In San Juan and Ouray counties in Colorado, the Colorado Department of Transportation is working on a project to repair five existing crib walls on Red Mountain Pass (U.S. 550). The purpose is to improve the safety and integrity of the roadway by reinforcing the under-highway embankment support walls.
The work will include the construction of a reinforced concrete slab underneath the roadway (at Ruby Walls), and rock excavation at MP 79.
The average daily traffic on this stretch of U.S. 550 is reportedly 2,164.
Work progressed from July 7 to Nov. 15, when the winter shutdown began. Weather permitting, it will resume again in mid-April and continue through late June 2016.
The project has a $5.7 million total estimated budget, which will not be finalized until the project’s completion. Funding is a combination of retaining wall construction funding, Federal Emergency Relief (Ruby Walls), and Public Lands Highway funds.
The prime contractor is Rock & Company, Brighton, Colo., under the direction of vice president Scott Davis.
According to Ed Archuleta, P.E., CDOT Region 5 program engineer, the challenges with the project are too numerous to list, but a few include the narrow roadway, high elevation that is prone to snowfall (which did come in early November, resulting in this season’s wrap up of work a couple of weeks early), and finally “rock, rock, and rock.”
Davis added that major challenges with the site include “very steep slopes, falling rock, and the very narrow work site. Maintaining safe and timely traffic flow also is a major challenge, as much of the work is within, above, or beneath the travel lanes.”
Archuleta explained that Red Mountain Pass is designated as a Scenic Byway, which is a prime tourist corridor for the local communities.
“The roadway has historical significance which is dealt with in the design, and few bidders are interested in working in this location,” he said. “There is a short construction season with risk of weather from snow in spring and fall as well as rain monsoons in the summer.”
One particularly unique feature of the project is its geotechnical engineering challenge.
“These walls were built more than 50 years ago with no ’as-builts’ and/or design to refer to in order to determine what we will uncover, hence there are design modifications during construction,” Archuleta said. “Everyone walks away with a sense of accomplishment after completing this kind of challenging project on this historic highway.”
The project consists of three work sites (1, 2, and 3). Work sites 2 and 3 are located north of the summit. Work site 2 is just south of Engineer Pass turn-off and work site 3 is just north of the turn.
According to Davis, work site 2 (MP 88.5) included three major Mechanically Stabilized Earth (MSE) retaining structures holding up the southbound lane, totaling 2,561 sq. ft. (238 sq m). One of the walls contains a new 36 in. (91.44 cm) diameter steel culvert (replacing an old failed culvert). In order to complete this wall, a soil nail retaining wall was installed (to support a single lane of traffic while building the MSE retaining wall). A total of 58 soil nails and 144 sq. yds. (120.4 sq m) of shotcrete were used in constructing the soil nail wall. Approximately 1,200 cu. yds. (917.47 cu m) of rock and soils were excavated and replaced with specified structural backfill.
Davis reported that work site 3 (MP 89.5) saw the completion of a concrete moment slab stretching nearly 700 ft. (213.3 cm) long under the southbound lane. Approximately 245 cu. yds. (187.32 cu m) of structural concrete and 33,750 lbs. (15,209 kg) of reinforcing steel were placed in the moment slab. A total of 1,272 linear feet (387.70 lm) of rock anchors were installed to anchor the slab to the bedrock. Both lanes, for approximately 700 linear feet (213.36 lm), received a pavement overlay and striping over the new moment slab.
Finally, Davis noted that work site 1 (MP 79) saw the drilling, blasting, and hauling off of approximately 7,000 cu. yds. (5,351.88 cu m) of rock from above the roadway on the southbound lane. This excavation will facilitate moving the roadway further away from the steep downward slopes, and provide more room for stabilization structures (similar to those used at site 2 — MSE and soil nails — to be completed next season).
Major subcontractors listed by Davis include Alert Traffic Control for traffic control, Franklin Drilling and Blasting for rock blasting, Rocky Mountain Aggregates and Construction for hauling and material processing, and United Contractors for paving and concrete supply.
Major equipment used includes a John Deere 664 D loader, a John Deere 304 J loader, a Komatsu PC 228 excavator, a Komatsu PC 78 excavator, a Sakai 48 in. (122 cm) roller compactor, a GMC Side Kick single axle dump truck, and an Ingersoll Rand ECM 360 rock drill.
“Additional work was completed at site 3 by others, including repair of damaged power lines and scheduled rock fall mitigation maintenance,” Davis said. “Working in cooperation with the other contractors, Rock & Company completed its established contract goals and returned the roadway to the public ahead of schedule.”
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