The Science

Predictive understandings of soil biogeochemical processes and slope stability are limited partly by the inability to observe subsurface geomechanical dynamics and their drivers at a relevant number of locations. Technological solutions are needed for long-term, multiscale monitoring of soil deformation. However, current instruments are often costly, require a complex installation process and/or data processing schemes, or have poor resolution. Here, scientists present a novel sensing solution that uses linear arrays of temperature sensors and accelerometers. From an electromechanical perspective, a novel board-to-board connection method was developed that enables narrow, semi-flexible sensor arrays and a streamlined assembly process.

The Impact

The designed sensor probe consists of a thin, semi-flexible tube that contains accelerometer and temperature sensors mounted on multiple cascaded boards with novel board-to-board connectors. Experiments performed with probes up to 1.8 m long demonstrated high spatial resolution and accuracy, long-term connector stability, and mechanical flexibility. In contrast to alternative solutions, this approach measures depth-resolved deformation, which can inform about shallow sliding surfaces. This low-cost technology enables scientists to acquire data with an unprecedented resolution through densely distributed sensor networks. It is an essential tool for understanding landslide behavior, as well as various cryospheric, hydro-biogeochemical, and geomorphological processes that impact water and carbon fluxes.

Summary

Scientists developed a novel, low-power, flexible sensor array for monitoring soil deformation and temperature in slopes with shallow instabilities. In contrast with conventional approaches, the presented solution is low-cost, lightweight, robust, and easy to install, enabling multi-scale deployments in densely distributed, wirelessly connected configurations. The electronic design contains a configuration of cascaded temperature sensors and accelerometers, compatible with an existing 2×AA battery-powered data logger. To meet the mechanical requirements of the sensor probe, a novel, solderless board-to-board connection method was developed. This method does not require any components and enables extremely thin, semiflexible probes of adjustable length. An extensive study of the contact resistance demonstrated long-term stability, even under bending (radius up to 200 mm). The entire probe assembly shows significant deformation under small (<1 N) forces, which demonstrates that the probe’s deformation is representative for soil movement. An assessment of the measurement accuracy shows that deformation measurements under a constant temperature have a 95% confidence interval of ±0.73 mm/m. A set of probes in a permafrost environment showed continuous soil displacement at a rate of 2 mm/day, starting from the interface between frozen and unfrozen soil. This represents a first step in quantifying soil movements and their controls in permafrost environments, which is critical to improve our understanding of carbon cycle.

Principal Investigator

Stijn Wielandt
Lawrence Berkeley National Laboratory
stijnwielandt@lbl.gov

Co-Principal Investigator

Baptiste Dafflon
Lawrence Berkeley National Laboratory
bdafflon@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was supported by the Biological and Environmental Research (BER) Program within the U.S. Department of Energy’s (DOE) Office of Science to Lawrence Berkeley National Laboratory (LBNL). It is part of the Next-Generation Ecosystem Experiments—Arctic (NGEE-Arctic) project and LBNL’s Laboratory Directed Research and Development (LDRD) Program under DOE Contract No. DE-AC02-05CH11231.

References