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March/April 2004
A Tale of Two Canyons
by Steve MolerColorado DOT applies lessons learned from the Glenwood project to a similar highway in the Snowmass valley, near the famed Aspen ski resort.
The Colorado Department of Transportation (CDOT) knows a thing or two about building highways through complex terrain. In 1992, CDOT completed an award-winning project that extended I–70 through Glenwood Canyon, finishing the last section of an interstate that stretches from Baltimore, MD, to Cove Fort, UT. The project later received the 1993 Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers and is considered one of the greatest highway engineering accomplishments in U.S. transportation history. (See "Glenwood Canyon 12 Years Later".)
Not one to rest on its laurels, shortly after finishing Glenwood Canyon the CDOT began planning a project in Snowmass Canyon 56 kilometers (35 miles) away. The Glenwood and Snowmass projects are remarkably similar. Both involve upgrading overburdened two-lane highways to four lanes through extremely narrow, ecologically sensitive canyons to improve safety and mobility while minimizing environmental impacts. "Both required exceptional planning, the latest in context-sensitive design, and construction ingenuity," says Ralph Trapani, the CDOT project manager on the Glenwood Canyon project, now a private consultant.
The project in Snowmass Canyon, which began in September 2000, applies the lessons that CDOT learned in Glenwood to upgrade a section of highway northwest of the ski resort town of Aspen. The $100 million project consists of widening 5.6 kilometers (3.5 miles) of State Highway (S.H.) 82 through Snowmass Canyon, a narrow valley carved by the Roaring Fork River. Like Glenwood Canyon, the Snowmass Canyon project involves building two roadwaysone virtually on top of the otheralong steep, geologically unstable slopes using a terraced system of retaining walls and bridges to minimize environmental impacts.
(Above) While the up-valley lanes took shape in Snowmass Canyon during the summer of 2003, the old two-lane highway to the right carried traffic one way up the valley. The two-lane county road across the river to the right carried westbound traffic down the valley. Photo: Joseph J. Kracum, Kracum Resources, LLC.
Cross-Sectional View of the Snowmass Canyon Project
A. After workers install fences (yellow poles) to preserve the environment, construction begins with vertical cuts into the hillside (upper right) for the up-valley lanes. Soil-nail walls using corrosion-proof steel bars are installed to stabilize the slope. Then the construction crew members install reinforced steel and anchor plates and spray shotcrete onto the vertical surface to complete the reinforced system.
B. The process is repeated as the crew installs a second set of retaining walls into the hillside. Mass excavation is necessary to reach the bottom of the footing elevation for the walls that support the roadway.
C. Shafts are drilled vertically into the bedrock and filled with reinforced concrete. The workers then construct a reinforced concrete footing at the top of the shaft and drill through the footing to the bedrock to place the tieback ground anchor. This system of compression and tension handles the extreme forces that act on the earth retaining system.
D. An architecturally finished precast panel is placed vertically on the footing. Reinforcing, structural backfill and embankment then are placed on top. Pavement, traffic signs, concrete barriers, guardrails, and striping complete the up-valley lanes.
E. Construction on the down-valley lanes begins with excavation for the retaining wall foundations (lower left). The crew places the precast wall panel vertically on the footing, and reinforcement grids are attached to the panel. Structural backfill material placed and compacted in lifts helps form the mechanically stabilized earth wall, and embankment material is placed next. Finally, pavement, traffic signs, concrete barriers, guardrails, and striping are added to complete the down-valley lanes.
To view an animated slideshow of this cross-sectional sequence, visit www.sh82.com/snowmasscanyon.html.
This drawing illustrates how the terraced system enables CDOT to construct a four-lane divided highway through the narrow canyon.
Saving the Hardest for Last
Snowmass Canyon represents the final section of roadway in a three-decade-long project to upgrade S.H. 82 from two to four lanes between Glenwood Springs and the Aspen area. As with Glenwood Canyon, which was the final segment of I–70 to be completed, the Snowmass Canyon section of the S.H. 82 upgrade was saved for last because it encompassed the route's most difficult environmental, engineering, and financial challenges.
On October 14, 1992, the day CDOT cut the ribbon opening the Glenwood Canyon project, many of the project's planners, designers, and engineers turned their full attention to the difficult section of S.H. 82 between Basalt and Aspen, which contains the Snowmass Canyon segment. This 27-kilometer (17-mile) stretch of highway through some of the most scenic and majestic countryside in the United States had become one of Colorado's most dangerous two-lane highways for many of the same reasons that Glenwood Canyon attained a similar status a decade earlier. Undercapacity, high traffic volumes, sharp curves, narrow lanes and shoulder widths, lack of acceleration and deceleration lanes, and inadequate sight distances for passing eventually earned S.H. 82 the grim nickname "Killer 82."
By late 1992, CDOT had published a draft environmental impact statement for the section starting just east of Basalt and ending near Aspen. But CDOT and the Federal Highway Administration (FHWA) ultimately published a final environmental impact statement in October 1993 that covered the section from just east of Basalt to the Buttermilk ski area just outside Aspen. Upgrading the section inside the town of Aspen was considered in a subsequent environmental impact statement for the entrance to Aspen.
Before (top) and after (bottom) renderings illustrate how CDOT is constructing a four-lane divided highway through the narrowest possible footprint to minimize environmental impacts. Photos: CDOT.
Finding a Preferred Alternative
The primary debate over roadway alignments focused on whether to construct a one-way couplet for down-valley westbound traffic on the side of Roaring Fork River opposite the existing S.H. 82 through Snowmass Canyon. The new alignment would roughly parallel an existing railroad right-of-way. The up-valley eastbound traffic would use the old S.H. 82 roadway. Although this alternative would have saved millions in project costs, CDOT eventually rejected it because of the adverse impacts on wildlife and property owners along the proposed right-of-way.
As the preferred alternative, CDOT and FHWA selected an alignment slightly higher up the canyon slopes from the existing highway, because it would have the least environmental and social impacts. The chosen alternative forced planners and designers to face the same predicament they had experienced with Glenwood Canyon: how to cram four lanes of roadway into an extremely narrow footprint, bordered by a river on one side and steep canyon slopes on another, without harming the environment.
"The solution was challenging," says Joe Elsen, CDOT's manager for the Snowmass Canyon project. "We were fortunate to be able to apply our knowledge and experience from Glenwood to the Snowmass Canyon site."
During the drafting of the environmental impact statement, local county officials and the public wanted to evaluate transit options in addition to the four-lane highway. Five intermodal alternatives were developed, including a no-build option that served primarily as a baseline for evaluating the other alternatives. The preferred alternative provides for bus and high-occupancy vehicle lanes in some sections, bus park-and-ride facilities, a multimodal transfer station at the Buttermilk ski area, and a future commuter rail corridor that currently is under study.
Snowmass Video Facilitates Technology Transfer
"The construction of I–70 through Glenwood Canyon, CO, is a marvel of innovation in highway design and construction," says Ron Speral, a program delivery engineer in FHWA's Colorado Division who served as an operations engineer during the Glenwood project. A series of videos highlighting the project's numerous planning, design, environmental, and construction innovations brought these achievements home to many in the profession of civil engineering.
Joe Elsen, the CDOT manager for the Snowmass Canyon project, previously worked as an engineer on Glenwood Canyon. Elsen's experience with the videos of the Glenwood project provided the impetus to film the construction in Snowmass Canyon. The video enables the Snowmass team to share with a wider audience the technological innovations used to reconstruct the section of S.H. 82 near Aspen.
"Being involved with the videos," Elsen says, "and knowing how often requests came in for them made me realize just how effective this medium is for transferring technology."
Elsen describes video as the ideal medium for encapsulating the technology because it not only appeals to a broad audience of decisionmakers who need the information, but it also helps viewers visualize the technologies and their applications. Elsen imagines an engineer watching the video and thinking: "There's our solution. Why reinvent the wheel?"
The 25-minute video focuses on how CDOT and its consultants and contractors are using innovative construction techniques to overcome the challenges of building a four-lane divided highway through a narrow, environmentally sensitive corridor. Among the techniques featured are mechanically stabilized earth walls that combine precast panels with geogrids and recycled structural backfill that combines alluvial and colluvial soils to avoid waste. Other technologies include precast, post-tensioned double-T walls, tieback and soil-nail walls, micropiles for shoring precast L-walls, and geotechnical instrumentation that ties all the systems together.
Viewers will see how the geotechnical designer employed innovative analysis techniques, how the contractors planned their operations given limited access, and how they handled value-engineering change proposals, an administrative process that allows a contractor to bring innovative ideas and solutions to the project beyond what was originally contracted.
Produced by a company in Glenwood Springs, CO, the video is offered in both VHS and DVD formats and serves as a learning tool and historical record of the project's achievements.
For more information about the Snowmass Canyon project or video, contact Joe Elsen at joseph.elsen@dot.state.co.us.
A precast concrete panel with attached geogrid forms one of the project's mechanically stabilized earth walls.
Geotechnical Complexities
Although Glenwood Canyon is almost four times longer, Snowmass Canyon arguably is more complicated, at least from a geotechnical standpoint. After more than 2 years of geotechnical studies and analysis, CDOT decided to construct more elaborate and complex soil-nail, tieback, and double-T walls using various types of post-tensioned ground anchors embedded in the bedrock to stabilize the hillsides. The department is building these earth retaining systemssome as long as 1,200 meters (4,000 feet)on both the up-valley and down-valley lanes. In all, the project includes 6 bridges and some 42 earth retaining systems.
"Anything that's considered state-of-the art from a geotechnical standpoint we're doing on this project," says CDOT project engineer Pete Mertes. "We have a great team of experts making this project a success."
A precast architectural panel covers a soil-nail wall.
A double-T retaining wall takes shape in September 2002 at the approach to Bridge No. 2, one of the project's two 290-meter (950-foot) bridges.
Environmental Protection
The project's strategies to protect the environment rival and in some cases exceedthose employed in Glenwood Canyon. "CDOT has gone to great lengths to align the new highway based on established deer and elk migration routes," says Elsen.
Two of the project's six bridges are designed strictly as game crossings, allowing deer and elk to pass underneath the highway at ground level. An elaborate management system for storm water and a plan for controlling erosion are among the many measures CDOT is employing to help maintain the integrity and health of the Roaring Fork River and preserve its riparian zones.
"In Glenwood Canyon, the reconstruction required that we fix the banks of the Colorado River that were denuded or constructed hastily using rip-and-tear techniques," Elsen says. "But with Snowmass, we were able to avoid touching the Roaring Fork River."
Tree preservation is a major component of environmental preservation, as it was in Glenwood Canyon. CDOT designed much of the up-valley alignment to avoid as many stands of larger, more mature trees as possible. The space between the up-valley and down-valley lanes stands as an environmental island of untouched trees and vegetation. Disturbed areas will be replanted with native vegetation to return the canyon to its original condition.
With respect to recreation, CDOT took a page out of Glenwood Canyon's playbook, providing bicyclists with 2.5-meter (8-foot)-wide shoulders along the roadway for safe cycling. CDOT also created pedestrian access to the river at various points.
In August 2003, the up-valley lanes were near completion. Since this photo was taken, traffic has been diverted to the now-completed up-valley lanes.
Traffic Mitigation
One advantage at Snowmass Canyon that CDOT did not enjoy in Glenwood was access to an alternate route to detour traffic during construction. In Glenwood, traffic had to be stopped for 30 minutes on average to allow construction crews to work because there was simply nowhere to divert traffic.
In Snowmass Canyon, during construction of the up-valley lanes (those at higher elevations), CDOT could divert one lane of traffic from S.H. 82 onto a county road located on the other side of the Roaring Fork River. Traffic going in the opposite direction could use one lane of
S.H. 82. This arrangement not only reduced the number and length of traffic delays but also gave construction crews more room and flexibility to work.With the up-valley lanes now complete and handling all two-way traffic, the detour is no longer necessary. Construction of the down-valley lanes is in full swing. When CDOT completes the project as early as fall 2004, 1 year ahead of the original contract completion date, perhaps the improvements in Snowmass Canyon will lead motorists to consider changing the highway's nickname from "Killer 82" to "Son of Glenwood Canyon."
Bridge No. 2 is shown under construction in September 2002. Traffic passes by the new bridge traveling on the old S.H. 82 on the right.
Steve Moler is the public affairs specialist at FHWA's Resource Center office in San Francisco.
Susanna Hughes Reck, the technology deployment specialist at FHWA's Lakewood, CO, satellite office of the Resource Center office in San Francisco, assisted with the sidebar on the video project for Snowmass Canyon.
For more information about the project in Snowmass Canyon, visit www.sh82.com/snowmasscanyon.html.itates Technology Transfer
Other Articles in this issue:
Coordinating Incident Response
Erosion Control with Recycled Materials
Glenwood Canyon 12 Years Later
A Tale of Two Canyons
The AIRS Approach to Analyzing Intersection Crashes
March/April 2004 · Vol. 67 · No. 5
