PROJECT
U.S. Highway 12 Bridges
at Mileposts 17.3, 19.6, and 19.8
Three replacement bridges on the Lewis & Clark Highway
by Jim Scoles, Morrison-Maierle Inc. and Kent Barnes, Montana Department of Transportation
In July 1805, the Lewis and Clark expedition passed by the confluence of Deep Creek and the Missouri River in what is now Broadwater County, Mont. Less than two river miles upstream, William Clark mapped the area as “Yorks 8 Islands,” and Meriwether Lewis noted the beavers’ role in creating the islands. The mouth of the steep, rocky canyon through the Big Belt Mountains lies 12 miles due east as the raven flies.
The Lewis & Clark Highway—also known as U.S. Highway 12—runs along the narrow floor of Deep Creek Canyon. The 24-ft-wide, two-lane highway between Townsend and White Sulphur Springs was constructed in the 1930s with timber bridges at eight locations where the creek and the highway intersect. High flows during spring runoff in 2011 resulted in significant scour of the bridges and severe erosion of the highway embankment. The flooding required emergency response to prevent structural loss and ultimately triggered a project to replace the bridges in this rural area of southwestern Montana.
In the first phase of the project, the Montana Department of Transportation (MDT) replaced three timber bridges with new 54-ft-long, single-span, precast concrete structures using accelerated bridge construction (ABC) techniques. Initially, even with ABC, complete road closures were not considered an option because of the required two-hour, 120-mile detour around the Big Belt and Bridger mountain ranges.
Profile
U.S. HIGHWAY 12 BRIDGES AT MILEPOSTS 17.3, 19.6, AND 19.8 / BROADWATER COUNTY, MONTANA
BRIDGE DESIGN ENGINEER: Morrison-Maierle Inc., Helena, Mont.
PRIME CONTRACTOR: Dick Anderson Construction, Helena, Mont.
PRECASTER: Oldcastle Precast, Spokane, Wash.—a PCI-certified producer
GEOTECHNICAL CONSULTANT: SK Geotechnical, Billings, Mont.
