By Roz Kohls
The road failure of Meeker County State Aid Highway 18, south of Dassel, has County Highway Engineer Ron Mortensen baffled, he told the county board of commissioners Tuesday.
There doesn’t seem to be enough water in the four affected areas within the 7.5 mile resurfacing project to have caused at least $200,000 in damage, so far. At the same time, the oil, bituminous, operations, and roadbed have passed every test engineers, MnDOT, and materials experts have done on the $2.2 million project, Mortensen said.
It appears the road slid off its bed, causing cracks, some as long as a yard, in 25 percent of the second layer of bituminous. The contractor, Knife River of Sauk Rapids, discovered the failure Aug. 28.
The damaged areas were on the tops or sides of hills, not low areas. The Dassel area had less than average rainfall this summer, so it isn’t rainwater that caused the roadbed to move. The contractor surmised it might be from underground springs.
The most recent test was done on the strength of the roadbed. Mortensen first received the results early Tuesday morning. The tester used a machine with sensors that measured down through the bituminous, clay, gravel and dirt in the road every 500 feet, or in about 40 locations in the 7.5 miles resurfaced, Mortensen said.
The results were posted as a line graph. The top line showed the strength of the road in terms of inches of gravel. The more inches of gravel, the more strength the road has. A road the size of CSAH 18 is supposed to have the strength of 18 to 20 inches of gravel, he explained.
However, the four miles with 60 percent of the road failure show the strength of 20 inches of gravel or more. There is only one location out of 40 that is weak, and it is in the seventh mile, Mortensen said.
MnDOT engineers said they thought the damage was from weak subgrade, but this latest test of strength shows they were wrong, said County Administrator Paul Virnig.
Density tests also show the roadbed is not the problem. Density is supposed to be 91 percent at least, and CSAH 18 is between 92 to 96 percent, Mortensen added.
Nothing in the tests so far, shows what is causing the problem. Everything is within normal range, he said.
The oil will be retested, however, so the testers have a larger quantity to test, Mortensen added.
Another possibility is the 80,000-pound construction semi trucks that drove on the new surface within hours of when it was put down, Mortensen said. There is no direct evidence, however, the trucks caused the road to move either, he said.
Knife River has replaced the defective 1.5-inch layer of bituminous with another layer. As of Tuesday, the replacement layer is holding. However, Virnig said he is nervous, because the replacement layer is the same material as the original.
Mortensen and other engineers were at the site, every day, all day, when the replacement layer was done, watching how the operators put down the bituminous. Some engineers walked next to the paver for a close-up view as it moved down the road. No one noticed anything that was done incorrectly, Mortensen said.
A final 1.5-inch layer of bituminous is scheduled to be placed beginning Monday, Oct. 13.
Mortensen asked the board if it wanted to spend an extra $210,000 to tile both sides of the 7.5 miles of CSAH 18 and drain away any water, but none of the commissioners responded.
Commissioner Ron Kutzke was reluctant to have the final layer of bituminous added without knowing what was wrong with the road, he said.
Mortensen said most damage to roads happens in the spring, so it is best to make the road as strong as possible before then.
In other highway business, the board awarded the five-year highway construction bond bid to UMB Bank, N.A. of Kansas City, Mo., for $2,988,000 at 2.83 percent interest.
The board also awarded the contract to replace the Cedar Mills Township bridge at CSAH 12 to the low bidder, Landwehr Construction of St. Cloud, for $61,130. The township will contribute $6,936, and the state will pay the rest.
Odds and ends
In other business, the county board:
• certified to the county auditor the 2009 levy of $11,141,722, a 7.8 percent increase over the 2008 levy.
• purchased property at 308 N. Ramsey, Litchfield, for parking spaces for the courthouse for $42,000.
• approved a building code enforcement agreement with Darwin.
• scheduled the county auction for Thursday, Oct. 16 at 4:30 p.m. in the impound lot next to the wastewater treatment center in Litchfield. Brad Dahlman will be auctioneer.