Monitoring critically saturated conditions for shallow landslide occurrence using electrical resistivity tomography

Abstract

Soil wetness is an important property in determining the variable disposition of hillslopes to shallow landslides. Recent studies have demonstrated the potential of in situ soil wetness information for landslide early warning. However, the spatial representativeness of in situ sensors may be affected by local heterogeneities of soil properties and hydrological processes, and their installation may be destructive. Electrical resistivity tomography (ERT) has been used in the past to estimate plot‐scale soil moisture variation and may overcome these limitations. In this study, we installed and operated an automated ERT monitoring system on a landslide‐prone hillslope in the Napf region (Switzerland). The system was operational during a period of 9 mo, and measurements were conducted at high temporal resolution and under different soil hydrological conditions. Electrical resistivity was measured along two perpendicular profile lines in Wenner–Schlumberger configuration at 0.25‐m electrode spacing. Soil saturation was calculated by the Archie's law and the parameters were fitted with colocated soil moisture sensors. Comparison of ERT‐derived soil moisture with soil wetness from in situ sensors showed a good correlation, and infiltration properties critical for landslide early warning could be reliably reproduced. Further, analysis of spatial saturation variation revealed that ERT was capable to detect heterogeneities of soil hydrological process. Under highly saturated conditions, the reliability of the saturation estimation was affected by an increased number of faulty measurements and the spatial heterogeneity of the infiltration process.

Monitoring spatiotemporal soil moisture variability in the unsaturated zone of a mixed forest using electrical resistivity tomography

“…For this purpose, Equation () according to Keller and Frischknecht (1966) was used, which was already applied in different studies (cf. Brunet et al., 2010; Chambers et al., 2014; Fan et al., 2015; Jodry et al., 2019; Wicki & Hauck, 2022). Usually, the data are corrected to a standard temperature of 25°C (Brunet et al., 2010).…”

“…To derive estimated temperature data for all depths, we used a model derived from Musy and Soutter (1991), which was already applied, for example, by Brunet et al. (2010) and Wicki and Hauck (2022). We used Equation () to estimate the soil temperature: $$$$\begin{equation} T\left(z,t\right)={T}_{\textit{mean}\left(\textit{air}\right)}+A/2e\left(-\frac{z}{d}\right)\sin \left({\it{\omega}} t+\phi -\frac{z}{d}\right) \end{equation}$$$$…”

“…We follow Hayley et al (2010), who showed that a temperature correction before inversion can lead to better results. According to Wicki & Hauck (2022), we applied the approach in which the values of apparent resistivity were directly corrected with weighted temperature fields. The temperature used for the correction at each level of apparent resistivity was calculated as a weighted average of the temperature of all overlying depth layers, with increasing weight closer to the surface.…”

“…Soil temperatures of the upper depth layers at 20, 40, and 80 cm depth are available for the entire period of measurements by the Tensiomark sensors. To derive estimated temperature data for all depths, we used a model derived from Musy and Soutter (1991), which was already applied, for example, by Brunet et al (2010) and Wicki and Hauck (2022). We used Equation (3) to estimate the soil temperature:…”

Application of Vertical Electrical Sounding for Subsurface Characterization to Determineslope Instability at Perizie, Nagaland

“…These movements are mostly due to the instability of rock masses from the slopes, whose main constituents are soil, fractured rocks, and weathered materials. [16][17][18][19][20][21][22][23] Weakness zones are those areas whose mechanical properties are considered as significantly lower compared to the surrounding rock masses. It can occur as fault zones, shear zones or weak rocks and most of these zones are the results of numerous ruptures undergoing over geological time.…”