Big Sky, MT
Spanish Peaks Ski Bridge
Scope/Solutions
The Spanish Peaks, running north of Big Sky, Montana, are part of the Rocky Mountains. The developer of a mountain club was planning to construct a roadway tunnel at the base of a ski slope and over a deep-seated fault on a mountain side. Slow, ongoing ground movement occurs across the fault, and during a seismic event, the tunnel could experience up to 3 ft of lateral separation and 1 ft of downward displacement across its span. Working as part of the design-build team, SGH developed a design for the tunnel and the mechanically stabilized earth (MSE) walls at the ends that would withstand the design earthquake.
SGH designed the MSE walls and corrugated steel tunnel with a span of 36 ft, rise of 27 ft, and length of 50 ft. Highlights of our work include:
- Performing two-dimensional soil-structure interaction finite element analysis to assess the tunnel structure, including nonlinear soil and steel behavior
- Considering the moment-curvature relationship from four-point bending tests (by others) for the corrugated plate at the seam locations and away from the seams
- Using static-equivalent displacements for the seismic analysis
- Applying ductility concepts based on ASCE 41 – Seismic Evaluation and Retrofit of Existing Buildings
- Establishing an annual monitoring plan for the MSE walls and tunnel to assess the ongoing ground movement and ensure the bridge has sufficient reserve capacity to maintain life safety during a seismic event
Project Summary
2022
Key team members
