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New capabilities for measuring and monitoring are needed to improve the shrink/swell hazard. A new French experimental site at Chaingy (Centre-Val de Loire) has been instrumented using extensometers at the surface and soil moisture sensors in the clay layer. Here we show by direct comparison between remote and in situ data for a period longer than three years that the vertical ground displacements are well-captured by the Multi-Temporal Synthetic Aperture Radar Interferometry (MT-InSAR) technique. In addition to the one-year period, two sub-annual periods that reflect both average ground shrinking and swelling timeframes are unraveled by a wavelet-based analysis. Moreover, we propose here to combine data from two satellite sensors, namely the surface soil moisture from the SMOS satellite with the vertical displacement from Sentinel-1A/1B. The relative phase difference between both time series for the shrinking and swelling periods is calculated for assessing the variations in terms of depth and thickness of the clay layer. An Electrical Resistivity Tomography (ERT) survey is carried out in the studied zone to validate this new method relying fully on remote sensing observations. With regard to future works, the same method coupling different satellites acquisitions may be scaled up to track the expansive clays in a larger area.

In parallel, an innovative internal erosion numerical modeling approach, based on Discrete Element-DEM and Lattice Boltzmann methods-LBM, has been developed through a partnership between the French Geological Survey (BRGM) and the Environment and Agriculture National Research Institute (IRSTEA). The upward propagation of cavities within the cover were successfully simulated. The role of different parameters (soft cover cohesion, hydraulic head, system geometry, etc.) in the sinkhole occurrence were tested by a parametric analysis.

New capabilities for measuring and monitoring are needed to prevent the shrink-swell risk caused by drought-rewetting cycles. A clayey soil in the Loire Valley at Chaingy (France) has been instrumented with two extensometers and several soil moisture sensors. Here we show by direct comparison between remote and in situ data that the vertical ground displacements due to clay expansion are well-captured by the Multi-Temporal Synthetic Aperture Radar Interferometry (MT-InSAR) technique. In addition to the one-year period, two sub-annual periods that reflect both average ground shrinking and swelling timeframes are unraveled by a wavelet-based analysis. Moreover, the relative phase difference between the vertical displacement and surface soil moisture show local variations that are interpreted in terms of depth and thickness of the clay layer, as visualized by an electrical resistivity tomography. With regard to future works, a similar treatment relying fully on remote sensing observations may be scaled up to map larger areas in order to better assess the shrink-swell risk.

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