Under their IDIQ contract with the Confederated Salish Kootenai Tribes, DJ&A was tasked with providing survey and design for the replacement of ten bridges across Lake County in Montana. The largest structure, the 158-foot span South Valley Bridge, demonstrates DJ&A’s technical competence in the design of longer-span vehicular bridges.
The existing single-lane bridge on South Valley Creek Road was replaced with a double-lane steel plate girder bridge with composite cast-in-place concrete deck support by abutments on steel H-piling. DJ&A analyzed and reviewed bridge and roadway alternatives, provided a hydraulic analysis, designed the re-alignment of the roadway approaches, and performed final structural design calculations.
Key elements of the design included increasing the bridge span to provide for adequate freeboard over the 100-year flood elevation and reestablish floodplain areas under the bridge. The horizontal and vertical alignments of South Valley Creek Rd. were designed to improve sight distance and meet AASHTO standards.
- Performed site survey, topographic mapping, hydraulic analysis and structural design
- Prepared road and bridge construction plans, specifications and cost estimates
- Prepared right-of-way documents
- Facilitated pre-construction meetings
- Assembled as-built drawings
DJ&A provided an early and accurate cost estimate that allowed the Tribe to accurately program the cost of the project. DJ&A delivered this large project on time, under budget, and without any design change orders.