By: Dan Wasniak, PE
To improve safety for drivers along Highway 24, the Colorado Department of Transportation developed a plan to make several changes along a 5–mile route in Lake County. Because of the area’s harsh winter weather, the road was in poor condition and needed resurfacing and regrading. Additionally, the highway’s narrow width and blind spots were causing frequent accidents.
The plan included reconstruction of two 12–ft lanes and 6–ft shoulders, new guardrails and flattening of the slopes. CDOT also needed to remove a deficiently sized structural plate pipe and replace it with a bridge that would span the Arkansas River.
Twin 12– x 10–ft cast-in-place concrete box culverts were originally proposed for the bridge project. CDOT had plans to open cut the road and construct the bridge in two halves, with total expected completion time estimated at three to six weeks. However, goals aimed at keeping road closure time to a minimum, and concerns over environmental impact led CDOT to consider other options.
Tezak Heavy Equipment approached CDOT to propose CON/SPAN as an alternative solution. The system, with precast modular components, was cost-efficient and fast to install. The 24–ft span, precast arch structure was installed over the existing pipe, allowing the river to flow freely through the pipe until the arch units could be installed and backfilled.
Using a conventional cut-and-cover method, Tezak was able to install the bridge easily and remove the pipe. Once the footings were cast, installation of the new bridge and removal of the existing pipe was completed in just three days.
“One of the main reasons we did this bridge option was to speed up the construction, since this is a major route for Leadville,” said Clinton Moyer, P.E., project engineer for CDOT. “Also, aesthetically, it is a knockout compared to a twin box.”
The clear span structure also minimized environmental impact to the river, which is home to native-born brown trout. With the bottomless system, the streambed could easily be returned to its natural state, and the precast components allowed construction crews to complete installation without diverting this part of the river.
