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Slim cracks are growing in the concrete columns that support most of the elevated stations along the western half of Oahu’s future rail line, posing a new and “potentially significant” problem that could delay the system’s interim opening even further, according to project leaders.

Contractors hired by the city’s Transportation Services Department discovered in recent weeks that those cracks have grown, leaders told the agency’s board Thursday.

They’ve advised that passengers not be allowed into the seven affected stations until further inspections are done, HART Executive Director Lori Kahikina said.

“I don’t have all of the answers at this time,” Kahikina told the board during its latest general meeting. “The root cause, I don’t know. More research and analysis needs to be done.”

The cracking problem, Kahikina and her deputies say, appears limited to the special hammerhead-design piers that hold up the western stations along rail’s elevated guideway. Those concrete-and-steel piers were built in 2014 by former rail contractors and .

The problem appears limited to piers that aren’t reinforced with what’s called a construction technique in which tightened cables help to support those concrete structures’ piers, HART Project Director Nathaniel Meddings said.

It wasn’t clear Thursday why not all of the hammerhead piers were reinforced with that post-tensioning. Kiewit and HNTB completed their work through a “design-build” contract, in which the construction contractor handles the design work as well as the building.

The cracks causing the problem are known as shear cracks, which typically form in a diagonal slant across the surface, Kahikina said.

In years past, some West Oahu residents as well as critics of the transit project have flagged visible cracks in the rail columns as a potential problem, although HART has said there was no reason for concern. Some cracking in concrete construction occurs normally and isn’t a problem, rail board member said Thursday.

However, when the cracks start to form at a 45-degree angle it’s a concern, Meddings said later, and “that’s what we’re seeing out there.”

From the discussion Thursday, it wasn’t clear exactly when the cracks formed, but HART officials said that crews have been aware of them on those piers for years and that they check them for potential problems every two years.

The DTS contractors discovered the cracks’ growth as that city agency prepares to take over the rail line’s first 10 miles for passenger service. The widest cracks found are about a tenth of an inch wide, according to Kahikina.

Roger Morton, who sits on the HART board as DTS director, said he was disappointed by the discovery but “safety has to be the overriding concern for this.”

The former contractors who built the piers have already flown out their own teams to inspect the structures, according to Kahikina and Meddings. HART, DTS, their consultants on the matter and the engineers who were responsible for those piers will spend at least the next two weeks assessing the situation and deciding what needs to be done, Kahikina said.

“We’re not rushing through this,” she said.

Earlier this summer, the HART director said at a press conference that her agency was aiming to start the rail system’s required 90-day trial running sometime this month. That needs to happen successfully before passenger service can start. The trial running was later to pushed to Aug. 1, said Jade Butay, who sits on the HART board as the state transportation director.

Now, that August start date looks “way too aggressive,” Butay said Thursday.

The cracking issues affecting rail’s western half are not likely to impact the 5 miles under construction around the airport because all of those hammerhead piers are reinforced with post-tensioning, Meddings said.

‘We Hope This Is The Last Issue’

This isn’t the first time that the rail agency has had to address premature cracks forming along the rail line. Contractors previously had to replace cracking plastic pads along the track, and steel canopy arms that had cracked due to faulty manufacturing.

More recently, the agency has been besieged by multiple problems affecting the track layout, wheel dimensions, and the precise points where the tracks intersect along the crossings, called frogs. HART has said that it’s effectively addressed those problems.

However, documents show that the agency was aware of the design flaws years earlier than it previously disclosed, and a former project consultant and whistleblower has said those flaws will still cause major maintenance headaches and potentially safety issues in the long run.

HART declined to clarify after the meeting which stations are affected by the shear cracks in the piers and when those cracks were initially discovered.

“We hope this is the last issue,” Meddings told board members earlier in the day, referring to the pier cracking.

Meddings added, however, that he couldn’t say it would be the last problem from HART’s past “that’s going to jump up and bite us.”