ROCKLAND, Maine — Maine Department of Transportation crews began repairs Wednesday on “Maine’s largest pothole,” a 65-foot-deep sinkhole that opened on Old County Road last month.
DOT crews were set to relocate utility poles and clear trees and worked Wednesday to widen the hole, the first step toward repairing the road by the end of this month.
The road, which was built over a tunnel between two old limestone quarries, collapsed in the course of a few hours the afternoon of Feb. 15 when the supporting structure over the tunnel let go. The hole was 50 feet deep by that evening.
“We’re taking the remaining roof that hasn’t fallen in, then we’re going to start [filling] with large boulders at the base of the tunnel and into the quarry and build a good base and bring that above the water level,” said Mike Burns, DOT’s acting bureau director of maintenance and operations. “Then we will put gravel on top, up to the existing road.”
DOT’s public information officer Mark Latti explained Wednesday that the hole is shaped like an egg. The top of the hole, the part that is visible from the road, is the smallest width. The goal of the DOT’s excavation is to make the egg shape into more of a cylinder. This will ensure that all of the hollow, unstable parts are cleared before it is filled in.
The crews Wednesday pulled material out of the hole and took it to a nearby site. The next step is to fill the hole with rock and fill material.
The hole’s fill needs special consideration because groundwater flows in a tunnel that runs below Old County Road.
“We will start filling with stone,” said construction superintendent Randy Barrows. The stone will allow water to continue to flow through the underground tunnel. “Once we get above water level, we’ll reuse the material we pulled out,” he said.
DOT expects that once the hole is opened up, the crews will be filling a space 65 feet deep, 25 feet wide and 120 feet long. After the hole is filled in, asphalt will be placed over the road temporarily and the road will reopen.
Latti said the crews will pave the road in late spring or early summer, when the temperatures are more conducive to paving.
Latti said it will cost about $200,000 to repair the hole.
DOT is also investigating a second tunnel 100 feet from the sinkhole. Barrows said the radar detection DOT used earlier showed the second tunnel did not pose a threat to the road and was solid. Burns said his crews will investigate it more and have a definite conclusion by the time the road is opened.