Eight of 21 large West Oahu station supports, many of them flagged by structural engineers for their growing concrete cracks, will need to be retrofitted before limited passenger service can start along Honolulu’s rail system, project officials say.

All 21 of those supports, known as hammerhead piers, will be treated with an epoxy material to help address the cracking, according to the Honolulu Authority for Rapid Transportation. It won’t be necessary to build entirely new supports at the stations as previously feared, project officials said at the agency’s board meeting Friday.

Consultants and engineers investigating the cracking have determined that the affected hammerhead piers on rail’s westside don’t pose an imminent safety concern, HART officials added.

However, it still hasn’t been made clear what’s causing those “shear” cracks, whose growth was discovered by city consultants this past summer, or how the retrofitting might affect plans to finally launch limited rail service early next year.

HART on Monday gave its initial findings to city and state transportation officials plus federal contractors overseeing the project, Lori Kahkina, the agency’s executive director, told the board. HART’s now waiting to get feedback from all of those parties, she said.

Agency officials on Friday were unable to give the board an estimate on when to expect their final report on the matter. It was originally expected in September.

That report, drawn from structural engineering consultants and the engineering firm that designed the westside hammerhead piers, is expected to give HART a consensus recommendation for fixing the problem.

“We want them all to agree on why it cracked,” HART board member Michele Chun Brunngraber said during the briefing.

Structural engineers have been running models to see where the affected structures should be reinforced to increase their lifespan, Matt Scanlon, HART’s construction director, told the board. Analysts have also focused on the measured crack widths, he added.

The problem, according to rail officials, has been isolated to the hammerhead piers that were not built with what’s called post-tensioning, a construction technique in which tightened cables help to support those concrete structures.

All of the piers built so far east of Aloha Stadium, under a separate design contract by the joint venture STG, have been post-tensioned, HART officials say.

Meanwhile, the piers’ engineer of record, HNTB, and HART’s structural engineers are still deciding the best of two retrofit methods for the affected westside piers.

That could involve what HART Project Director Nathaniel Meddings described on Friday as “post-post tensioning,” involving cables and steel plates.

The cracking has affected the pier supports at five stations, located at the University of Hawaii West Oahu, Hoopili, Waipahu, West Loch and Pearlridge, rail officials have previously said. The stations at East Kapolei and Leeward Community College don’t use the piers, Scanlon said Friday.

While the city’s consultant, Wiss Janney, initially concluded that patching and sealing would sufficiently address the issue, the hammerheads’ engineer of record, HNTB, wanted to further assess the piers’ “load-bearing capacity” and see whether additional work needed to be done.

Nonetheless, Kahikina and Meddings said Friday that the parties were not at odds with each other – at least not in terms of the piers’ basic safety.

“Both contractors confirmed and agreed that it was safe,” Meddings said.

“We want to ensure that it is better than OK, and we want to explore whether we want to take these additional retrofit steps to ensure the life of the structure,” he added, explaining HNTB’s thought process.

Kahikina said that HNTB, as the piers’ engineer of record, would get the final say on which retrofit method would be used.