Union County, South Dakota, has completed the first phase of replacement to two reinforced concrete slab bridges at risk of load weight restrictions and complete closure.
Structural deficiencies, including a hole in the bridge deck, led to an emergency lane closure, disrupting daily commuters and freight traffic on a key route. These bridge improvements provide much-needed relief to a community dependent on these vital connections.
Project Background
In August of 2024, Union County identified structural deficiencies in its two reinforced concrete slab bridges on 302nd Street. Recognizing the need for immediate repairs, the county bypassed the standard grant cycle, engaging Ulteig for essential engineering services.
During routine bridge inspections, Ulteig discovered increasing structural deterioration and elevated the priority of replacement on Union County’s Master Transportation Plan. Due to the proximity, separated by 1.7 miles, Union County addressed both locations simultaneously to optimize road closures during construction. However, the sites differ in design complexity; one can be replaced in-kind, and the other with a pre-cast reinforced concrete box culvert (RCBC). Ulteig was able to find immediate solutions for the most critical site while finding the best long-term solutions for the other.
Expediting Repairs
Typically, the grant application process is lengthy for projects of this scope. The timeline for the preliminary engineering and design phases can last around three years.
Knowing the time delay and urgent need for replacement, Union County decided to self-fund the preliminary engineering phase and expedite the process. Ulteig jumped into action with the client’s needs in mind to find solutions that would decrease construction and engineering efforts. Using 2D hydraulic modeling, Ulteig increased hydraulic modeling accuracy, optimized hydraulic performance, and identified a speedy and economical replacement structure – a precast reinforced concrete box culvert. The time savings to construct and design a prefabricated structure is tremendous.
This enables Union County to be on pace to replace one of the two bridges by the summer of 2025. This alleviates the highest need and will allow for the reopening of the lane closure, allowing for free-flowing traffic. The focus can then be turned to expediting the design of the other location – a continuous concrete slab bridge.
Leveraging Advanced Technology
To facilitate analysis and design, Ulteig’s team utilized 2D hydraulic modeling to accurately assess the overbank flow conditions surrounding the bridge sites. This approach is crucial for minimizing and identifying adverse impacts on nearby homeowners and their properties. Ulteig assumed that in-kind (continuous concrete slab) bridges would be necessary for replacement structures at both locations. The 2D modeling allowed for detailed bridge scour analysis, optimizing structural design and increasing resilience against significant flooding events.
To further refine their analysis, Ulteig employed multiple survey technologies, including terrestrial scanning and aerial drone surveys, which provided a precise depiction of the terrain. This invaluable data allowed for accurate modeling results and tailored design modifications to site-specific conditions. For instance, lowering the road’s elevation was a strategic move to increase roadway capacity during extreme flooding, mitigating impacts on upstream properties. In short, this comprehensive approach ensured that the engineering plans minimized environmental impact while prioritizing road safety.
Decision-Making Process
The existing structural issues heavily guided the decision-making process. A traditional bridge replacement could take a long time, so Union County wanted Ulteig to evaluate the possibility of replacing the continuous concrete slab bridges with box culverts. Due to the contributing drainage area and extent of flooding, a box culvert could only be utilized at one location.
Geometric constraints from conjoining roads further complicated the possibility of a traditional bridge design at one of the sites. Ultimately, a box culvert was not only a more efficient solution but increased construction timelines and improved roadway safety by reducing the likelihood of head-on collisions with having a long-term lane closure.
Accelerated Timeline for Safety
The project’s urgency requires a swift timeline, aiming for completion within one year of discovering the bridge deck hole, compared to a potential three-year delay. This response enhances safety and infrastructure resilience in Union County.
For the concrete slab bridge, traditional design and construction methods will ensure the lifespan of the structure is maximized. . Success hinges on finalizing designs, streamlining construction and clear communication with the community.
The second site will use a precast reinforced concrete box culvert (RCBC), allowing for quicker construction, improves hydraulic performance and increases the safety of the roadway.
Addressing both bridges simultaneously optimizes resources, reduces costs and minimizes traffic impacts. Ulteig’s collaboration will prioritize safety and best engineering practices.
As the project advances, Ulteig looks forward to its ongoing partnership with Union County to enhance infrastructure and ensure safer roadways, demonstrating that innovative solutions can lead to rapid, quality improvements.
Services Provided
