When the city of Lacey, Wash., set out to rebuild a 6,000 ft section of Carpenter Road, the main goal was to convert the two-lane arterial road to a four- to five-lane arterial.
“The challenge was that the road went through a commercial and residential area so we were really tight on right-of-way acquisition,” explained Lacey City Engineer Roger Schoessel, P.E. “We could only go so far before we were buying homes and businesses, so retaining walls and structural walls both became a huge component of the project to minimize the right-of-way requirements.”
Another challenge was that 300-400 ft of the roadway crossed a lake, which also required minimizing the road’s footprint as much as possible. To top it all off, the city had to pack multiple utilities in the same corridor.
“Through the analysis, particularly where we crossed Lake Lois, we determined that we were looking for a retaining wall system that did not require tie backs,” Schoessel said.
“From the structural wall screening criteria, we chose the Redi-Rock system because it could meet the structural requirements—it didn’t require tiebacks and it could meet the seismic code.”
The massive size of each 1-ton Redi-Rock harnesses the power of gravity, making it possible to build tall gravity walls without reinforcement. This factor allowed the city to build retaining walls in tight spaces to minimize right-of-way issues.
Aesthetics also played a role in the decision. Because the project design called for 25,000 square face feet of retaining walls, the city chose a cobblestone texture in a two-tone gray color from local manufacturer Puget Sound Precast to make sure the project had an aesthetic finish.
The project required a total of 15 separate gravity retaining walls.
Where the road crossed Lake Lois, engineers designed headwalls to flank a corrugated large-diameter pipe arch culvert to allow water to flow between the two sections of the lake. The culvert was finished using arch culvert blocks, which allowed the city to create an aesthetic look for the culvert.
Another notable section of the project included a 600-ft-long wall that consisted of two 12-ft-tall terraced walls. The top 4.5 ft of the upper wall used freestanding blocks topped off with a cap to create a railing for the sidewalk. Several other areas throughout the project used freestanding walls, columns and caps in conjunction with the retaining walls as well.
To put the scale of this project in perspective, the 25,000 square feet of walls required over 5,300 blocks—which equals roughly 8.9 million lb, equivalent to 1,379 Ford F-150 pickups.