145-12 Innovative Approaches to Soil Swell Measurement in Landslide Regions Using UAS Photogrammetry

Session: Dynamics of Natural and Built Environments (Posters)

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Abstract:

Landslides present significant hazards to public safety and are primary agents of landscape change. However, mechanisms restraining landslide deformation remain incompletely understood, often rendering forecasting of landslide timing and speed intractable. The northern California Coast Range hosts thousands of slowly and episodically moving landslides underlain by Franciscan Complex mélange. A 2018 study of one landslide along Kekawaka Creek, California, found that soil swelling contributed to nearly 10% of the slide’s shear resistance and delayed onset of motion until 5 months after peak saturation levels. The contribution of variable soil swell pressure was thus identified as a mechanism for restraining motion in clay-rich landslides. Here, we attempt to expand upon that work using structure from motion (SfM) products derived from unoccupied aerial system (UAS) photogrammetry surveys to analyze soil swell distribution across a broad region (~10 sq km), including the original slide area and three additional slow-moving landslides nearby.

Point clouds were generated from three flight campaigns in February 2024, August 2024, and August 2025, with February and August representing epochs of maximum swell and shrink, respectively. Point cloud co-alignment was performed using iterative closest point (ICP) transformations on subsampled reference areas identified as stable. Change detection of co-aligned point clouds was then quantified using the multiscale model-to-model cloud comparison (M3C2) algorithm. Approximate ground truthing for the vertical component of soil swell magnitude was conducted using three downhole extensometers on three of the landslide surfaces, and soil swell pressures were measured using total stress cells at eight locations. Groundwater pressure heads were measured from seven monitoring stations distributed across the study area. Soil swell of around 2 cm was measured in downhole extensometers anchored ~2-3 m below the ground surface, while swell pressures as high as 22 kPa were observed from ~1.5 m below ground. Point cloud elevation difference values proximal to those locations were in general agreement, suggesting this technique provides sufficient precision to be a viable means of quantifying soil surface shrink-swell magnitude. Shrink-swell magnitude varied across the region surveyed, likely reflective of high compositional variability of the mélange, variable moisture conditions and possibly a topographic dependance. Ongoing work consists of characterization of shrink-swell variability and its impact on landslide dynamics.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8820

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