Damaged “hammerhead” rail station supports that have come under scrutiny are structurally sound; however, plans are pending to repair hairline cracks in 21 of them to ensure their life spans, the head of the Honolulu Authority for Rapid Transportation said.

None of the cracks is wider than eight-thousandths of an inch, Lori Kahikina, HART CEO and executive director, told the Honolulu Star-Advertiser on Thursday. Thirteen of the smallest cracks can be repaired by filling in with epoxy to keep out moisture and reduce the possibility of further cracking, she said.

For the other eight hammerheads, discussions are turning to the possibility of a combination of adding rebar, steel plates and tension cables that also “will add strength to the overall structure,” according to Rick Keene, HART deputy executive director.

The plan is to retrofit the eight hammerheads so “that they will have a longer life and will also add additional strength,” Keene said.

One early idea was to encase the most seriously damaged hammerheads in “carbon fiber wrap,” similar to repairing cracks in bridge columns. But the design of the rail columns involves a more complicated process of installing separately constructed T-shaped hammerheads atop the rail columns to support the rail stations.

So the carbon fiber wrap idea has been abandoned.

“We don’t think that will provide enough structural strength,” Keene said.

The columns support the rail tracks and trains. The hammerheads support rail stations and do not affect ongoing testing of the system to work out any problems before turning it over to the city Department of Transportation Services for paid ridership sometime in 2023, Kahikina said.

Testing of the rail system currently underway involving 144 scenarios is two-thirds complete, Kahikina said. For example, one current focus of testing is on a software glitch that allows communication to one train and one station but not to multiple trains and multiple stations simultaneously.

The remaining scenarios are expected to be even more complicated, Kahikina said.

She and Keene emphasized that the purpose of the “trial running” phase is to identify and fix problems before regular ridership begins. “That’s the whole point of trial running,” Keene said.

Ideally, the rail officials said, the hammerhead repairs will be complete around the same time HART completes its trial-running phase.

In the short term, engineers from the Federal Transit Administration, state Department of Transportation, city Department of Transportation Services and HART all will have to agree on how to fix the hammerhead cracks once engineering firm HNTB — the rail project’s engineer of record — issues its final report, expected the first week of December.

The cracks were discovered in 2018 and were assumed to have been caused by concrete shrinkage, similar to what occurs in a new concrete driveway, Kahikina told the City Council Committee on Transportation, Sustainability and Health on Tuesday.

But no one took precise measurements until June, which showed the widened cracks were “more than what is typical of shrinkage,” Kahikina told the committee.

The $9.8 billion project, as currently approved by the FTA, calls for a truncated route of 19 stations along 18.75 miles of track from East Kapolei to the planned Civic Center station in Kakaako.

Kahikina on Tuesday called the Civic Center station the “temporary” end of the line, and she described the elimination of the Pearl Highlands parking structure a “temporary deferral.”

Discussions are underway to find new sources of funding to push the rail system to the previously planned Ala Moana Center station “and beyond,” including ways to provide service to North Shore and Central Oahu passengers, Kahikina said.