After more than six years of costly, innovative and challenging work, Glacier National Park is closing in on the conclusion of a comprehensive rehabilitation project on Going-to-the-Sun Road.

It’s a project of such magnitude that its planning stretches back to the late 1990s, when a citizens advisory committee was appointed by the Secretary of Interior to figure out how to save the historic alpine highway that was showing obvious signs of wear.

When a huge chunk of the road slumped near the West Tunnel in 1995, it got the attention of then-Superintendent Dave Mihalic, who was concerned that the road could catastrophically close itself some day. A priority for the park was born.

But actual work didn’t get underway in earnest until 2007.

Since then, the Federal Highway Administration and the park have spent nearly $135 million on the road, a price that can largely be attributed to the difficult nature of the road job — four-month work seasons, unpredictable harsh weather, falling rocks, avalanches, debris slides and the necessity to work in ways that allow visitors to continue using the road.

And every year presents new challenges.

“It’s a shell game. Every spring you go up on that road and there’s new damage. It takes a beating,” Glacier landscape architect Jack Gordon said during a presentation on the Sun Road project Wednesday in Kalispell with Federal Highway Administration engineer Mike Baron.

Because of the project’s unpredictable nature, Gordon said it’s estimated that roughly $20 million is needed to “have this road really shiny at the end of this rehab.”

The remaining work is mainly paving and improvements on low-elevation segments of the road. This summer, there will be two work zones — between Logan Pit and Avalanche on the west side of the park and between Siyeh Bend and Rising Sun on the east side.

“We’re on the home stretch, but we’re having difficulty right now with forecasted available funding to complete it the way we would like to,” Gordon said.

The daunting, heavy-duty work on the alpine segment has been finished, an accomplishment that park officials had doubts about before the work began.

“We questioned whether we would get the alpine section done with the amount of money we were getting allocated,” said Gordon, noting that additional funding obtained by Sen. Max Baucus and federal stimulus money made up the difference. And the project ended up within the original estimated range of $140 million to $170 million.

Gordon and Baron provided a glimpse of what the work has entailed.

Subgrade stabilization involved the excavation of 24,000 cubic yards of material from the old road bed and an equal amount of material to rebuild the road.

“It’s been a challenge trying to minimize the amount of material” that needed to be moved, Baron said.

Pressurized grout was injected into vertical columns to reinforce some of deeper unstable areas.

Installing larger culverts and concrete box culverts was another major part of the project.

“It’s been a big focus of ours, to improve the drainage on the road,” Gordon said.

Stone masonry work accounted for about 20 to 30 percent of the project’s cost and time. The park salvaged rock from above and below the road but also relied on four quarries outside the park. Anderson Masonry was the subcontractor that handled the rock work that was used for retaining walls, guard walls and decorative arches along the road.

Much of the masonry work involved “disguising” modern reinforcement materials, Baron said.

Masonry “re-pointing” involved taking out bad mortar and replacing it on existing retaining walls.

The project has involved the installation of extensive rock and concrete guard walls and three different types of removable guardrails, the most recent being log guardrails.

Stabilizing slopes above and below the road was another major facet of the project. That involved more than a mile of reinforcing bolts.

A material called shotcrete was used in some areas by a subcontractor that has also done rock work in zoos, Baron said.

“They do an excellent job of disguising their work,” he added.

Visitor use improvements, such as the construction of walkways, additional parking and “crow’s nest” viewing areas, were carried out in multiple locations.

One improvement came about by chance after the park was pounded by 1 1/2 inches of rain in 30 minutes last June. The torrent caused a series of debris slides on the road.

One slide dumped 500 cubic yards of material across the road at Big Bend. That material was used to significantly widen the visitor-use area next to the road. “We took advantage of it,” Baron said.

Gordon unveiled a schematic for significant improvements at the Sun Point visitor use area, one of the last big pieces of the project.

“We’re looking forward to doing this,” he said.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.