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.

Key Services

  • 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

Value Added

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.