Overweight loads damage Dalton Mountain Bridge

A semi-annual inspection of the Dalton Mountain Road Bridge by the Montana Department of Transportation in September revealed considerable damage to piles reinforced by Lewis and Clark County in 2017.

County Engineer Dan Karlin said the damage to the piles is the result of loads that exceed the 10-ton weight limit crossing the bridge.

"The bottom line is we really need that to stop," he said. "That is contributing to this. If it continues, based on conversations with MDT and the (bridge) conditions, they may have to close this bridge until its replaced."

The Dalton Bridge has been limited to one-lane traffic for the past four years after an inspection revealed that the bridge's aging timber piles had deteriorated to the point that the structure was no longer safe.

The county repaired four of the piles in 2017, wrapping them in FX-70, a hi-tensile fiberglass structural repair system often used for bridge pile repair projects. Karlin said in August of this year the county completed reinforcements on three more piles to help ensure the bridge would remain open to traffic until it's replaced by the state under the MDT's Off-System Bridge Replacement Program.

Karlin said MDT discovered that two of the FX-70 wraps installed in 2017 had burst.

"That is really rare," he said, adding that out of thousands of such repairs, only a handful have ever done that.

The state reported the damage to the county in a written report, but Karlin said the red flags that prompted a closer look into the cause of the damage came when they met the state bridge inspector at a different project and saw photos of the damage.

The county has received reports that overweight loads were using the bridge, rather than taking the detour around Herrin Lakes Road and he said they have had conversations with locals in the area.

In addition to the bridge's importance to residents in the Willow Creek and Dalton Mountain areas, Lincoln Fire Chief Zach Muse said the bridge is closed, emergency services such as the fire department and the ambulance will be forced to use the Herrin Lake detour, which will add several crucial minutes to their response times.

MDT is still planning on a 2023 date to replace the bridge, but Karlin said they need the help of locals to keep the bridge in operation until then.

"If you are doing it, or if you know who's doing it, have a cordial conversation, or please stop," he said.

To help make sure vehicles aren't exceeding the weight limit, the county has installed video surveillance of the bridge.

Karlin said the county is planning to repair the piles with burst wrappings by encasing them in a welded steel sheath, a process that's expensive and involved.

"We can't spend the money to wrap every one of (the piles). It's just too much for something that's getting replaced hopefully in a year and a half."

Karlin doesn't have a date for the upcoming work but said they may have to close the bridge temporarily while the repairs are made.

Due to the new damage, Karlin said MDT will put the bridge on a three-month inspections cycle, instead of the current six-month cycle.He said the standard inspection cycle is two years.

The Montana Department of Transportation has scheduled a community meeting at the Lincoln Library Community Room Nov. 18, from 4 - 7 p.m. to discuss the Dalton Mountain Bridge replacement.