The 2024 ACEC/Iowa Engineering Excellence Awards winning projects in the Special Projects Category:
Special Projects Grand Place Award (1st Place in Category)
Firm: Strand Associates, Inc. Client/Owner: City of Dubuque Project: Bee Branch Creek Railroad Culvert and Pedestrian Tunnel Project
Project Description Historic Flooding Issues Combined with Stringent Railway Requirements Make for Complex Railyard Crossing Project The City of Dubuque has a history of localized storms that sends stormwater rushing quickly off steep bluffs to the flatter areas where it then slows and ponds eventually making its way to the Mississippi River. Construction of a levee system in the early 1970s provided protection from the Mississippi River flooding but complicated the localized City drainage system. Over a 12-year period starting in 1999, the City suffered through six, localized flash flooding events that resulted in Presidential disaster declarations.
With tens of millions of dollars in both public and private property damage in 2011 the City began implementing the multi-phase Bee Branch Watershed Flood Mitigation Project. The third phase, completed in 2022, involved improvements to pass stormwater and connect pedestrians from the Upper Bee Branch through an active Canadian Pacific and Kansas Southern railroad (CPKC) rail yard to the Lower Bee Branch.
The proposed construction corridor through the CPKC yard was bounded by a railyard maintenance building, a furniture store, industrial storage buildings, and the Lower Bee Branch Creek. Additionally, the active railyard would remain fully operational during project construction, so little track settlement would be permitted. This made geometric layout and construction staging challenging. In addition, the hydraulic demands of the proposed gravity culvert system and pipe cover requirements of CPKC limited options for the installation of a conveyance system and pedestrian pathway.
Creative Engineering Meets All CPKC Requirements While Exceeding City’s Expectations for Attractive, Sustainable Infrastructure The project team coordinated closely with CPKC and conducted extensive geotechnical investigations, structural evaluations, and hydraulic analysis before employing micro tunneling as the proposed construction solution. The team designed six, 101-inch-diameter steel stormwater culverts to convey up to a 500-year storm event safely beneath the CPKC railyard. The team also designed the conversion of the existing twin, 11- by 10-foot concrete box culverts to a pedestrian tunnel, providing a grade-separated rail crossing and connecting the 30-mile Heritage Trial system to the Mississippi River Trail. Continuous monitoring was required to ensure minimal settlement of the railroad tracks above the tunnels. Ground penetrating radar and 3D laser scanning were also used to assess and design repairs to the twin box culverts. The use of interlocking mechanical joints to connect individual sections of pipe for trenchless construction of each of the six steel pipe culverts that varied in length from 190 to 200 lineal feet aided in reducing overall tunnel construction time to just 4 months. This project successfully improved stormwater conveyance and accessibility of a pedestrian multi-use path by using creative engineering tactics to exceed stakeholder needs for the Bee Branch Creek Railroad Culvert and Pedestrian Tunnel Project.
