A massive “sinkhole” at least 4 feet deep and up to 190 feet long has created a “void” under the Interstate 90 connector tunnel in the problem-plagued Big Dig, adding to a growing list of engineering failures that include a deadly ceiling collapse, dangerously unstable light fixtures and lethal railings, state transportation officials revealed yesterday.

Transportation officials insist there is no risk of a new catastrophic collapse in the tunnel — the same one where Milena Del Valle was killed by a 3-ton slab of concrete five years ago — but some critics said they aren’t convinced.

“You hear this and think, ‘What’s coming next?’ ” asked Rep. Peter Durant (R-Spencer), a Transportation Committee member calling for a probe of the latest Big Dig fiasco. “This is just another in a long line of problems for this project.”

The gap 9 feet under the tunnel’s roadway, filled with water and resembling a subterranean pond, was caused by an unexpected degree of settling of the clay soil around the tunnel as a result of a pioneering technique called “ground freezing” while contractors dug under the train tracks serving South Station.

“It’s the settling of the dirt, so it’s a sinkhole,” Frank DePaola, acting highway administrator for MassDOT, told the Herald.

But he and Richard Davey, Gov. Deval Patrick’s newly appointed transportation secretary, insisted the tunnel is safe.

“We would not be letting cars go through there, or more specifically trains over those tracks, if there were any issues whatsoever,” Davey said.

DePaola said he outlined the problem, discovered four years ago, to the MassDOT board yesterday because in his new job he is evaluating all the Big Dig issues and wants to share them with the public.

The state expects to spend at least $15 million to repair the problem by drilling the area and filling it with concrete, once the ground finishes settling by 2014. It already has

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