ATLANTA, GA (October 26, 2016) – Batson-Cook Construction’s North + Line project in Atlanta’s Old Fourth Ward drew about 100 visitors to its site recently for an up-close look at the massive geotechnical construction phase in process in preparation for vertical construction of the mixed-use, multi-family redevelopment project.
North + Line is a $53.6-million project under way on 3.3 acres adjoining the former site of the Masquerade Club. Upon completion in April 2018, will include a five-story, 228-unit apartment building; a three-level, 240,000-square-foot secured parking deck with 467 spaces; street-level retail space; and elevated amenities. In order for vertical construction to begin, however, an existing 250-foot-long wall which supports the East Beltline Path 30 feet above its base must be stabilized and an additional 365 linear feet of new wall up to 43 feet high must be constructed. Hayward Baker, a specialty geotechnical construction contractor, is performing the work.
Members and guests of the Georgia Geo-Institute Chapter of the America Society of Civil Engineers, along with engineering students from Georgia Institute of Technology, met at the site recently to observe the stabilization project. Batson-Cook was the host, and Ryan Smith, project manager for
Hayward Baker, conducted an extensive safety briefing before leading the group on a site tour.
“Size alone makes this project unique,” Smith said, “but the fact that the existing wall has three distinct sections – one is stacked stone (rubble), a second is concrete, and the third is natural vegetation – is something else we rarely see.” Interest in the project also stems from its location on the former site of both the Masquerade Club, which has been relocated, and prior to that was an Excelsior manufacturing plant dating back to the 1890s, he added. It is generally thought that the stacked stone portion of the wall is of a similar age. The wall originally supported a once-active rail system, but is now part of the Atlanta Beltline multi-use trail system, which opened in 2012.
“On a scale of 1 to 10, this project is easily a 9 or 10 in difficulty,” Smith said. “Hayward Baker has 37 proprietary geotechnical techniques available to us, and we are using six of them on this job alone. It is a design-build project, and we worked through several design and price iterations over the course of a decade to determine the best solution.”
The major components of this mammoth undertaking were enumerated by Smith during the ASCI event:
• Top-down soil nailing of the natural vegetation section of the wall by excavating a 90-degree “cut” to create a new, stabilized wall extending upwards to 43 feet at its maximum height (17,100 square feet);
• Anchoring the existing concrete wall, then executing two different underpinning techniques to stabilize it (3,741 square feet);
• Soil nailing to stabilize the stacked stone wall (800 square feet);
• Installing vibro piers for the foundations of the apartment building and parking deck in areas with fine-grain soil.
A total of about 800 soil nails have been drilled into the expansive wall. Each “nail” is a one-inch-diameter bar set into a drilled six-inch-diameter hole which is then fill with grout. The nails at North + Line range from 15 to 45 feet in length and are set at a 15-degree angle to avoid grout leakage, Smith explained. Upon completion of the soil nailing work, the full length of wall was shotcreted for still greater stabilization.
Much of the wall will be hidden from view by the new apartment building and parking deck, but two sections will be visible from an outdoor deck, Smith noted. “We will employ two finishing techniques – screeded rubbed and rough gun bumped – to make those exposed areas aesthetically pleasing,” he said.
Jeremy Varner, chairman of Atlanta’s ASCE Geo-Institute chapter, expressed appreciation to Batson-Cook for inviting such a large group to tour an active jobsite. “This is a great repurposing of land around the beltline, and being allowed to see such a large geotechnical construction project in process really excites us as engineers.”
Owner of the project is SWHR PBL, LLC, and the architect is Smith Dalia Architects.