The Montgomery County sinkhole near Gaithersburg, Maryland, that continues to frustrate drivers and muck up traffic on southbound Interstate 270 is 20 feet deep and 30 feet wide under the roadway, state highway officials said Friday.
Maryland State Highway Administration spokesman Charlie Gischlar told WTOP “a 30-inch corrugated metal drainage pipe” under the roadway was the problem.
“There is a lot of damage underneath there,” Gischlar said, noting that the storms that pop up across the D.C. area in the summer can drop 1 to 2 inches of rain an hour and create “a lot of moving, high-velocity water” that eats away at the soil near where the pipe failed.
A 1,000-foot jersey wall will have to go up while fixes are being worked on, he said, followed by a safety mechanism “for workers to get in and start working in that unstable area. So work is actually starting to commence,” Gischlar said.
The sinkhole extends underneath the lanes in the roadway.
“So it is very extensive underneath that roadway there. That’s why we had to close those two right lanes,” Gischlar said.
“We’re gonna have to go in there and fix the pipe, first and foremost, but then put in the No. 57 stone and the soil and compact it, make sure it’s stable enough. Then we can open up the lanes.”
He added that there are too many unknowns right now to give an estimate on when work would be complete.
“The great news is that we’re starting to work. But what often happens is we’ll find something else underneath there which could extend the closure of the lanes,” Gischlar said.
“I can’t really put a tag on it right now. I don’t want to build hopes up and I don’t want to be doom and gloom either,” Gischlar said. “I just want to make sure that we get the work started that will make everybody feel better, including us.”
Below is a map of the area of the site.