Real-Time In Situ Monitoring of Frost Depth, Seasonal Frost Heave, and Moisture in Railway Track Structures

In the winters of 2010 and 2011, several hundred kilometers of the Finnish railway network had decreased speed limits due to uneven rail caused by frost problems. To study the causes more closely, Tampere University of Technology has developed a monitoring system for measuring the frost depth and frost heave of railway track structures at selected sites across a range of different climatic zones in Finland. The system includes measuring the temperature using analog semiconductor-type temperature sensors placed on 100- to 500-mm intervals down to a depth of 3 m. Linear displacement transducers installed on both ends of instrumented sleepers are used for measuring frost heave and/or settlement of the sleepers. The moisture content in different layers is measured with dielectric-type moisture sensors. Two kinds of data loggers are used for data collection, with data being transferred from the field sites via a wireless network connection. The first monitoring sites have collected and sent data since 2008 with minimum maintenance. The final purpose of the monitoring is to enable modeling of frost heave in the field based on material properties determined in the laboratory and conditions (moisture, temperature) in the field.