CLIENT: Western Federal Lands Highway Division

LOCATION:Yellowstone National Park, Wyoming, USA

BGC is providing geotechnical and geological engineering services for project planning and final design of a new multi-span bridge over the Yellowstone River near Tower Junction in Yellowstone National Park. The proposed signature bridge will be approximately 1,300 feet in total length with a span length of up to 400 feet in the center section, where the total height of the bridge will approach 120 feet above the river. Given the preservation objectives of the National Park Service and the historical legacy of Yellowstone National Park, the bridge planning constraints include limiting disturbance to complex terrain and sensitive environmental and wildlife habitat conditions that are critical to maintaining a positive visitor experience for several future generations. The geothermal conditions that make Yellowstone a popular place to visit also generate safety and technical challenges associated with geothermal conditions below bridge foundations where groundwater temperatures can exceed 150°F and H2S gas venting is known to exist. BGC’s work on this project includes informing initial planning decisions with geological information, geological and hydrothermal feature mapping, difficult access geotechnical investigations to characterize subsurface conditions, remote sensing for ground change measurement, slope stability analysis, foundation recommendations, and geotechnical support to contract documents.

Unique to this project and a critical aspect of the geotechnical field program was to ensure the safety of field crews in an area with a known H2S hazard. To address the safety hazards on the project, BGC developed a trigger-action-response protocol (TARP) for worker action levels related to gas concentrations and groundwater temperatures encountered during drilling.