Evaluating Automated MEMS-Based In-Place Inclinometers in Cold Regions

Inclinometer probes are used to measure ground movement. While an industry standard, this technology has drawbacks, including costly trips for manual measurements, operator error, and limited measurements due to casing deformation. Relatively new to the industry, MEMS-based in-place inclinometers (M-IPIs) are composed of a series of MEMS accelerometer segments separated variously by flexible joints or field-connection systems, and encased in watertight housing. M-IPIs provide nearly continuous ground movement measurements without frequent field trips, accommodate greater ground movement due to their flexibility, and may contain temperature sensors, useful for frozen ground applications. Since M-IPIs have not been evaluated fully for use in cold regions, two M-IPIs from different manufacturers were installed in an area of known slope instability within permafrost in south-central Alaska. Each M-IPI was evaluated for ease of installation and subsequent retrieval, durability, and functionality in frozen ground. M-IPI ground movement data and temperature measurements were compared to those obtained using an inclinometer probe and thermistor string, respectively. All instruments indicate ground movement at a depth of approximately 16.8 m (55 ft). Measurements from both devices compare well to those from the inclinometer probe, with measurements of the same casing differing less than 1.8 mm (6.9x10^-2 in.) and measurements of two adjacent casings differing less than 3.8 mm (0.15 in.). Temperature data analysis indicates that the M-IPI devices measured temperatures within ~0.2°C (0.4°F) of those recorded by the thermistor string. If used to measure both ground movement and temperature in frozen ground, the M-IPI temperature sensors should be calibrated.