Using a Multisegment Time Domain Reflectometry Probe to Determine Frost Depth in Pavement Systems

Determining frost depth below the pavement is important for timely implementation of winter and spring load limits. Unfortunately, existing instruments such as resistivity probes, frost tubes, and moisture blocks are limited in terms of both data acquisition (automated and continuous measurements) and data interpretation. Consequently, a delay between data collection, interpretation, and dissemination of information occurs. A laboratory study was conducted by the Minnesota Department of Transportation to investigate the use of the Moisture Point probe as an instrument for locating the depth to the freezing front. The Moisture Point probe combines time domain reflectometry with remote diodeswitching to provide a profile of aggregate base and subgrade dielectric properties. From this, the frost depth can be estimated. The Moisture Point probe works well in locating the frost depth, and it improves the ability to successfully implement spring and winter load limits. This method also provides the opportunity to validate air temperature–based models that are currently used to set spring and winter load limits.