There may be more large holes underneath the streets and roads of Council Bluffs besides the one discovered this week under Interstate 80.
But they likely aren't going to cause problems anytime soon, officials say.
“Things can happen … but there is no reason for us to believe we are about to experience a bunch of failures,” said Matt Cox, city engineer for Council Bluffs.
The eastbound lanes of I-80 near the 24th Street exit were shut down for about 12 hours after a construction crew installing a drainage pipe Wednesday night encountered a hole directly underneath the roadway.
The shoulder crumbled and the traffic lanes appeared imperiled, but they did not cave in.
A worker called 911, the Interstate was shut down, the roughly 12-foot-wide void was filled and then paved over with concrete, and the Interstate reopened Thursday morning.
On Friday, the Iowa Department of Transportation was still investigating what happened.
Officials are speaking with contractors KW Boring of Springfield, Neb., and Peterson Contractors of Reinbeck, Iowa, and hoping to come up with a protocol to keep Wednesday night's events from occurring again.
But whether the void was already there or created by the construction work hasn't been determined. Officials say it may have been there before Wednesday night.
Cox said such holes are generally created when the water table rises, forcing soil into older, leaky sewer pipes.
“As that continues to happen over time, a large void can occur,” said Cox.
The problem was widespread during the 2011 Missouri River floods, he said, when several Council Bluffs streets had to be closed and repaired.
Recent rains have added to the groundwater in the Council Bluffs area, but nothing like in 2011. That may have played a role in Wednesday's incident.
Dave Dorsett, the Department of Transportation construction engineer for the Council Bluffs area, described the soil around the hole as “a very sandy, noncohesive material that is prone to washing out.”
The soil conditions, along with the rains, likely played a role in the void being created, he said.
While there may be other voids out there, Cox said, motorists should not be concerned. Typically they are found and fixed long before they become a major problem.
“Most of the time there are small indications — you see a small dip in the pavement or something — before a catastrophic failure occurs,” he said.