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News / Northwest

Bad light-rail ties on I-90 bridge can’t be fixed, must be rebuilt

By Mike Lindblom, The Seattle Times
Published: April 14, 2023, 7:47am

SEATTLE — After some futile attempts at repairs, Sound Transit contractors have scraped thousands of flawed concrete track ties from the decks of Interstate 90 so new ties can be built from scratch.

This second effort by the Kiewit-Hoffman partnership delays the Lake Washington train crossing beyond the mid-2024 target announced last summer, when the agency revealed that 5,455 concrete supports, known as plinths, were deficient from Seattle to Mercer Island.

Workers previously tried mortar patches, or jackhammered away the tops of plinths, to recover and fortify flawed areas — similar to a dental filling.

That strategy has been abandoned.

Kiewit-Hoffman decided in late September, after mortar failures and a forensic investigation, that the best plan is to start over, according to Sound Transit. More than half the plinths were demolished and some rebuilds begun last fall, Deputy CEO Kimberly Farley notified board members in November.

Sound Transit’s latest timetable is to carry light-rail passengers across the lake by spring 2025. Demolition of the original plinths is nearly complete, and the track rebuilds will expand to six work zones this month, staff reported Thursday in an update to the board.

Long stretches of the former I-90 express lanes are bare, while rows of tents shield new work zones.

Contractors added staff in April, and the agency’s managers have kept in daily contact, reported Ron Lewis, Sound Transit’s executive director for design, engineering and construction management.

“They made a concrete pour on Tuesday this week, and more are scheduled in the coming days,” he said.

However, he also said track rebuilding has gone slower than planned, and unless the pace quickens immediately, Sound Transit will miss the spring 2025 grand opening goal.

Project managers say they first became aware of plinth problems in 2019, such as too much or too little steel rebar near the concrete surfaces, some voids, or plinths not tall enough. They didn’t reveal a schedule crisis until April 2022, after trying adjustments such as mortar patches and surface grinding.

These 5,455 plinths sit upon 4 miles of fixed, mainly overland deck spans of I-90 in Seattle and Mercer Island. A second, less-vexing problem involves precast concrete blocks on the floating bridge that are structurally sound but need new, stronger nylon bolt inserts where the rails are fastened. A third type of track ties, where concrete blocks are nestled within gravel ballast, are doing fine.

Transit executives have been chastised by outside experts for not airing bad news quicker. But on Thursday, board member Kent Keel of University Place praised the staff and new CEO Julie Timm for increased transparency in recent months.

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Kiewit’s headquarters in Omaha, Neb., did not reply to a request for comment Thursday.

“Our construction contractor has been working with us to resolve these issues,” Sound Transit Chief of Staff Brooke Belman said last summer.

It’s not clear yet how much extra pay Kiewit might claim, but the board last month did approve a potential $14 million contract increase to compensate for the nylon-fastener issue. The causes for this flaw are still being investigated. That boosts the I-90 segment construction contract to $736 million from Seattle to South Bellevue.

Once a workable trackway is complete, additional weeks are necessary to test the train fit, power and signals, followed by at least 60 days of full-speed practice trips. During this break-in period, engineers must also confirm that their exotic transition joints keep the rails parallel and flex precisely as designed, before trainloads of people travel 50 mph between fixed roadway decks and moveable bridge pontoons. This is the world’s first rail transit on a floating span.

Ironically, the plinth mess might increase the odds that Bellevue and Redmond travelers get to use a local Eastside line first in spring 2024 — between South Bellevue and Redmond Technology stations — before Lynnwood train service begins.

Before they can fully serve Lynnwood, transit operators need a finished I-90 crossing, where trains can move from a new Bellevue maintenance base to the University of Washington, Northgate and Lynnwood. Until then, Lynnwood can’t receive the promised capacity of one train every four minutes, transit officials say. The fear of a crowded Lynnwood line creates political momentum to open the so-called Eastside Starter Line first.

The whole $3.7 billion, 14-mile East Link route, from International District/Chinatown Station to Redmond Technology Station, was approved by voters in a 2008 sales-tax measure. The public was promised a 2020 grand opening, which lost three years amid route-alignment disputes between Sound Transit and Bellevue.

Lewis and Belman also reported Thursday that construction for both the Lynnwood and downtown Redmond extensions is showing “positive float,” meaning the crews are on track to finish days ahead of schedule.

That progress raises a question for later, Lewis said. If the downtown Redmond job keeps humming along, and the I-90 rework is slow, it might make sense to combine two more train stops at downtown Redmond and Marymoor Park with the rest of the eight-station Eastside starter line.