Challenging Bridge Construction In Cloudland Canyon

By Steve Hudson | September 28, 2010

Bridge construction always brings challenges — and it's not always the biggest bridges that offer the biggest challenges. A good case in point is the recently completed bridge over Daniels Creek in Cloudland Canyon State Park in northwestern Georgia, a project that involved everything from unbelievably rugged terrain to the necessity of placing beams by helicopter.

The bridge, a key part of the park's trail system, crosses a major creek and connects with existing trails to enhance the experience of park visitors who explore the site. The original concept was for construction of a cable suspension bridge, but that proved much too expensive and prompted the team to look at alternatives.

What ultimately emerged was a design using glue-laminated wood beams and metal grate decking, designed by David G. Smith & Associates,Gainesville, Ga. MACTEC Engineering & Consulting handled the geotechnical aspects of the design. Contractor K.W. Raines Associates, based in Henagar, Ala., was chosen to build it. Buddy Harrison, Georgia State Parks northern region engineering and construction manager, served as project engineer.

The bridge, with a total length of close to 90 feet and a width of 6 feet, crosses the creek in two spans. One has a length of 46 feet 4 inches feet. The other is 39 feet 6 inches long.

Plans called for a total of 10 glue-lam beams to be used in the bridge — five beams in each span. Each beam is constructed of multiple thinner pieces of wood that have been laminated together using glue and pressure. The beams used in this bridge measure 5.125 inches wide and 23.375 inches deep and have a maximum length of about 47 feet.

Anchoring A Boulder

The spans connect with one another and make a bend of about 45 degrees at an intermediate bent that's built atop a large boulder sitting in the middle of the creek — and so one of the first steps in construction was to securely anchor the boulder to bedrock.

"Our trails crew used a rock drill and Dywidag rock anchors to secure the boulder using five anchor rods," Buddy Harrison says. The drill and anchor rods were brought in along existing trails using a Kawasaki Mule, then manually transported to the boulder itself.

Working atop the boulder, the DNR trails crew quickly installed the five rock anchors needed to secure the rock. Before drilling, it was necessary to sandbag and grout some areas at the boulder's base to allow the anchors to be installed. These anchors had a total length of about 25 feet each, plenty to securely anchor the boulder to bedrock, and Harrison explains that this part of the work was completed quickly and smoothly.

Concrete Work

Once the boulder was securely anchored, attention turned to construction of the end abutments and the intermediate bent. Rock anchors were also called for at the end abutments — three at one abutment location, and two at the other.

Once the anchors were installed, contractor K.W. Raines' concrete crew first constructed the necessary formwork and installed the specified reinforcing steel. The crew then poured each structure utilizing flyash concrete, mixed on site and pumped to each placement location.

"The design called for a 3,000-psi mix," Harrison notes, "but the mix we used was breaking at closer to 8,000 psi."

All concrete components, including flyash, sand and cement, were transported to the mixing site using skid steers and rough terrain forklifts.

Beams By Helicopter

With the concrete work completed, the team turned its attention to delivery and placement of the glue-lam timber beams.

Originally, the plan had been to deliver the beams to the job site by hauling them along the hiking trails. But because of the steep and tight nature of the site, that approach was soon abandoned in favor of setting the beams by air using with a helicopter.

Solley Crane Service, Decatur, AL, was selected as the helicopter service provider on the project. Established in 1972, Solley Crane Service was founded by Ray Solley. Initially, the company focused on concrete construction, but over time it began to shift toward the lifting arena. Today, Solley Crane Service has cranes working on projects in both North and South America.

Seeing an additional opportunity, Solley acquired its first helicopter in 1984 and added helicopter aircrane service to its already successful mobile crane business. Using Sikorsky twin turbine helicopters, the company has completed thousands of lifts for industrial and commercial customers in areas where other lifting options are not available.

On the day before the first beam was set, all members the team attended an FAA-mandated safety meeting.

"If you weren't at the meeting," Harrison says, "you could not be in the placement area. It was a simple as that."

Pilot's Eye View

On this project, Solley Crane Service utilized a Sikorsky S58 helicopter,piloted by Frank Barker and powered by twin turbines of 900 horsepower each, to lift and set the glue-lam beams.

Barker, who has been flying helicopters since 1984, explains that the beam placement operation staged from the park's parking area up on the rim of the canyon.

"After picking up a beam," he says, "I flew due west and straight down" to deliver the beam to the waiting bridge crews. Throughout the operation, the bridge crew maintained constant communication with the helicopter.

The first beam went in smoothly and without incident. The second beam, however, proved more of a challenge. A number of strategically placed trees interfered with the team's best efforts to position the beam, and after trying for a short while the beam placement operation was temporarily suspended while the construction team decided what to do.

"It was very congested in there," he says. And until that tree trimming was complete, he adds, "There was no way to snake the beams in without getting them hung up in the trees.

"In the end," Harrison adds, "we had to do some very selective tree trimming, taking out three trees to allow the beams to swing into place."

Once those trees were removed, he adds, beam placement went smoothly.

"Once we got going," Barker says, "I was able to average about seven to nine minutes per beam."

Adds Harrison, "He was able to place the remaining nine beams in about an hour and 20 minutes."

Overcoming Topographic Challenges

From the beginning, notes Harrison, the Cloudland Canyon bridge location was a challenging site — and much of that challenge came from the steepness of the terrain.

"We even had a tough time getting accurate topo mapping," he says, "because the elevation may change several feet over a distance of just a couple of inches."

But despite the extremely tough site, the bridge was completed on time this past spring. The final portion of the work involved construction of connector trails to existing trails on each side of the creek, and when it is complete the visitors to this northwest Georgia park were able to begin enjoying a new and most unusual bridge.

View photo gallery of this project, plus many other construction projects across the U.S. here.