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Publication Number:  FHWA-HRT-14-006    Date:  September/October 2014
Publication Number: FHWA-HRT-14-006
Issue No: Vol. 78 No. 2
Date: September/October 2014

 

A Crowning Achievement

by Marili Green Reilly

The Oregon DOT and its partners used innovative solutions to protect and restore a historic viaduct.

Crown Point and Vista House, shown here, are a major tourist attraction along the Historic Columbia River Highway. The pedestrian viaduct that nearly encircles Crown Point recently underwent a major restoration.
Crown Point and Vista House, shown here, are a major tourist attraction along the Historic Columbia River Highway. The pedestrian viaduct that nearly encircles Crown Point recently underwent a major restoration.

What do you do when you have a 100-year-old pedestrian viaduct perched high on an iconic promontory that draws 1 million visitors a year, but the structure is in danger of catastrophic failure if a vehicle so much as jumps the curb? You get creative about making repairs.

That is what engineers with the Oregon Department of Transportation (ODOT) did as they pondered their options for renovating a deteriorating pedestrian structure located along the Historic Columbia River Highway. The highway, which connects Portland to eastern Oregon, is one of only two roads in the United States designated as a National Historic Landmark, an All-American Road, one of America’s Byways®, and a National Historic District, among other distinctions.

The pedestrian viaduct parallels the roadway all the way around scenic Crown Point, a National Natural Landmark, and the Vista House, a 1916 structure housing a museum and gift shop. The viaduct is a separate structure that was built before the roadway. Although they are structurally independent, the pedestrian viaduct and the roadway look like one seamless structure from the top, with the road next to the sidewalk separated by a curb. The sidewalk is what is supported by the viaduct, as the road is at ground level.

The pedestrian viaduct had seriously deteriorated and was in imminent danger of failure. Foregoing rehabilitation would have eventually forced ODOT to close the sidewalk to pedestrian use. ODOT officials also were concerned about what might happen if a bus or other heavy vehicle should unintentionally jump the curb onto the sidewalk. Such an event might have caused the viaduct to collapse, necessitating the closure of that portion of the highway and resulting in a serious hit to the local and regional economies.

The solution? ODOT joined forces with the Federal Highway Administration’s (FHWA) Western Federal Lands Highway Division and the Oregon Parks and Recreation Department to restore the Crown Point Pedestrian Viaduct safely, efficiently, and without damaging the existing viaduct or the historic highway.

A Little History

Built between 1913 and 1922, the Columbia River Highway was the first modern highway constructed in the Pacific Northwest. Samuel C. Lancaster designed the road to take full advantage of every natural aspect, scenic feature, waterfall, viewpoint, and panorama as it passes through the Columbia River Gorge. It was the Nation’s first scenic highway.

Located on the south bank of the Columbia River, the portion of the highway now designated in three counties as a National Historic District begins 14 miles (23 kilometers) east of Portland in Troutdale, OR, and stretches about 74 miles (119 kilometers) to The Dalles, OR. Although portions of the original highway have been converted into scenic trails and much of it has been demolished and replaced by I–84, the 22-mile (35-kilometer) stretch of roadway from Troutdale to Dodson, OR, continues to draw visitors to its many scenic overlooks, parks, and waterfalls.

At the western gateway to the gorge, Crown Point rises 733 feet (223 meters) above the Columbia River and provides visitors with a panoramic view. Vista House was built on this point between 1916 and 1918 as a scenic wayside for travelers and, under the stewardship of the Oregon Parks and Recreation Department, still operates as a visitor center today. The deteriorated pedestrian viaduct adjacent to the section of the Historic Columbia River Highway that partially encircles that iconic promontory threatened the safety of visitors to the popular landmark.

Specific Problems

The Crown Point Pedestrian Viaduct is a nearly 600-foot (183-meter)-long concrete structure that carries a 7-foot (2-meter)-wide sidewalk and flanks the roadway, which loops approximately 270 degrees around the rocky point. The viaduct is supported on the outside by 30 columns and another 29 columns buried in the masonry wall that supports its interior edge. The top of the masonry wall is also where the viaduct meets the roadway.

Among the major issues ODOT faced with the viaduct was that it was pulling away from the roadway, despite being temporarily supported by timber reinforcements. The concrete underside of the viaduct’s deck also had disintegrated so much that the rebar was exposed in many places. In addition, a bulge had appeared in the rock masonry wall, indicating movement or stresses beneath the roadway, and an extensive network of cracks marred the sidewalk and the parapet railing at the edge of the deck.

While considering the necessary repairs, the project team also had to factor in the requirements of Section 106 of the National Historic Preservation Act and Section 4(f) of the U.S. Department of Transportation Act, because the viaduct is part of the historic highway.

Partners Choose Innovations

With so many constraints to work around, the design team had to think outside the box. FHWA and ODOT worked closely with Oregon’s State Historic Preservation Office to identify design solutions that would minimize visual impacts on the historic structure.

The sidewalk sits atop the pedestrian viaduct, which parallels the roadway around Crown Point. Although they look like one structure to visitors on the deck, the roadway and the sidewalk are supported separately.
The sidewalk sits atop the pedestrian viaduct, which parallels the roadway around Crown Point. Although they look like one structure to visitors on the deck, the roadway and the sidewalk are supported separately.

Ultimately, the solution involved constructing an entirely new structure underneath the historic viaduct, but otherwise maintaining the function and look of the original sidewalk. The new support structure is strong enough to hold not only its own weight but also that of the aging viaduct. Most important, the new support structure is hidden from public view, retaining the historic look for visitors.

To accomplish the restoration, the construction team used several unconventional methods, including the installation of micropiles, the use of self-consolidating concrete, and the injection of epoxy sealant into cracks. Here is a closer look at these methods and how they each contributed to strengthening the old viaduct’s structural elements to provide an additional 50 years of service life.

Micropile Installation

One of the largest unknown factors on the project was the condition of the viaduct’s existing substructure. In fact, the project team had no idea about the condition of the footings. They referred to as-built plans that were adjusted after the original project’s completion 100 years ago. However, once they started the project, they did not find what the documents depicted.

“The footings were a lot thinner than we expected,” explains Margaret Moen, project engineer with FHWA’s Western Federal Lands Highway Division. “We were surprised that they lasted as long as they did.”

These columns supporting the outer edge of the pedestrian viaduct were badly deteriorated.
These columns supporting the outer edge of the pedestrian viaduct were badly deteriorated.

The team did know that the bulge that had appeared in the stone masonry beneath the viaduct suggested something was pushing the rock out. And they knew that conventional pilings were out of the question to add support beneath the viaduct because of the vibrations and heavy equipment associated with their installation.

“No one knew how much vibration the structure could take,” says Matthew Fletcher, FHWA’s assistant project engineer. “If too much vibration was applied to the soil, the viaduct could crumble. If the viaduct failed, the road would fail too, and you’d have a really difficult time ever building anything back there again.”

Micropiles provided the answer. Installation of micropiles requires smaller, lighter, less intrusive equipment, and causes much less vibration than conventional pile drivers. FHWA’s Moen describes a micropile as “a 1.5-inch [3.8-centimeter] steel bar inside a 7-inch [17.8-centimeter] casing, which is filled with grout.”

For this project, the construction team installed micropiles a mere 10 inches (25 centimeters) from the existing columns. During the work, the installation equipment was staged on the roadway to avoid putting any load on the existing pedestrian viaduct.

For the interior columns, which are hidden within the rock masonry wall, the design called for a single, vertical micropile to be drilled through the existing footing of each of the 29 interior columns.

The construction crew inserted the casing during drilling, then the drill bit folded in and was pulled out. The crew then inserted the micropile and filled it all with grout. Once installed, the micropile received a cap to seal it. After installation of all the micropiles, the construction crew paved the area to cover the caps of the micropiles and complete the surface.

Due to the variation between the historic plans and what they found in actuality, team members were uncertain whether they hit all the interior column footings. But as Moen points out, “with the micropiles and the way the new support structure was connected into the existing viaduct, it didn’t matter whether we hit them or not. We replaced what was there.”

To complete the foundation of the new structure, the construction team placed 11 micropiles adjacent to selected exterior columns. Not all the exterior columns were deteriorated enough to warrant a micropile, but they did all receive additional reinforcing steel and a new concrete shell. In total, they installed 40 micropiles.

According to the project designer, Amanda Blankenship, a bridge engineer with David Evans and Associates, Inc., “The existing columns were about 12 inches [30 centimeters] square and some of the external columns were as much as 18 feet [5 meters] tall, so they needed to be strengthened.”

Each of the external columns was further strengthened with an additional 5 inches (13 centimeters) of concrete on three faces. All of the columns received the new concrete sheath, making them almost 2 feet (0.6 meter) square.

“The original front face of the column is still exposed,” says Blankenship, which helped to retain the visual integrity of the structure. Although the columns are not in public view from atop the point, they are visible in many aerial views of Crown Point. “We didn’t want to draw attention to the new concrete, so it is tinted one shade darker than the existing concrete. We tried to preserve the slender look of the columns. If you walk down there, you will see the new concrete, but you can still see the slender shapes of those columns.”

Because the micropile installation equipment took up so little room, the construction team rarely needed to close more than one traffic lane. “That highway is a wonderful engineering marvel that attracts a lot of tourists and visitors,” says Larry Olson, a district manager in ODOT’s Region 1, who leads maintenance operations on the Historic Columbia River Highway. “So the contractor was challenged to keep it open while still doing the work. A lot was done with single-lane flagging operations, but there were also times when parts of the road were closed for months at a time during the winter. That gave them an opportunity to be more productive without having to address the needs of traffic.”

Micropile technology is not new. In fact, the Western Federal Lands Highway Division has used micropiles on other projects, and the design team that worked on this project also has incorporated micropiles at other sites with difficult access, such as a small pedestrian bridge. But for this project, the technology was the ticket to safeguarding the historic structure and preserving its visual integrity.

Soil Nails and Shotcrete

In addition to the micropiles, the retaining wall beneath the viaduct was reinforced with soil nails. The 100-year-old rock masonry wall ranges in height from less than 4 feet (1.2 meters) at each end to about 18 feet (5.5 meters) near the center and is recessed behind the exterior columns the entire length of the viaduct.

To reinforce the hillside behind the wall, the construction team worked from top to bottom, removing the stones from one 4-foot (1.2-meter) square section at a time, constructing a structural shell with shotcrete, and then installing soil nails. Once the initial concrete shell was completed, the team members prepared the wall for a final application of shotcrete by rappelling themselves down the face of the wall.

Finally, to return the wall to its original appearance, the construction crew replaced the rocks. The team set up scaffolding in front of the wall and reset all the stones one by one.

“It turned out to be a really nice rock wall,” ODOT’s Olson says. “It’s really a shame that it’s something that people never see.”

Construction team members reinforced the existing columns with micropiles inserted adjacent to the columns, then cast a concrete sheath (shown here) around three sides. The concrete is a darker gray to recede into the shadows.
Construction team members reinforced the existing columns with micropiles inserted adjacent to the columns, then cast a concrete sheath (shown here) around three sides. The concrete is a darker gray to recede into the shadows.

Self-Consolidating Concrete

This project would not have been constructible without the use of self-consolidating concrete. This advanced product is considered a new technology and is fluid when cast. The fluidity enables it to flow and to fill the shapes of the form more easily than traditional concrete. This made it easy to place concrete underneath the existing viaduct’s deck where typical concreting methods would not suffice.

At the outset, Kristen Stallman, the historic highway’s coordinator in ODOT Region 1, says, “If you went underneath the viaduct, it was particularly scary to see how all the beams and piers were crumbling and falling apart.”

Crew members prepare the wall for a final application of shotcrete.
Crew members prepare the wall for a final application of shotcrete.

Blankenship adds, “From the top you could tell that the sidewalk had been patched, but from below you could see the exposed reinforcing that was heavily corroded.”

Despite the extensive deterioration, the project team could not directly replace the sidewalk because it would have changed the visual appearance of the historic structure. Instead, they had to build the supporting viaduct underneath the original, which meant the team did not have traditional access to pour concrete into open forms. The limited access allowed only for pumping the concrete through small portals on the exterior vertical face.

Self-consolidating concrete was ideal for this application also because it requires no external vibration during placement. “The self-consolidating concrete works in areas highly congested with rebar,” says FHWA’s Fletcher. “Any normal concrete would have a hard time getting in there; you need it to flow to those locations to surround all of the heavier reinforcing steel. It’s essentially the same as any normal concrete except they remove the coarser aggregate and substitute smaller, finer aggregate, while also adding extra admixtures to help suspend the sand. You can imagine that sand will flow a little more easily than rock does in congested rebar areas.”

The top of finished micropiles are visible here next to the wall.
The top of finished micropiles are visible here next to the wall.

Epoxy Crack Sealing

Although the vast majority of the viaduct work happened below the structure, some work did occur on the deck. Most notably, the existing viaduct had more than 2,000 feet (609 meters) of visible surface cracks that the project team had to seal to eliminate further water infiltration and crack growth. The solution involved a noninvasive process in which epoxy is pressure injected through tubes into the cracks.

The process is simple, Fletcher explains. “When they see material spewing out of an adjacent port, it tells them that all the voids in between are filled. Then they put a cap on it and move to the next one,” he says.

Although there is less visual impact from this application than from other alternatives, FHWA’s Moen was concerned about the repairs being noticeable so she called in ODOT’s inspectors. According to Moen, “They said, ‘It’s a repair job, we expect to see it, and over time the repair will weather and not be so noticeable.’”

Keeping the Public Informed

Because of the large number of visitors at Vista House each year, it was imperative to keep the attraction open. Kevin Price, the Portland and gorge district manager with the Oregon Parks and Recreation Department, says, “My friends all say, ‘When I have people come in from out of town, that’s where we take them. You get to see the view from Vista House and then travel on to all the waterfalls within a 10-mile [16-kilometer] stretch.’” Price also brings children who live in Portland to Crown Point and Vista House to make them aware of the opportunities available to them in State parks.

Despite the nature of the replacement work, the historic highway needed to remain open during much of the construction. During the times when road closure was necessary, however, ODOT needed to keep the public informed.

Mike Odom, project manager with FHWA’s Western Federal Lands Highway Division, made sure that various stakeholder and interest groups knew about scheduled closures. “We worked really hard to coordinate with bike groups, tour groups, schools, and public services to find the best times when we could close these roads and have the least impact,” he says.

Odom worked hand in hand with ODOT’s public relations staff, who took the lead to spread the word about closures. ODOT reached out to the media through press releases with updates about the design and construction of the project. Staff members also participated in a number of interviews for television news segments. “I think the partnership with ODOT and the public involvement effort really made a difference in the success of minimizing impacts on people wanting to come out and see Crown Point,” says Odom.

ODOT’s Stallman published dates and times of road closures, as well as links to the project Web site (www.wfl.fhwa.dot.gov/projects/or/crown point), in ODOT’s online newsletter. Friends of the Vista House, the group that operates the visitor center, played an essential role in keeping Vista House open during the construction. The group had to get the message out to the public that “yes, you can come up to the gorge. Even though the road is closed where it loops around Crown Point, you can still get as far as Vista House and the parking lot,” explains Stallman.

Photo. Two high-pressure hoses are shown inserted into the underside of the existing viaduct.
Workers used high-pressure hoses to inject epoxy grout into cracks on the underside of the existing viaduct to seal them. They used the same process on the deck (not shown).

 

The finished viaduct, shown here from the east side, is structurally sound but retains the historic look of the original.
The finished viaduct, shown here from the east side, is structurally sound but retains the historic look of the original.

Keeping the site open to the public also meant welcoming special visitors, like car manufacturers, who often film commercials on the old highway. One company released a TV commercial right at the start of the project in which the advertised car was shown driving around Crown Point. Another filmed a commercial during the project. “The contractor worked with them to allow it to happen,” says FHWA’s Fletcher. “The filming didn’t affect the project at all.”

A Win-Win-Win Project

By the end of the 2013 construction season, most of the repairs were complete. The periodic road closures were helpful to both ODOT and the Oregon Parks and Recreation Department. In fact, ODOT maintenance crews were able to do some heavy maintenance that they are unable to do when the road is open. For example, crews removed some trees, cleaned the moss off the old walls, and did some other repairs. The parks department did some vegetation management, opening up views that had grown closed.

With the project now complete, ODOT can rest easier knowing that the viaduct is once again safe. The potential for damage should a vehicle jump the curb and end up on the sidewalk/viaduct is no longer a concern — even for the largest tourist buses that come to Crown Point.

In addition to securing the structure and enabling long-overdue maintenance activities to occur, the project was also a “win” from a partnership perspective. Funding had been an issue for ODOT in the beginning, but partnering with FHWA’s Western Federal Lands Highway Division helped the department secure the funds to get the job done.

Olson recognizes the value of ODOT’s partnership with FHWA. “I appreciate the professional working relationship we have with an agency that fully addresses the needs of a project,” says Olson. In fact, ODOT currently is working with the Western Federal Lands Highway Division to design and deliver several more projects along the Historic Columbia River Highway in the coming years.

Price, with the Oregon Parks and Recreation Department, expressed a similar reaction. “Over the years, we’ve worked very closely with other agencies — ODOT, FHWA, the U.S. Forest Service, different counties — and those partnerships that make all of this possible astound me,” he says. “It does nothing but benefit the public.”

To Price, the true payoff is for visitors. “The Historic Columbia River Highway is a lifeline that allows visitors to travel from viewpoints like Portland Women’s Forum, Crown Point, and Vista House on to Latourell Falls, Shepperd’s Dell, Bridal Veil Falls, Wakeena Falls, Multnomah Falls, and Horsetail Falls,” he says. “Certainly the construction was an inconvenience, but in my mind that small inconvenience will pay dividends for many years to come as it benefits the millions and millions of visitors who come to see what we refer to as the ‘Jewels of the Gorge.’”


Marili Green Reilly is the historian for FHWA’s Western Federal Lands Highway Division. She has compiled a series of remembrances on the history of Western Federal Lands from retired project engineers. The series is titled “A Glimpse into an Earlier Era” and is available on the division’s Web site at www.wfl.fhwa.dot.gov/about/history/articles.htm. Reilly joined FHWA more than 30 years ago and holds a bachelor’s degree in liberal arts from Portland State University.

For more information, contact Marili Green Reilly at marili.reilly@dot.gov or 360–619–7802.

The author would like to thank Matthew Fletcher, Samantha Gould, and Margaret Moen for providing technical assistance for this article.

 

 

 

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