Evaluating In-Place Inclinometer Strings in Cold Regions

AIDC project number: 309022


Margaret Darrow (UAF)

  • US Department of Transportation (RITA)
  • Alaska Department of Transportation & Public Facilities
  • Start Date: Jul 1, 2009
  • End Date: Feb 15, 2013

Project Summary

Inclinometers measure ground movement — in either a vertical or horizontal direction as appropriate — for slopes, embankments, bridge and retaining wall structures, and other applications. Current technology for vertical inclinometers relies on installing a grooved casing into a drilled test hole. Workers manually lower a two-foot-long inclinometer probe fitted with wheels down a vertical casing (or pull it through a horizontal casing). Measurements of orientation from true vertical (or horizontal) of the inclinometer at the time of measurement are recorded at specified intervals. This technology has many drawbacks. Since data acquisition requires manual measurements, workers face expensive and potentially dangerous travel. Weeks or months often pass between manual readings due to budget considerations, causing workers to merely interpolate the recorded data. Accuracy of the data collected depends on the care and skill level of the person taking measurements. The inclinometer casing has limited flexibility and can shear when excessive ground movement occurs. In addition, the inclinometer probe length limits the amount of deformation a casing can experience before readings are no longer possible. A new type of geotechnical instrumentation incorporates Micro-Electro-Mechanical Systems accelerometers, which were first used for automotive air bags. Automated in-place MEMS inclinometer strings are a series of accelerometers connected with flexible joints and encased in watertight housing, making these devices suitable to bury directly in the ground. The AIMIS are far more flexible than grooved casing and can accommodate much greater ground movement. When the installation is accompanied by a remote power supply and a telemetry link, an AIMIS can provide nearly continuous observation of ground movement without frequent field trips. AIMIS manufacturers state that these devices are reusable, as they can be removed from one installation and placed into another, resulting in further cost savings. Since the AIMIS technology is new, its use has not been fully evaluated, especially in cold regions. Although AIMIS potentially can be reused, the techniques to extract the strings are in their infancy and are problematic. New extraction techniques for use in frozen ground may need to be created and evaluated, and as with any equipment used in cold regions, the durability of AIMIS at subfreezing temperatures needs to be evaluated. The objectives of this study are threefold: to compare AIMIS against the existing methodology, to evaluate AIMIS for their versatility and accuracy in cold regions, and to test AIMIS ease of use and recoverability. AIMIS will be evaluated for applications in Interior Alaska that include monitoring creep in frozen ground and identifying and monitoring a slide shear zone. Two different AIMIS products will be compared with the existing manual method and with each other, to identify any benefits of one product over another. AIMIS will be extracted from vertical installations in order to evaluate their reusability. Based on the fieldwork and data analysis, researchers will develop a set of Best Practice Guidelines for choosing AIMIS for specific applications and for AIMIS installation, monitoring, maintenance, and retrieval. Should the AIMIS prove to be suitable for use in cold climates, transportation agencies will reduce project travel budgets and increase worker safety, and will have dependable, accurate measurements, allowing for more confidence in designs.