Engineering challenges abound for routing highway across flooded Iron Range mine pit
VIRGINIA — The view on the drive across the new U.S. Highway 53 bridge over the Rouchleau mine pit lake would be spectacular, with green trees decorating the red-rock ore cliffs and the emerald green water shimmering some 200 feet below.
The bridge would be 2,800 feet long and 325 feet tall from the mine floor to the top of the arch.
One plan calls for a structure higher than the Blatnik Bridge in Duluth is above St. Louis Bay. The mine pit walls here are up to 325 feet high in places; the pit lake that has formed with groundwater seepage and rainfall is 300 feet deep in some spots.
“It would be the highest bridge in Minnesota,” said Pat Huston, an engineer for the Minnesota Department of Transportation’s Duluth district.But the height above the water isn’t what’s causing problems. It’s what’s down below that’s giving state highway engineers fits, and why the state is spending millions, more than $4 million this summer alone, just to see if a bridge even can be built here.Crews from Idea Drilling have two drill rigs on floating barges anchored in the Rochleau pit lake right now, drilling down through the water and into the mine bottom. But the mine, which produced rich natural ore from the 1920s into the 1970s, isn’t flat and hard on the bottom. Instead, mining crews dumped thousands of truckloads of unwanted rock into the pit, leaving rubble that varies from 40 to nearly 140 feet thick.“The material here is very challenging to drill,” said Marty Vadis, vice president of environmental affairs for Idea Drilling.The rubble ranges from marble-sized to the size of small cars, said Andy Johnson, assistant project manager of the Highway 53 re-routing. Below the rubble is the very hard iron ore formation at the bottom of the mine. Bridge supports will have to be drilled through the rubble and then 40 or 50 feet into the solid iron ore to make the bridge stable.Geologists with the University of Minnesota Duluth’s Natural Resources Research Institute are helping identify the difference between rubble and hard ore, and at what point in the drill-down that solid rock is reached.“It varies all along the routes,” Johnson said. “We relay don’t know how far down we have to go to reach a solid footing.”Later this month the state will award a contract to a construction company to erect and test several types of bridge supports in the mine pit to see which will work.MNDOT officials have called the re-routing the most geologically challenging project in the history of Minnesota road-making. If a bridge won’t work or is too expensive, other options call for millions of tons of rock to be dumped into the pit to make a land bridge across the middle of the pit, roughly following an old road used to haul iron ore out of the mine.Highway 53 must be re-routed because of a codicil in the 1960 deal between owners of the mineral rights under the highway, now RGGS, and the state. The deal allowed the state to build the highway but also gave the owners the right to kick the highway off with seven years' advance notice.They did just that in 2010, with Cliffs Natural Resources and RGGS saying they want to expand the Thunderbird Mine that provides taconite iron ore for Cliffs' United Taconite operations. If the taconite plant is to remain open well into the future, Cliffs says, it needs access to the ore that now lies beneath Highway 53.That notice set the clock ticking to May 1, 2017.“They say they’d be in there today if they could. They need that ore,” Johnson noted. “So there is a lot of urgency in all this.”The state has a half-dozen re-routing options that are viable on paper. But, as the News Tribune reported earlier this month, even if they find a single preferred route by the end of 2014, as is hoped, MNDOT officials concede they almost certainly will not meet the deadline.Meanwhile, as engineers test rock for routes, NRRI geologists also are helping MNDOT determine how much iron ore and other minerals may be under the new road routes. Whichever route is picked, MNDOT does not want to have to move the highway again in 50 or even 100 years because the ore underneath is needed.“There’s going to be some ore encumbered no matter which way we go. But we want this (re-routing) to be permanent,” Huston said.State officials say that money for the final route picked probably won’t be an issue, even if the final project is a budget-buster beyond the $90 million earmarked for the move. State lawmakers this year approved an extra $19.5 million from the state's construction bonding bill to pay for the re-routing of utilities — sewer, water and electric lines — that follow Highway 53, costs that otherwise may have been covered by local residents’ property taxes. That money also will pay to move the Mesabi Trail recreation trail.
Options remain for U.S. Highway 53, but none are easy
Officially, only one option for the re-routing of U.S. Highway 53 in Virginia has been discarded — to re-route the highway west of Eveleth and Virginia and back to its current alignment in Mountain Iron. Business owners along the existing highway protested loudly, and politicians were successful in getting the option killed early in the process.Several other options remain:
- No building. Essentially close the highway; that's not likely to happen.
- No new building. Instead, the state would try to "buy out" the rights to the iron ore below the highway, a prospect that could cost hundreds of millions of dollars and which mining officials say could close the entire United Taconite operation when it runs out of ore, putting hundreds of people out of work.
- The so-called M1 option to build the new road just west of the current alignment, right through the heart of the existing Thunderbird Mine operation's Auburn Pit. Cliffs has said it won't allow that option because of too many technical and regulatory hurdles and because it may hinder mine access. MnDOT still is studying the option, however, and conducting tests.
The most likely options include:
- The E1A bridge option, the most popular and direct but potentially the most challenging route over the Rouchleau mine pit that would link back with the existing highway alignment near the Virginia Target store.
- The E1A fill option, which would fill in part of the open-pit mine and route the new highway on fill rather than a bridge, following along an old road used to move ore out of the mine. A sub-option has the fill encased in concrete, looking much like a dam.
- The E2 option to cross the same mine pit but farther north, taking longer loop to meet back up with the existing highway alignment, still near the Target store.