuracy of soil moisture monitoring in laboratory and field applications. Findings demonstrate the potential of integrating ERT with geotechnical monitoring systems to advance understanding of soil moisture movement, with applications in geotechnical asset management and environmental engineering.