Devils Lake in North Dakota has one outlet for the water to flow. During heavy snowmelt in spring and wet cyclical weather, the water level rises and spreads outward with various levels of flooding to surrounding areas because the outlet is higher than the roadways. For at least the past five years, this situation prompted residents to move and, since 1994, the DOT has been raising roadways and building embankments to hold back the water.
In 2010, Devils Lake rose to a point where some roads were covered with water. To keep traffic moving in the city and beyond, a team from the North Dakota Department of Transportation, Federal Highway Administration, and engineering consultants Kadramas Lee & Jackson met to plan reconstruction of state highways 20 and 57, major roads for residents to get in and out of the city.
Bonnie Greenleaf, project manager, U. S. Army Corps of Engineers in the St. Paul district, said the team tested the soil at the existing Highway 20. “We found out the soils were worse than we expected, then we took more samples and decided to redesign the road.” The team knew an embankment must be built to act as a dam and Highway 20 had to be raised to keep it above water.
Protection for the city
“We wanted the embankment to be a continuous protection around the city, and the road has to ramp up and over the embankment,” said Greenleaf. “It’s a state highway, and the DOT wants to keep it open to traffic during construction.” Paul Lee, Kadramas Lee & Jackson, said, “This road has been raised at least three times in the last 10 years, and I’m sure there were raises beyond 10 years ago because Devils Lake has risen 30 feet since the early 1990s.”
The current road design went through a few independent reviews from other agencies, as Congress had mandated, to make sure it
met all federal criteria and appropriate steps.
Ames Construction Inc., Burnsville, Minn. received the contract and, in July, began removing asphalt from part of Highway 20, then graded the area. Ben Lovin, project manager, said his team hauled impervious clay material from borrow pits around Devils Lake as fill to raise the grade. “Highways 20 and 57 intersect in the lake and run jointly along the lake. On portions of this project, we’re raising the grade to reconstruct the road to a higher elevation on both highways. We continue to fill over the top of the existing road until the road is at the correct elevation.
Roadway shifted
“The center line on the highway shifted slightly, but we were able to construct a portion of the new road while keeping traffic moving on the existing pavement. We’ll have to move traffic onto a temporary bypass when we remove the existing pavement and finish the earthwork to build the grade on the other side,” said Lovin.
The affected section of the road is 5.7 miles, and Ames Construction workers are raising the road by about five feet and widening each highway. “We have to compact it with every lift of soil because compaction is integral to the earthwork,” said Lovin.
Workers continue with soil lifts and compaction while the dam also is under construction. “The dam is the road, and cars will drive on top of it. You won’t see the difference between the grade raise portion and the dam portion of the highway,” said Lovin. “The whole point of this road is to hold back the water.” This year, Devils Lake is deeper and
required more soil to raise the grade.
When the road base is built to the proper width, workers will determine and build the slope on both sides of the road. Gravel and asphalt will complete the road surface.
By engineering calculations, Lee said Devils Lake is at 1,458 feet, but spreading. “The road is in the water now as the lake spreads and is about three feet above water.
Inspection for dam
“There’s a section of the highway that doesn’t go through the lake. It goes along the shore, and that’s the part of the road we’re keeping out of the shore. We have to dig an inspection trench and perform geotechnical design on this portion, which is the dam. We’ll install a sand blanket, a chimney drain and a drainage system that catches any water that migrates into the structure,” Lee explained.
Currently, Ames is excavating a considerable amount of dirt to remove unsuitable soils under the dam base. Greenleaf said, “Normally, with a dam or reservoir construction, the contractor would pull down the water and keep it at the lowest tolerable elevation to avoid working with water pressure on the other side of the dam. On this project, we don’t have a way to pull down the water; we’re working under full load and that’s a challenge.”
Impervious clay, brought in from area clay pits, will replace unsuitable soils except in the area of the sand drain. Riprap will be placed on the lake side of the dam with a smaller amount of riprap on the shore side. A pump will be placed near the drain structure to pump away water.
Equipment on site
Ames brought about 150 pieces of equipment and trucks to Devils Lake for the various projects in and around the area to work almost 24 hours a day for six days a week, according to Lovin.
“Our winter shutdown was from December through the end of April,” he said, referring to North Dakota’s short construction season. Lovin expects to complete raising grade levels this summer and paving the highways with asphalt by September.
The U.S. Army Corps of Engineers helped raise the Devils Lake embankment in 1996 and in a few subsequent years. Some Corps employees are at the site to oversee contract administration and check quality control. Greenleaf said Ames manages the elaborate traffic control on the highways to keep one lane open at all times.
North Dakota DOT engineer Wayde Swenson said the project costs $56.6 million, is the largest construction project ever bid in North Dakota, and includes: 300,000 cubic yards of common excavation, 2.6 million cubic yards of borrow, 300,000 tons of riprap, 130,000 tons of bedding stone, 130,000 tons of sand and 1.4 million cubic yards of impervious core material. The project is expected to be finished in November 2011.
