Crumbling Steel Culvert Gets Precast Concrete Upgrade

Lewis County, Washington

Crumb Road was already crumbling when winter storms scoured a section over Highland Creek and rendered it temporarily impassable. Major flood events rained down on Lewis County, Washington in early 2020, and the old corrugated metal arch pipe culvert under Crumb Road was damaged beyond repair.

“We needed an economical solution to restore unrestricted traffic on Crumb Road,” says Rodney Lakey, PE, project manager for Lewis County Public Works.

While the extent of the overall damage qualified Lewis County for Federal Emergency Management Agency funding, the replacement structure for Crumb Road would need to follow FEMA’s minimum specifications to restore traffic to preflood conditions, all the while staying within budget. Moreover, because Highland Creek is a fish-bearing stream used by migrating salmon and steelhead trout, the replacement also needed to meet Washington Department of Fish and Wildlife guidelines.

Lewis County considered installing a bridge at the damaged site.

“On this particular site, we had very poor soils underneath,” Lakey says. “It was not a typical installation. To put in a bridge would have essentially meant drilled shafts socketed into bedrock that was down anywhere from 45 to 65 feet. The bridge option was quite a bit more expensive because of the drilled shafts into the rock layer below.”

Ultimately the county decided on precast concrete culvert that met both the federal and state requirements while saving a lot of time and money. Plus it will last longer than steel in virtually any weather event.

Meet Every Requirement

The Highland Creek streambed under Crumb Road was so unstable the county opted to construct a wood pile supported load transfer platform under the precast concrete culvert to provide a secure bed. The support system includes timber piles at 5’ on center below alternating layers of biaxial geogrid to provide a stable culvert base.

Precast placement started once the streambed preparations were complete. Because of in-water work restrictions, Lewis County needed to purchase culvert materials by a certain date, so the county obtained the 20 precast sections directly from Jensen Precast while site preparations were ongoing. Contractor Quigg Bros. Inc. managed the timing of delivery.

Jensen Precast in Puyallup, Washington, worked with the engineering firm Pretek Group to design a culvert replacement that would meet every requirement. Each section consists of two three-sided culverts that form a box. Each U-shaped piece is 30’-8” wide by 6’ in length. Ten box sections create a 60’ overall culvert length to support Crumb Road above, and a 29’ wide structure to enable fish passage in Highland Creek below.

“Each culvert section is about a 30’ span and weighs more than 40,000 pounds,” says Tim Nyhus, Jensen Precast Puyallup Plant Manager. “These are massive pieces of precast concrete. It was the largest span culvert that we’ve done at our location.

“This culvert is on the larger end of a three-sided culvert. In Washington, they will allow a three-sided culvert to reach a certain span with mild reinforcing. Then, once it reaches a certain span, alternative measures must be used, like short-span girders.”

Restored Road and Streambed

With fish passage culvert replacements, a prescribed fill of natural rock and soil is added to the streambed after the precast bases are installed to return the stream to its natural state.

“The two U-shaped pieces make it easier to install the streambed material,” Nyhus says. “Depending on how the structure is configured, once the bases go in, the contractor comes back and adds the fill to a prescribed height. Once the fill is in, they install the tops.”

Replacing an undersized corrugated steel pipe with a 30’ wide precast concrete box culvert structure provides long-term support for the vehicles using the Crumb Road above and creates a natural streambed environment for the migrating fish below. For Lewis County, the precast solution proved to be a win-win.

Jensen Precast specializes in manufacturing precast concrete monolithic and segmental box culvert. Get a quote for your project now.

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