Lots of grout used on rehab project

Loose sedimentary rock and a mandate to maintain historical authenticity posed difficult challenges to engineers working on the Going-to-the-Sun Road rehabilitation project. That was on top of the extreme weather, short work season and heavy summer tourist traffic that contractors faced on the alpine section of Glacier National Park’s popular thoroughfare.

Two men familiar with these challenges, Glacier Park landscape architect Jack Gordon and Federal Highway Administration engineer Michael Baron, described challenges and solutions in a talk to the Columbia Falls Area Chamber of Commerce on March 12.

In terms of tourist dollars, some argue the Sun Road is the most important attraction in Montana. Engineers and contractors were told to keep the traffic flowing while thousands of tourist vehicles snaked up the highway to Logan Pass. That meant finding narrow guardwall designs that didn’t block the road and keeping delays down to 20 or 30 minutes.

“Contractors sometimes could only work 20 minutes per hour when grading,” Baron said.

A major downpour last July, which dropped 1 1/2 inches of rain along the Garden Wall, sent 600 cubic yards of rock and gravel down on the Sun Road at Siyeh Bend. But instead of hauling it out, Gordon said, the contractors filled in steep drop-offs adjacent to the highway, creating places for visitors to stand and enjoy the views.

Providing stone that matched the historical masonry proved to be a major hurdle, Gordon said. At one point, cast concrete walls with simulated stone was proposed for the guardrails, he said. In the end, Flathead-based Anderson Masonry established four quarries, as far away as Thompson Falls, to provide the needed rock. Heavy equipment was used to preshape the stones before delivery.

Masons also figured out a way to saw faux joints in rocks that were otherwise too large to use. Crumbling mortar joints were repointed, and powerwashing removed decades-old grime, exposing the rich colors of red rock used to face bridge and culvert masonry. In places, backfilling will cover rock that doesn’t match the historical masonry.

Slope stabilization and rock fall have been an issue on the Sun Road for years, Baron said. The problem was exacerbated by improper blasting in the past that further fractured cliff faces. Cracks filled with water and froze in winter, causing cracks to expand, further weakening the sedimentary rock.

“Gluing together” the Garden Wall’s loose rock required a lot of drilling and grouting. About 6,000 feet of six-inch diameter compacted-grout columns, 8-25 feet deep, were installed along the alpine section, Baron said. Engineers utilized shotcrete — concrete or mortar sprayed over rock faces — after learning about architectural-grade shotcrete used in zoos that matched the color of native rock. About 5,900 feet of rock bolts also were installed, especially at Triple Arches, Baron said.

The roadway was improved with about 24,000 cubic yards of subgrade excavation. Drainage was improved with gutters placed along the shoulder and wider culverts. About 5,000 feet of new culverts were installed, many faced with matching masonry work.

Gordon noted that following controversial crash wall tests in the 1980s, engineers came up with several solutions for guardwalls along the narrow alpine section. In some places, hollow masonry walls were filled with rebar and concrete. Altogether, about 11,000 feet of new guardwall was installed.

Removable timber rails are used where avalanches rip up expensive masonry walls. Gordon said 5,000 feet of new timber rail was installed, including replacing green-treated railing with a new half-log design that’s painted brown. In some places, metal I-beams supporting the removable rails sit on flexible neoprene footings intended to absorb the impact of avalanches.

“That design took 12 years to develop,” Gordon said.

Improving visitor experience was also part of the project. Work at pullouts along the Sun Road that Gordon called “crowsnest sites” included building a handicapped-accessible trail and steps to existing “social trails” at Lunch Creek. A grant from the Glacier National Park Conservancy will be used to improve a trail at the popular Red Rocks pullout along McDonald Creek this summer, Gordon said.