Fire and Ice: Innovative Applications of Deep Foundations

Alternative types of deep foundations have been designed and are under construction at Denali and Yellowstone National Parks (NPs) in the United States. At Yellowstone NP, the design mitigates hot temperatures, gases, and caustic groundwater across the Yellowstone River in a valley bottom. At Denali NP, the design mitigates degrading permafrost and an advancing rock glacier on a steep mountain slope. The designs are different in almost every way except that they show the versatility and value of drilled foundation elements. The different foundation conditions that must be dealt with are the result of past decisions and they exemplify the sentiment that the good sites are already taken. Each of these is a major bridge project where the alternatives to building at these locations had severe consequences, and the avoidance of these consequences is what drove the innovation. At Yellowstone NP, large diameter drilled shafts, with innovative casings, were used to reduce the number and depth of penetrations above a hydrothermal resource and to minimize the surface area exposed to the environment. At Denali NP, micropiles and tiedown anchors were used in surprising ways to provide a reinforced rock foundation capable of supporting construction and long-term loads, including the continued evacuation by the rock glacier. Thermosiphons were added alongside these elements to keep ice in an abutment frozen for the bridge service life and to mitigate the effects of changing climate.