Use of Geothermal Deep Foundations for Bridge Deicing

Winter deicing practices reduce the longevity of bridge infrastructure and make it difficult to achieve the national goal of a bridge service life of 100 years or more, which was set by SHRP 2. The vast majority of these bridges are supported on deep foundations. The goal of this study was to evaluate the concept of employing geothermal deep foundations (energy piles) to heat the bridge slab and thereby minimize or eliminate the use of deicing salt. This concept had the advantage of using required foundation elements to function also as heat exchangers with the surrounding soil, which approximated a constant temperature below a depth of 1 to 3 m (depending on the region). This paper describes a two-dimensional (2-D) finite element model used to assess the power demands to heat a typical bridge slab. Initially, the 2-D model of a conventional bridge (not incorporating the geothermal system) was validated by using a case study for a bridge in Rhode Island for which the temperature of the bridge slab was monitored for about 1 year. Once validated, the model was extended to include the effects of geothermal deep foundations for weather conditions in Philadelphia, Pennsylvania, as an example. Analyses were conducted to simulate the performance of the geothermal system with and without preheating of the bridge slab before the snow or ice formation event.