The tools are available to find areas where roads may collapse into sinkholes, but not the money.
As a result, sinkholes such as the one in Milwaukee on Thursday that swallowed a utility truck will remain an inevitable part of modern civilization, said Alex Barker, president of River Valley Testing Corp., a Neenah-based consultant that studies underground conditions for street and building projects.
The sinkhole Thursday on 27th Street in Milwaukee occurred because a water main that broke in March washed away the soil beneath the pavement, leaving a void and causing the street to crumble when a We Energies truck stopped at a traffic signal.
“With a water main break, you get a lot of water main breaks in a given year, so I think it’s just a part of developing our society,” Barker said. “And those things are going to happen, and I don’t know how much you can do to prevent that.”
Technology exists to detect voids below city streets, but the city only performs the scans before road projects, said Dale Mejaki, Milwaukee Department of Public Works field operations manager. Scanning all 2,000 miles of Milwaukee’s streets would be too costly, he said, and the data would become outdated as underground soil shifts.
Barker said it costs about $10,000 to $15,000 per day to perform the underground scans.
On 27th Street, the underground void occurred south of the water main break, and crews that fixed the break did not realize that water had flowed down to create the void, Mejaki said. That segment of road was to be rebuilt this summer, he said, and crews would have discovered the void during the project and fixed it.
“We will discover those as we go in and do excavations,” he said, “and we do go in and open up the streets lots of times.”
City crews finished filling the sinkhole with concrete on Friday, Mejaki said, and will pave over the road.
Mejaki said the city does not keep records of sinkholes, so he cannot say how often they have occurred. In February 2009, the city closed Locust Street after the street collapsed into a sinkhole. The void was caused by the collapse of a 21-inch diameter pipe.
“It’s difficult to predict when this kind of thing is going to happen unless you see something happening or you hear the water rushing,” said Bruce Brown, senior geologist for the Wisconsin Geological Survey.
Barker said it is increasingly common for Wisconsin municipalities and developers to test soils before building to see if conditions are favorable for sinkholes. Wisconsin wind farms, for example, require tests to see if the bedrock underneath a wind turbine site could give way and cause the ground to collapse.
“Some things that may have been passed off as an anomaly in the past,” he said, “some people are starting to realize they are a little more common.”
But scanning roads to search for voids and prevent sinkholes has not caught on, Barker said.
“If you throw enough money at any problem, you can solve it,” he said. “But in this day and age, you have to balance the cost.”