Long-term geoelectrical monitoring of landslides in natural and engineered slopes

Abstract

Developments in time-lapse electrical resistivity tomography (ERT) technology are transforming our ability to monitor the subsurface due to purpose-built monitoring instruments, advances in automation and modeling, and the resulting improvements in spatial and temporal resolution. We describe the development of a novel ERT-based remote monitoring system called PRIME that integrates new low-power measurement instrumentation with data delivery, automated data processing and image generation, and web-based information delivery. Due to the sensitivity of ERT to hydrologic processes in the near surface, we focus on the application of PRIME for moisture-driven landslide monitoring. Case examples are considered of landslides in engineered and natural slopes, including those impacting geotechnical assets in rail and highways, where slope hydrology is seen to be controlled by lithology, vegetation, fissuring, and drainage structures. We conclude by taking a forward look at emerging developments in ERT monitoring relating to hardware, software and modeling, and applications.

Variations in Bedrock and Vegetation Cover Modulate Subsurface Water Flow Dynamics of a Mountainous Hillslope

“…The ERT monitoring profile comprises 112 electrodes, with 3 m spacing between electrodes 1 and 49 (0–144 m on the steep, upper part [west] of the profile) and 1.5 m spacing from electrode 50 to the end (at the lower, eastern part of the profile, Figure 2). Data were acquired using a solar‐powered, 10 W PRIME ERT monitoring system (Chambers et al., 2022), measuring dipole‐dipole measurements with dipole lengths n of 1–7 electrode spacings, and dipole spacings a of 1 to 7 n . The survey protocol comprised a total of 4,446 electrical resistance measurements with a full set of reciprocal measurements to estimate the measurements errors.…”

Developing a novel geophysical tool to investigate the influence of vegetation on slope stability

“…To better interpret PRIME resistivity models of soil columns, further analysis of the relationship between moisture content and electrical resistivity is required (Holmes et al, 2022). A modified HYPROP2 is used in combination with the soil column experiments (Figure 7).…”

“…Therefore, it is possible to develop a quantitative relationship between these two parameters using a modified HYPROP2 system. This method was developed by Holmes et al (2022), enabling resistivity to be measured in tandem with soil suction and moisture content. Non-vegetated samples are tested at maximum dry density.…”

“…Results of the electrical resistivity-moisture content relationship are shown in Figure 8 for the Amended Topsoil fitted with the Waxman-Smits model, labelled pGMC (Waxman and Smits, 1968). The Waxman-Smits models were fitted to the data to convert electrical resistivity to gravimetric moisture content (Holmes et al, 2022). The relationship demonstrates a clear decrease in resistivity as moisture content increases.…”

“…Since the PRIME system was developed, it has been deployed in regions of slope instability, including for monitoring engineered slopes (e.g. Holmes et al, 2022). However, the PRIME system has not been applied in small-scale laboratory experiments.…”