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Workers from TPA Construction work atop a lift in the Dornan Drive Tunnel in Richmond, Calif. on Monday, Feb. 11, 2013. Crews recently discovered significant concrete failure in the tunnel wall, prompting a complete closure of the tunnel. (Kristopher Skinner/Staff)

RICHMOND -- Workers discovered concrete failure inside the nearly century-old Dornan Drive Tunnel on Friday, forcing city officials to close the artery linking Point Richmond housing developments and providing access to Miller/Knox Regional Shoreline.

"The structural engineer on Friday said this is a safety issue and (the tunnel) needs to be closed," City Manager Bill Lindsay said. "It's fortunate we discovered this during the repair rather than any catastrophic failure."

The closure occurred soon after workers for TPA Construction Inc., a contractor the city hired to shore up leaks in the tunnel and improve drainage, discovered an area on top of the inside of the tunnel that showed "significant concrete failure, which was causing large pieces of concrete to fall to the ground," according to a city news release.

Further inspection revealed a void 12 feet long by 10 feet wide and 4 feet deep above the concrete tunnel, which had thinned in places to as little as four inches thick and has no structural reinforcement, according to the release.

Lindsay said structural engineers from The Crosby Group assessed the site Friday and recommended a closure of more than three months, until April 30, while workers complete the original work and likely significant structural reinforcements.

The original tunnel repair project was $820,328, with $500,000 from a federal Department of Transportation grant and the rest from the city's general capital fund, according to council records.

"We have engineers on site this morning, but we have no cost estimate yet for the additional work," Lindsay said Monday. "Hopefully, we'll have something this week."

Work teams had been on the site since last month and had reduced the two-lane tunnel to one lane during construction. The tunnel links the commercial and residential areas of historic Point Richmond with the shoreline areas of Keller Beach Park and the Brickyard Cove and Seacliff neighborhoods.

The original project was repairing cracked areas of the tunnel lining, adding of carbon fiber strips to strengthen the lining and installing a new drainage system.

Councilman Tom Butt, who lives and works in Point Richmond, said the tunnel was burrowed through the hillside soon after the opening of the Panama Canal, as West Coast port cities rushed to upgrade infrastructure to benefit from the expected boon in shipping. Butt said he couldn't recall the last time maintenance work was done on the tunnel.

"Public agencies have a lousy record of maintaining infrastructure," Butt said. "Maybe that's the upside here, that we'll get this work done. It hurts while you're doing it, but at some point it has to happen."

During the closure, motorists and cyclists can access the areas via Washington Avenue to Western Drive or via Canal Boulevard and Seacliff Drive, which run through the Brickyard Cove and Seacliff neighborhoods.

Contact Robert Rogers at 510-262-2726 or rrogers@bayareanewsgroup.com and follow Twitter.com/roberthrogers.