KENT — Sound Transit revealed Thursday that light-rail service to the Eastside, which was to begin by July 2023, will open a year or more later because contractors must reinforce or rebuild 4 miles of flawed concrete track supports through Mercer Island and Seattle.

Meanwhile, a landslide in Kent last month revealed that the ground was more unstable than expected, so builders must design different underground column foundations. That could delay the trains between Angle Lake and Federal Way from late 2024 until sometime in 2025.

And on the Northgate-Lynnwood extension, Deputy CEO Kimberly Farley anticipates a holdup of four to six months beyond the July 2024 target, mainly because of last winter’s four-month strike by concrete-truck drivers.

The strike is also pushing the $1.5 billion Redmond extension, to add Marymoor Village and downtown Redmond stations, toward a four- to five-month delay, after the December 2024 goal.

Farley delivered the sobering news Thursday to the transit governing board’s System Expansion Committee.

So far, the main thing lost is time, for people eager for efficient train travel and for taxpayers who’ve been paying since the 2008 and 2016 elections to fund these lines.

Farley said the problems won’t result in massive cost overruns that exceed project budgets.

No cost estimates related to these problems were released, and a report said negotiations are underway with construction companies. Events beyond Sound Transit’s control, including the concrete strike and COVID-19, would lead to longer contract deadlines, Farley said, instead of extra payments.

“We will open these transformative projects, and we will do so as rapidly as possible, with our chief priority being our passengers’ needs for safety, quality and long-term durability,” interim CEO Brooke Belman said.

Sound Transit previously acknowledged its $3.7 billion, 14-mile line from International District/Chinatown Station to the Overlake area would miss its July 2023 grand opening date because of flaws in concrete track supports, where rails are being laid over the former Interstate 90 express lanes.

But the project team discovered worse conditions as recently as June.

Contractor Kiewit-Hoffman is expected to partially replace the top 6 to 18 inches of these concrete blocks, known as plinths, or to surround them with reinforcing materials, said Jon Lebo, Sound Transit’s executive project director for East Link. Contractors and advising engineers will conduct tests of different methods, he said.

Problems were first discovered in 2019, and Sound Transit approved the use of mortar to adjust the plinths, which failed. Workers have been lifting rails this year, to grind and resurface plinths that were built incorrectly to the wrong dimensions or contained weak concrete.

“We thought we had a solution to the problem that we were confident would work … Unfortunately, the solutions we put into place failed, and every time we went to implement a new solution, we found more issues,” Farley said. Digging deeper, officials discovered too much or too little rebar near surfaces.

The troubled areas total 4 miles and 5,455 plinths, Lebo said.

Another kind of track support, on the I-90 floating bridge deck, was structurally sound, but about 1% of the customized nylon inserts became stripped after metal rail fasteners were bolted in. All 19,400 bolt inserts are being replaced and strengthened by epoxy.

Farley said that, fortunately, “our relationship with the contractor is quite good. We’re in solution mode, to find out how to resolve these issues rather than point fingers at each other.”

The most recent Agency Progress Report, as of June 30, mentioned errors and delays blamed on other contractors across multiple segments of the Eastside line. Those challenges range from inadequate bearing pads under elevated track bed girders to a lack of train clearance at a curve inside Bellevue Downtown Station to a partial rebuild of the Redmond Technology Station parking garage, where some concrete beams weren’t strong enough.

Repairs are either completed or likely to be done before the I-90 problem is solved.

A small shelf of crumbling dirt in Kent, about 200 feet long and 9 feet high, caused a three-day closure of a southbound Interstate 5 lane in mid-July, to stabilize the area near South 259th Place, where Sound Transit will build aerial guideways.

That was the tip of the iceberg.

Sound Transit says contractor Kiewit-Hoffman now needs to engineer special foundations, so that trackway columns will support girders and trains despite the liquefiable soil.

Columns are generally 50 feet deep, while the unstable soil is 0 to 40 feet deep, spokesperson David Jackson said. So the modified columns mainly need to resist lateral force in the event of an earthquake.

The site was quiet Thursday morning, with no crews in the troubled area marked by plastic sheets and a partial retaining wall, as construction continued farther south.

Farley said some other challenges await for the $2.5 billion project, such as how to construct and control traffic access roads, mainly at Federal Way Downtown Station.

Contractors poured the wrong kind of small rock to ballast the rails in North Seattle, between Northgate Station and the approach to future Northeast 130th Station. But they rapidly substituted better-grade material this summer, to avoid triggering delays, spokesperson John Gallagher said.

A greater problem was the four-month concrete-drivers strike that interrupted some crucial pours and caused layoffs in the 8.5-mile, $2.7 billion project from Northgate to Lynnwood, officials said.

The 1,670-space parking garage at Lynnwood City Center Station was affected by the strike. Farley said train service can begin before garages are completed, if need be.

Project reports point to broader problems, throughout the industry, of too few skilled trades workers, megaproject engineers and supervisors. That’s a potential obstacle to some quality-control steps Farley described, such as more inspections.

In a staff memo, Sound Transit accepted some blame for failing to audit contractors’ quality assurance and quality control rigorously enough, to find problems earlier.

A June progress report also mentions the risk that there won’t be enough operations experts who can conduct months of train tests when the tracks are finished, which could happen simultaneously on two or more lines, and “blind spots” where glitches don’t get discovered because technical staff familiar with the project move to other jobs, reports say.

Delays on the Eastside might result in Bellevue and Redmond tracks opening at or near the same time, but Farley said it’s too soon to know.

And if the Bellevue line — which includes a new train maintenance base — takes longer to finish than the Lynnwood or Federal Way segments, that would foul up the overall railcar supply, and possibly the frequency or train length across the metro area. Farley said staff are already thinking about strategies, and will know more late this year, when they publish new goals for grand opening dates.

Committee Chair Claudia Balducci of Bellevue, who has worked for 15 years toward delivering Eastside rail, suggested that if I-90 isn’t usable on time, Sound Transit should either beef up its Route 550 express bus across Lake Washington to rail-like quality, or even operate a light-rail segment reaching Eastside stations only. (Former Redmond Mayor John Marchione mentioned that notion years ago, in the event the unprecedented floating bridge route is unbuildable.)

Belman emphasized that East Link is the region’s most complex transit project to date.

“This is truly historic. No other region of our country has so much transit infrastructure concurrently under construction and preparing to enter service in such a compact timeline,” her memo says.

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