(The following story by Eve Byron appeared on the Independent Record website on July 27, 2009.)
MISSOULA, Mont. — The removal of debris from a rockslide inside the Mullan Tunnel is progressing more slowly than anticipated, meaning that train traffic won’t resume on Montana Rail Link’s main line between Helena and Missoula until Friday at the earliest.
Last week, MRL spokeswoman Lynda Frost said that the company had hoped the tunnel would be reopened by today, but on Monday she noted that the project was a little more complicated than originally anticipated.
A July 20 rockslide near the middle of the 3,896-foot tunnel choked off the route; the 126-year-old tunnel, which is a vital east-west connecting route for MRL, is in the midst of an $18 million renovation.
“Initially, we had difficulties providing enough oxygen for the workers, so we needed to obtain some large fans to blow air into the tunnels,” Frost said. “There are multiple other issues. This is a long tunnel, with water in it sometimes.
“We have had various experts come in from across the country that are helping develop a plan to get this done as safely and as quickly as possible.”
One part of the new plan involves putting steel arches closer together than the original design calls for – about 3 feet apart, Frost said, adding that she doesn’t know what the original plan called for – and covering them with concrete. A steel plate also is affixed to the wall between the arches.
“They remove a portion of the rock before beginning to install the steel,” she said.
Frost added that eight sets of steel arches are in place, and workers will install more along 50 feet of the problem area. Crews are working two 12-hour shifts to move the work along as quickly as possible.
No one was injured in the massive rockslide last week, but the closure packed an economic punch to MRL.
Frost said she has no way to put a dollar value on the closure at this point, but noted that, not only does MRL have to cover the cost of removing the rockslide, the tunnel collapse also means that trains are getting backed up, and at least 1,500 cars have been rerouted at additional costs.
“It’s difficult to reroute and is a huge job,” Frost said. “I don’t think you can recover from these types of delays in one day, that’s for sure.”
The Mullan Tunnel, constructed in 1881 under the Continental Divide, is one of the longest in Montana and also one of the narrowest active tunnels in the nation.
At less than 13 feet wide, some trains clear it only by inches, and the newer engines have problems with oxygen in the tunnel.
The project will make the tunnel 5 feet taller and 3 feet wider.
Frost said crews were “mining” near the middle of the tunnel during the night on July 20, which involves removing rock to enlarge the tunnel, then shooting a type of concrete mixture known as shotcrete on the walls for stability.
Rocks started to tumble from the sides of the tunnel on their own in what’s known as a progressive failure.
The crews backed out of the tunnel, but tried to stop the rockslide by going in every few hours to shoot more shotcrete onto the walls. However, the efforts weren’t able to hold back the rock and the tunnel eventually was blocked.