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SR 92/Little Pilchuck Creek

Lake Stevens, Washington

Government

Contractor:

Graham Construction and Castle Walls, LLC

Keystone Producer:
Mutual Materials

Installation:

2018

Technical Description:

• 66' span x 24' rise x 72' long BEBO® Bridge Concrete Arch System
• 4,800 SF of Keystone Compac® II Retaining Wall System

This Washington State Department of Transportation (WSDOT) culvert replacement project was part of a long-range, federally mandated, "fish passage" program to restore impeded fish migration that has been an unintended consequence of outmoded state roadway culvert design. Before the culvert renovation, migrating fish traversed a very constricted and fast-flowing stretch of creek through a 12' wide x 6' high box culvert under State Route 92 in Lake Stevens. After the culvert was replaced with a 66' wide arch bridge, the creek was widened back to its natural state, restoring the water speeds to what nature intended. Once installed, the new bridge was backfilled so that SR 92 could be reconstructed over it.

Out of the three precast structure options shown on the bid drawings, the winning bid submitted by Graham Construction used a 66' span x 24' rise BEBO® Bridge Concrete Arch System, 72' in length, along with 4,800 sf of the Keystone Compac® II Retaining Wall System for the headwalls and wingwalls. This package met WSDOT criteria and was selected as the best culvert replacement option for its ability to provide a quality product, cost savings, minimal long-term maintenance and, most importantly, an accelerated design and installation schedule. Additionally, the new, wider passage allows the creek to flow more naturally under the highway, which in turn, improved fish passage over 30 miles of water habitat. The BEBO structure was installed via two cranes in just 24 hours, and the road itself was closed for only 13 days.    

The arch headwalls and wingwalls were constructed with the Keystone structural wall system, which has been approved by WSDOT for use on state and federal highways. The total area for the two walls was 4,800 sf with the size of each wall 160' long and a maximum height of 29.7'. Design considerations included the tall wall height, 2H:1V backslope, and high seismic acceleration requirements. Due to its inherent flexibility, the Keystone retaining wall system has shown considerable resistance to seismic forces, permitting minor yielding during a major seismic event, particularly when compared to other more rigid wall systems.

With a one square foot face area, the easy-to-handle one-foot-deep Compac unit furnishes exceptional structural performance. The unit is made of high-strength, low absorption concrete and for interconnection and alignment, uses fiberglass pins that achieve strong shear connection and provide a secure connection with soil reinforcement materials. Face textures include tri-plane or straight split options that have a weathered symmetry, coloring and appeal. Compac Hewnstone’s face has the look and feel of naturally chiseled stone.

The Keystone product was produced by Mutual Materials of Kent, Washington, and the wall designed and engineered by Keystone. Installation was performed by Castle Walls, LLC, Issaquah, Washington. Compac units are designed to the highest standards and unique requirements of the transportation sector and have been approved by 27 state highway departments.

In this case and for similar projects, an undersized culvert was upgraded with a larger, fish-friendly structure. Miles of rearing and spawning habitat, which had become inaccessible when roadways in the state were constructed over these environmentally sensitive waterways, have been restored to protect fish populations.

Technical Description:

• 66' span x 24' rise x 72' long BEBO® Bridge Concrete Arch System
• 4,800 SF of Keystone Compac® II Retaining Wall System

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