|Way, Thomas - Tom|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/5/2009
Publication Date: 8/15/2009
Citation: Shoop, S., Countermarsh, B., Diemand, D., Way, T.R. 2009. Using soil stress state transducers in freezing ground. In: Proceedings of the 14th conference on Cold Regions Engineering, August 30 - September 2, 2009, Duluth, Minnesota. p. 562-571. Interpretive Summary: Vehicle traffic on soil typically causes the soil to compact and deform as the soil aggregates and particles move relative to one another. Frozen soil has greater strength than unfrozen soil, but little information was available about effects of vehicle traffic on mechanical stresses in frozen soil. Stress state transducers for soil, which are sensors that measure mechanical stresses in soil, were used for determining stresses in unfrozen soil, in soil in which an unfrozen layer was beneath the surface frozen layer, and in frozen soil. Traffic was applied to the soil by a vehicle equipped with pneumatic tires. The transducers functioned very well in frozen ground. Magnitudes of the soil stresses diminished as the ground above the sensors froze and decreased further as the frost enveloped the entire sensor. This research shows that soil compaction, which typically increases as stresses in soil increase, may be reduced when vehicles traffic frozen soil, compared to unfrozen soil.
Technical Abstract: Three instrumented test sections of sand, silt and clay, were constructed to monitor the impact of frost layers on vehicle-induced stresses and to assess the performance of the sensors used to measure such stresses. One of the instruments used to measure in-situ stress is the soil Stress State Transducer (SST), which was installed at 12.7 cm depth within each of the test soils. The SST was developed by the USDA Agricultural Research Service, National Soil Dynamics Laboratory and the Auburn University Department of Agricultural Engineering, and has been used in many studies on vehicle induced stresses in agricultural soils, but not previously in freezing soil. Each SST consists of six semiconductor pressure transducers installed in a small sphere. Soil displacements, temperature and moisture and strength profiles were also monitored. Trafficking of the test sections was performed at frost depths ranging from zero to over 50 cm. The SSTs functioned very well in frozen ground. The signals clearly showed the passage and sometimes the bow wave in front of each tire, and then the large vertical pressure spike as each tire passes over the sensor. The stress magnitudes diminish as the ground freezes above the sensors and then decrease further as the frost envelops the entire sensor.