The Edgewater Bridge carries West Mukilteo Boulevard across Edgewater Creek and straddles the boundary between the cities of Everett and Mukilteo, Wash.
The road is an important artery for the Boulevard Bluffs neighborhood and is used daily by residents, transit, ferry, school buses and emergency responders.
Built in 1946, the bridge is still safe but at the end of its useful life. Residents and transportation planners were becoming concerned as the three bridges in the area were built around the same time, and major bridge problems from a large earthquake could leave residents isolated on an island.
Granite Construction of Watsonville, Calif., won the bid-build project to replace the old five-span concrete arch bridge. The construction project cost $27 million.
Although quakes are relatively infrequent, the area did sustain a magnitude 4.6 earthquake in 2019 and a major magnitude 6.8 tremor in 2021 that rattled residents throughout Puget Sound.
Steep slopes, poor soil and frequent rains in the ravine posed another problem. The Granite construction team had to stabilize existing slopes and repair flood damage before the bridge opened for traffic. The new precast concrete girder bridge is much wider than its predecessor, as it carries two-way traffic with room for walkers and bikers.
Bradford Novy, Granite project manager, told Construction Equipment Guide that the job was a challenge for several reasons, including the unstable ground nearly 100 ft. below the bridge.
"Because the ravine was so steep below the old bridge, we had no place to put our equipment," he said. "We had to build sturdy temporary access trestles to support our equipment and work on the new bridge. Our engineers were able to come up with some outside-of-the-box access solutions that utilized the existing bridge and reduced cost to our client."
Pinned in by the geography and property lines, the project team built a temporary trestle underneath the old bridge and supported the two Link-Belt 238HSL cranes for the heavy lifting.
Workers began by removing the existing barrier on the old bridge and drilling 48 pilings from the existing bridge deck. Half of the pilings were driven through holes cut into the deck and half outside the deck. The pile pilings were 24 in. in circumference.
"Condon & Johnson Associates was our drilling partner for this project," Novy said. "They needed to fabricate custom extensions for the Kelly bar to reach the desired depth with the drill rig, as the existing grade was up to 90 feet below the bridge. Also, the slopes of the ground were unstable in some places and prone to be unstable under normal operations; this led to the use of installation by means of drilling instead of vibrating."
Another problem the drillers encountered was the remnants of an old timber-pile bridge built in 1906 that predated the current structure. The presence of these piles significantly hindered drilling production.
After the piles were installed, crews removed the old bridge piece by piece using saw cutting and wire sawing. The previously installed piles were used to reshore the existing bridge so the Link-Belt 238HSLs could operate from the existing bridge deck as pieces were removed.
Deep Shafts
After the bridge was demolished, the remainder of the trestle was built out, along with oscillator access platforms. These were used to support the construction of the large 3-meter diameter shafts to support the new bridge. Much like inserting a wood screw into a piece of wood, operators used the cranes to slowly rotate the casing into the ground.
A Liebherr 895 with a clamshell grab was used to remove the soil from the temporary shaft casing. Workers then placed rebar and poured concrete into the space created and removed the casing while concrete was being placed.
With no access roads into or out of the canyon, Granite team members lowered pieces of equipment (small excavators, manlifts, etc.) into the ravine from above with the cranes.
Beam Sled
"The center of the middle span of girders was too far from the trestle to do a single crane pick," Novy said. "Our team schemed the use of a custom-built beam sled. One crane would place the end of a girder on the sled, then the sled would be pushed to the other side on some temporary beams. Once across, the cranes could then work together to set the girders in their final position. Our engineers opted to use the original 1946 bridge columns to support this operation. It was an amazing operation to watch"
Granite said it takes safety seriously, especially with work taking place over an 80-ft. drop to the creek below.
"Our engineering team came up with many ways to minimize our workers' exposure to falls," Novy said. "Still, we made sure that our workers were educated on fall protection and what are the proper restraints to use."
The construction team used some 17,000 tons of asphalt for the bridge approaches and nearly 4,000 cu. yds. of concrete for the bridge.
Heavy rains in a community near the bridge resulted in some flooding that produced major damage on the slopes under the bridge. The Granite team fixed the problem by clearing catch basins and repairing damage. The nearby communities and Granite workers quickly resumed normal activities.
"The slopes below the bridge were quite sensitive," Novy said. "We stabilized a portion of the slope that was prone to liquefaction by removing nearly 1,500 cubic yards of poor soil and replacing it with competent material. We were able to partner with our own tunneling division to utilize a large 10-cubic-yard spoils bucket for this operation."
The new bridge opened on April 28 and restored convenience to residents. A 20-minute detour has now been reduced to a 20-second drive across the new bridge.
The community is pleased to get a new bridge, one with a sidewalk and bike lanes. Emergency vehicles can now easily pass over the bridge. And it's a bridge that is prepared for seismic activity.
"It's good to know that we have brought safety, convenience and dependability back to the area," Novy said.
