The 20 by 20 sinkhole on Father Hurley Boulevard was caused by the failure of a 38-year-old culvert pipe which had rusted out, according to County officials.
The sinkhole is expected to close traffic on one of Germantown’s most important north-south thoroughfares for a few days, but more bad weather may extend the time the road is closed, said Bruce Johnston, Chief of the Division of Transportation Engineering for the Montgomery County Department of Transportation.
“We want to reopen it to traffic as quickly as we can,” said Johnston, “but we want to reopen the road only when it is safe to do so.”
Johnston explained that the sinkhole was the result of the massive amounts of rain coupled with an aging piece of infrastructure which Montgomery County didn’t even know was there until January of this year.
“This pipe, which is a corrugated metal pipe, was installed about 38 years ago,” said Johnson. “To be honest with you, we didn’t even know it was there until about January. It was built by a developer in the early 1980s, and it was never put onto our inventory of bridges and culverts. When we did find out it was there, we did an inspection of it.”
The inspection identified the rotting pipe and, according to Johnston, the County was in the process of planning the replace the pipe, “however, we couldn’t get it done before the storm hit last weekend.”
“The pipe is made of corrugated metal and after 30 years the areas where these pipes have water running along the bottom of the pipe – even though it was galvanized it does get rusty along that portion of the pipe,” explained Johnston. “It gets so rusty, that it rusts out completely and there is no more metal on the bottom of the pipe. When that happens, the soil pressure around this pipe which is 25 feet deep below the roadway and the pressure causes it to curl up into a smaller pipe, which is what has happened in this case.”
The smaller pipe can’t handle the excess water, which the area experienced this weekend. “There has been so much water going through and around the small pipe, the soil around erodes, and in this case, it eroded upwards towards the roadway and the soil gets washed away over a number of years. Finally, this big storm created so much water and energy it caused a lot of soil above to fall down into that hole and it created a sinkhole caused by all the rainwater.”
Once the sinkhole was identified, Montgomery County Highways Services crews began filling it with gravel.
“They put lots of gravel into the sinkhole to get it back up to the surface. What we plan to do is pour, what is called ‘flowable fill,’ which is a very thin concrete that will flow in and around that gravel and plug that hole up. And once that is done, over the next couple of days we will be able to get traffic back on the southbound lanes,” said Johnston.
The sinkhole itself only seems to affect the southbound lanes, but the entire roadway must be closed because the damaged culvert runs under the roadway allowing for water to runoff.
“Then we will need to do work on the northbound lanes,” he explained. Johnson said that on Monday, his crews ran a camera up into the damaged culvert, which is a 55-to 60-inch pipe. “We don’t want to put people in there because we don’t think that it is safe, however, if it looks like it is sound and secure, we may be able to open up the northbound lanes as well.”
He cautioned that the process could be hampered by the weather. The National Weather Service has forecast heavy rain for Tuesday and Wednesday of this week and a Flash Flood Watch has been issued for Germantown through late Tuesday night.
“In terms of getting the road back open to traffic, I am hopeful – of course, we have some bad weather expected every day for the next three or four days we are forecast to have thunderstorms again so that will be a factor. If all goes well, we are hoping to have the roads open to four lanes of traffic again mid- to late this week,” said Johnson.
Residents can expect to see County work crews at the site long after the roadway is opened for traffic as the process for replacing the damaged corrugated metal pipe has been moved accelerated by the appearance of the sinkhole.
“We are pumping water from the drainage area into a diversion which will take the water into another area. In the long-term, we are going to construct a complete replacement for this pipe. It will be somewhat parallel to the corrugated metal pipe that has failed, but it will be slightly off to one side,” said Johnston.
Johnston said that County officials met with a contractor Monday morning regarding the replacement for the failed culvert. He said that once the stop-gap measures to secure the roadway are completed, and all lanes are open to traffic, the County would begin the process of a permanent fix for the area. However, the permanent fix would not include a long-term shut down of Father Hurley Boulevard.
“It would be a disaster to shut down that road and do what we call an open cut because there are utilities in the road that we’d have to deal with,” said Johnston. “So, what we will do is install a new pipe in a process we call ‘Boring and Jacking.’ We’ll have an excavated pit alongside the road, and we will get down in that hole at the right elevation, and we will push a series of pipes through dirt, underneath the roadway to get to the other side. We will not have to close the roadway down again after we get it stabilized.”
He said that Boring and Jacking process is an expensive operation, but “we fell that it is worth it to keep the roadway open. It will take some time, and it will be ongoing for the next couple of months.”
Photos by Germantown Pulse.