City: Atlanta
State: Georgia
Owner: New City Properties
General Contractor: Brasfield & Gorrie

BACKGROUND INFORMATION:
In 2017, commercial real estate developer New City Properties purchased 12 acres of land in the historic Old Fourth Ward (O4W) neighborhood in Atlanta, Georgia, with ambitious plans to build a mixed-use development on the property that will include office/apartment buildings, a hotel, a pedestrian bridge, an underground parking garage and much more. The city of Atlanta has become one of the fastest growing metropolitan areas in the United States, with the O4W neighborhood becoming a growing innovation hub attracting tech companies. Located to take advantage of this growth, the property is situated between the popular Atlanta BeltLine trail and Old Fourth Ward Park and in the vicinity of the trendy Ponce City Market mixed-use center.

In July of 2020, Brasfield & Gorrie, the general contractor at the 760 Ralph McGill Blvd project, engaged Schnabel to install a permanent excavation shoring system and several shotcrete foundation walls to facilitate the construction of a deep 1,250-space underground parking garage under the mixed-use site. In phases A and B of the project, Schnabel installed over 100,000 SF of permanent soil nail, rock bolt, and tieback shoring systems and more than 72,000 SF of permanent shotcrete foundation walls. Phase C of the project began in May of 2021, and during this phase, Schnabel installed 10,000 SF of permanent tieback shoring wall with permanent shotcrete facing. Schnabel’s earth retention work during these phases supported the construction of two 480,000 SQ FT office towers and a pedestrian bridge that connects the two office towers.

During this project, Schnabel installed a variety of walls, many in excess of 75 ft in depth. Challenges that came with performing such tall cuts included coordinating many tiers of soil nail and soldier beam/tieback walls with existing utilities and ongoing rock blasting as excavation progressed. Where soldier beams hit refusal above subgrade, Schnabel had to selectively redesign areas of the shoring wall as installation proceeded without delaying the overall project. Another challenge that Schnabel had to overcome was finding a way to install tiebacks around a large existing sewer trunk line. The sewer routes through the middle of the jobsite and had to stay active throughout the project and after completion. Furthermore, the city of Atlanta did not want any permanent tieback anchors installed above the sewer and impeding future maintenance. To address this issue, Schnabel’s R&D team proposed a creative design solution using Geofoam (expanded polystyrene) to reduce the earth pressure and position the tiebacks below the existing sewer. This helped the project team solve a tough problem at bid/ permitting time by accommodating the City’s requirement.