Bozeman Bridges

This project consisted of the design and construction of three bridge replacements and four seismic retrofits for seven separate structures along Interstate 90 in north Bozeman, Montana.

Bridge Replacement

• North 7th Avenue Interchange
• Eastbound and Westbound P-86/Montana Rail Link Structure
• Eastbound and Westbound Montana Rail Link Spur Line Structure

Seismic Retrofits

• Eastbound and Westbound Valley Center Road Separation Structures
• Eastbound and Westbound L Street Separation Structures
• Eastbound and Westbound Fort Ellis Road Separation Structures
• Bear Canyon Interchange Structures

The bridge replacements will consist of demolition and replacement of the existing structures in a staged construction. The new bridges will be supported on a combination of driven pile and spread footing foundations. The seismic retrofits will generally consist of upgrading the existing bridge foundations, superstructure and bridge decks to meet current seismic design standards. Our scope of services for the projects included the following:

• Performing review of available geologic and design information, and performing a geotechnical reconnaissance to identify potential geotechnical issues and establish boring locations for the replacement structures.
• Evaluating allowable bearing pressures, seismic-induced settlement and liquefaction potential for the existing and proposed spread footing and driven pile foundations.
• Developing appropriate seismic parameters for the spread footing and pile foundations.
• Performing a total of 18 soil borings with an AP1000 percussion drill rig to extend the borings through very dense gravels, cobbles and boulders to evaluate soil and bedrock conditions for the replacement bridge structures.
• Conducting laboratory tests, including sieve analysis, Atterberg limits, specific gravity, moisture content, and corrosion on geotechnical samples.

Upon completion of the fieldwork, reports were prepared for both the seismic retrofits and bridge replacement projects. The seismic retrofit reports provided analysis and recommendations regarding seismic-induced settlement, liquefaction potential, allowable bearing pressures for existing spread footing foundations, allowable axial and lateral pile capacities for existing timber pile foundations and appropriate seismic soil parameters for design of the seismic retrofit. For the bridge replacement projects, analysis and recommendations were provided for driven pile and spread footing foundations. Recommendations consisted of allowable axial and lateral pile capacities for steel pipe pile. Estimated settlement and allowable bearing pressures for spread footing foundations and lateral earth pressures for abutment wall design. Estimates of seismic-induced settlement and liquefaction potential were also evaluated.