Updated Oct. 21, 2026

This page provides in-depth information about some of the larger construction efforts related to the SR 520 Portage Bay Bridge and Roanoke Lid Project. It will be updated when significant construction elements call for additional information.

Piledriving and drilled shaft work continues this fall and winter

Learn where crews will be working and what neighbors can expect

Photo (looking west) of piledriving activities near the eastbound SR 520 off-ramp to Montlake Boulevard (October 2026)

Where we’re working

Neighbors and travelers should expect to see or hear a consistent level of construction from these areas on each end of the existing Portage Bay Bridge through at least the end of Season 3 (April 30, 2027). The table below lists the piledriving and drilled shaft installation locations.

Piledriving locations	Drilled shaft installation locations
West end of Portage Bay Northwest trestle crane platform (near Boyer Avenue East) East end of Portage Bay Temporary Bridge 2 (near the Montlake lid) Northeast trestle area (“fingers”; near NOAA)	Bridge Piers 1 and 2 (Boyer Hillside, north of SR 520) Lid Pier 1 (south of SR 520) Lid Pier 4 (north of SR 520) Pier 5 (I-5 Trail Crossing Bridge)

Piledriving methods and schedule

Impact vs. vibratory piledriving

Crews use two types of hammers to drive piles: vibratory hammers and impact hammers.

• Vibratory hammers use rapid vibrations to “shake” piles into the ground. This works well in Portage Bay’s softer clay and sediment layers, where the vibrations help each pile break through the soil. This method creates a steady, continuous sound and vibration. We use vibratory hammers whenever possible.
• Impact hammers repeatedly drop a heavy weight onto the top of the pile to drive it through harder soil. This method creates a sharp, repeated banging sound. We use impact hammers when piles reach dense clay layers that won’t give way to vibration alone.

Reminder: Typical impact piledriving hours are 8 a.m. to 5 p.m. on weekdays and 9 a.m. to 5 p.m. on weekends, though we may work later into the evening if needed.

Impact and vibratory piledriving in and around Portage Bay

The project includes six seasons of in-water impact piledriving. We are currently in Season 3, which began Sept. 1, 2026, and continues through April 30, 2027. Neighbors can expect intermittent piledriving throughout the project area during this time. Crews will use both vibratory and impact hammers.

Piledriving locations: West end of Portage Bay

Northwest trestle “island” near Boyer Avenue East

Starting in November, crews will begin installing 36 piles near Boyer Avenue East on the north side of SR 520. We will use these piles to create a temporary work platform to construct bridge pier 3 on the land west of Boyer Avenue East. We expect this work to take approximately two months to complete both installing the piles and building the platform.

Piledriving locations: East end of Portage Bay

Northeast work trestle ‘fingers’

Crews will also be piledriving on the north side of SR 520 near NOAA. Crews will use these piles to l build new “fingers,” which are extensions of the work trestle. The fingers provide the space needed to install additional drilled shaft casings in the future. Crews will also install piles to create temporary support structures, called “falsework,” that will be used to support future bridge construction.

We anticipate this work to begin in late October before taking a brief pause to facilitate a needed traffic switch in early 2027. Neighbors can expect piledriving in this area to resume after that switch and continue for at least the remainder of Season 3.

Temporary Bridge 2 (SR 520 mainline shift) near the Montlake lid

Beginning in late September and continuing through the fall and into winter, crews will install piles between SR 520 and the eastbound SR 520 off-ramp to Montlake Boulevard. Crews have already installed half of the required piles in this area. These piles will be used to create a retaining wall to support a new temporary roadway called “Temporary Bridge 2.”

The new temporary roadway will be built later this year. In early 2027, both eastbound and westbound traffic will shift onto the temporary bridge so crews have room to build the remaining piers for the new westbound bridge.

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Drilled shaft installation methods and schedule

Crews will install drilled shafts to form the permanent foundations for the new bridge and lid. This work involves installing steel casings, removing soil from inside them, placing rebar cages and pouring concrete.

Drilled shaft installation locations

Lid Pier 4 (south of SR 520 / near East Roanoke Street and Delmar Drive East)

In late August, crews began removing old underground H-piles (piles that look like the letter “H”) and steel sheeting in the area south of SR 520 between 10th Avenue East and Delmar Drive East. Crews completed H-pile and sheeting removal in early September. Crews are now installing drilled shaft casings using oscillators. Oscillators rotate the casings back and forth into the ground. We expect these oscillators to produce less noise and vibration than impact or vibratory hammers.

After each casing is installed, crews remove soil from inside the casing, place a rebar cage and pour concrete to form the permanent foundation. This work will continue through the fall and into winter.

Bridge Pier 1 & 2 (Boyer Hillside, north of SR 520)

Crews completed the initial phase of regrading the hillside between Boyer Avenue East and East Roanoke Street in September. Crews have begun moving equipment and materials needed for the next phase of bridge construction: building on-land bridge piers 1 and 2.Starting this fall, crews will begin installing drilled shafts that will form the permanent foundation for the new westbound bridge. Like the lid pier 1 work south of SR 520 , crews will install casings, excavate inside the shafts, place rebar cages and pour concrete. This work is expected to continue through winter.

Looking ahead

As a reminder, we are in our third of six in-water impact piledriving seasons, which continues through April 30, 2027. During the remaining seasons, crews will conduct intermittent in-water piledriving to expand the temporary work trestle, build temporary supports called “falsework” and construct other project elements.