Plans for Highway 67 reroute are announced
Last week, a meeting was held in Granite Falls for the Friends of Upper Sioux Agency State Park with Cody Brand, Project Manager for MnDOT out of District 8. Brand was in attendance to provide information on plans MnDOT has for how to handle the thousand-foot failure on Highway 67 that runs through the State Park near the Visitor’s Center. A portion of the highway has been closed for a couple of years after a large crack formed on the road’s surface, with a portion of the road sinking to create a six-inch separation in the pavement. Brand began the presentation by identifying two geotechnical issues along Hwy 67 that MnDOT has been studying.
The first is a large slope failure near where the Yellow Medicine River approaches the roadway. Brand showed photographs taken over a period of time beginning in April of 2019 when the road was first closed down due to the separation. Just a month later, the six-inch separation grew to show two and a half feet of movement on the surface of the roadway. In May of 2020, the pavement dropped three feet, and additional tearing showed up in other areas about a thousand feet from the original separation. Brand explained that the deterioration on the roadway surface has much to do with the deterioration of the riverbank along the Yellow Medicine River. “There’s visible distress. You can see the bank is sloughing away,” Brand said. “This has been very problematic for years now, and some of the scarps you see in the river bank are over two feet in height. We continue to lose more and more material in the river bank and ultimately, that’s destabilizing the top of the hillside where the roadway is.”
Brand showed graphs of data collected from equipment installed in 2019 to monitor movement in the hillside. “We’re seeing a lot of movement along the entire hillside. We installed instrumentation called slope inclinometers, and they read how much movement is occurring in the hillside. We’re detecting movement at a couple of different depths.” In one area of the thousand-foot stretch of Highway 67 that is showing surface damage, the movement was detected at a 46-foot depth, while in another it was at a 32-foot depth. “You can kind of draw a line between these instrumentations and you can see that movement correlates with the bottom of the riverbank,” Brand said. The data also shows that the movement is occurring not only at a great depth and consistently over time, but that the land is moving as one mass. “What we’ve been experiencing in 2021 is that the movement has slowed down significantly, and that is very likely due to the lack of rain this year. 2019 was extremely wet. We had large snowfalls, large melt and we had a lot of riverbank erosion and groundwater. It is very unpredictable to say whether or not this trend will continue. It really largely depends on what we have for weather the next couple of years,” says Brand.
Highway 67 has been in place for approximately 80 years in its current alignment, and Brand says that there was no movement observed in that time on the surface. “There may have been smaller amounts of movement that were kind of covered up every time we resurfaced the roadway, but nothing on this scale. It can be kind of unpredictable and move at any time,” he said.
The second geotechnical issue MnDOT has identified is at the Yellow Medicine River Bridge just a short distance down Highway 67 from the road failure. “Some of the more serious issues are that the Southeast end of the bridge is continuing to push to the Northwest. The hillside is pushing toward the river. The hillside moving is pushing the end of the bridge into the bridge deck,” he said. Brand explained that the bridge is designed in such a way that a deck is supported by an abutment that works as a shelf. The deck is connected to the bridge beams and those beams sit on the abutment. The abutment consists of piles that go into the ground and support the beams. “Each of those elements acts independently. The bridge deck can float on those shelves in order to allow for expansion and retraction for the seasons,” Brand said. “What we have on each end of the bridge is what’s called an expansion gap. An approximate four-inch gap between the abutment and the bridge allows that movement to happen. We have seen that completely close up over a ten-year period. Our maintenance forces went out there and cut out a portion of this deck to reestablish this expansion joint, and it’s pretty much closed up again since 2018. Four inches of movement at the surface in a three-year period, so we’re seeing that this movement is beginning to increase exponentially.” Brand also explained that the previous measure of cutting a portion of the bridge out to create a new expansion joint would not be a possibility for the future, as the previous work done has left no room to allow for a second cutting. “Relative to the roadway failure, this is a lot less movement but it still does translate to a lot of movement at the surface,” Brand said.
With explanations of the issues on Highway 67 out of the way, Brand moved on to present the solutions that MnDOT has explored while deciding what to do with Highway 67. “It really came down to that there are three alternatives for this area. The first option was to reroute Highway 67 and we considered two routes, both using Highway 23 coming South out of Granite Falls, Highway 274 continuing South towards Wood Lake. One of those then utilized County Road 18 approximately three miles North of Wood Lake, the other is similar but uses County Road 2 just on the North side of Wood Lake,” he said. That option, Brand said, is projected to cost between $12 and $14 million.
Another alternative measure considered was reconstructing Highway 67 through the park and replacing the bridge, moving the roadway off of the current alignment to some other point in the State Park boundary. “Where we are experiencing our issues is between the Yellow Medicine River and the Minnesota River. We don’t have a whole lot of land to work with there for choosing an alternate route. Our roadway on both sides is adjacent to State Park property. We considered bringing the roadway further along the bluff on the North side of the current roadway and then bringing it back down the bluff at some point to the East of the current failure and trying to avoid that current failure zone. With that we would also have to replace the Yellow Medicine River bridge because of the instabilities there,” Brand said. This option is projected to cost between $22 and $30 million.
The other option considered, which was also the most expensive option considered at a cost of between $38 million to $45 million, was to reconstruct Highway 67 in place along its current alignment and replace the bridge. “We considered the highway user impact, the initial cost for each of the alternatives, the environmental impacts, landowner impacts, future maintenance costs for each of these alternatives. There’s certainly other factors that go into our decision-making, but these are the ways we can categorize the different impacts,” Brand said.
It was determined by MnDOT after having experts from around the country and some global companies review all of the data that the option that presented the best-case scenario both financially and being conscious of environmental and cultural impacts, would be to reroute Highway 67. “What we came up with with our final determination is that highway 67 is going to be rerouted onto Hwy 23, Hwy 274, and County Road 2 just North of Wood Lake. Highway 67 is going to terminate with a cul-de-sac near the park boundary, and then existing Hwy 78 in the park will be vacated and turned over to the DNR as they own the land for that corridor,” he said. The current portion of Highway 67 from Hwy 23 to the Upper Sioux Agency State Park main entrance will be redesigned as a trunk highway. The portion of Highway 67 South of the failure where the Yellow Medicine River Bridge is will remain in service for approximately five years. “The estimated remaining service life of the bridge is approximately five years, so it will be left in service and we will continue to monitor the movement of that bridge to determine whether that’s accelerating or slowing down and we’ll adjust accordingly,” says Brand. That portion of the road containing the bridge will be turned over to Yellow Medicine County to become a County Road. “We are working on the details with the County for them taking over that portion of the roadway. We will be entering into a turn-back agreement with them, so they will take over that property from Yellow Medicine River Bridge all the way to County Road 2 and then County Road 2 will be the new Highway 67 and continue from that point to Echo,” Brand concluded.