The replacement bridges are four-span, approximately 850 feet long with spliced concrete beams and concrete bridge decks. The bridge elevation decreases by approximately 40 feet from the south to the north. The bridge is 100 to 150 feet high above the Williams River and GMR track. The replacement bridges and approaches are wider than the previous roadway, requiring widening of the bridge approaches. The north abutments were constructed on existing fill embankments over 100 feet in height and of variable density, over natural alluvial and glacial till deposits.
The Solutions Unearthed
- After driving piles through dense embankments for the northbound abutments, the team redesigned the southbound pile foundations, taking advantage of Pile Driving Analyzer (PDA) pile testing data.
- Using the PDA data, the team was able to utilize a larger number of lower capacity piles to significantly reduce overall driving lengths, driving difficulty and number of splices.
- We used geophysical seismic refraction and GPR measurements to obtain geological data on the river channel for scour analysis. The geophysical work saved time and money compared to conventional soil borings from a river barge or from the bridge deck above.
- We performed a site-specific geotechnical seismic hazard evaluation including a ground motion study to develop a design response spectrum and liquefaction evaluation based on an earthquake with a 2,500-year return period due to the “critical bridge” designation.
- We determined adequate global stability safety factors for the existing and widened embankments without the need for additional mitigation measures initially considered during preliminary evaluations.
- Our ability and commitment to providing timely and practical design and construction recommendations have been crucial for a fast-paced design-build project such as this.
Client: HDR, Inc.