Thaw Penetration in Frozen Ground Subjected to Hydronic Heating

Abstract

To facilitate excavation and foundation work in seasonally freezing or permafrost regions, the frozen soil must be thawed, either by natural (solar) thawing, or by artificial thawing where an auxiliary heat source is utilized to accelerate the process. In this paper, the process of rapid thawing of frozen ground subject to hydronic heating is studied. In particular, the performance characteristics of the method is evaluated through full-scale thawing experiments performed on three types of homogenous, initially frozen soils. The results from two separate experiments, carried out during the winter of 2011 and 2012, were compared. The corresponding soil temperature increase, phase change, and variation in water content for each type of soil were monitored. The results from both winter seasons show similar trends, with comparable and considerable higher thaw rates for gravelly sand (∼3.5 days/m∼3.5 days/m) and silty sand (∼4 days/m∼4 days/m) compared with crushed gravel (∼11.5 days/m∼11.5 days/m). Furthermore, thaw rates compiled from thermistor strings in tubes embedded in the ground are overestimated compared with similar temperature readings based on thermocouples in direct contact with the soil.