The Mark at Atlanta
Offering posh student housing in an exciting urban setting, The Mark at Atlanta is a 27-story apartment building near Georgia Tech, Emory, and GSU. Schnabel was selected as the engineer of record for the design of a temporary support of excavation (SOE) system to enable deep basement excavation, including plans and specifications for the soldier pile and lagging embedded retaining wall.
Ground conditions at the site comprise fill overlying Piedmont residual soil (silty sands with mica), partially weathered rock (PWR), and gneiss bedrock. The wall had a maximum design retained height of about 35 feet. Various systems provided lateral support, including up to three rows of post-tensioned drilled and grouted ground anchors (tiebacks) that were required on three sides of the site. Where site constraints didn’t permit the use of tiebacks, steel pipe corner braces were used as well as steel H-pile raker sections embedded into cast-in-place concrete heel blocks. Where retained heights were modest, cantilever sections were designed to achieve economy.
We also designed micropiles for underpinning the existing spread footings on an adjacent building that was offset only five feet from the face of the SOE. We prepared geostructural engineering analyses and calculations for retaining wall earth pressures, wall stability, steel member sizing, and bearing plate weld connections. During construction, special inspections were undertaken during installation and load testing of non-production tieback anchors in order to verify the design assumptions for pullout capacity.
Design for ease of construction was achieved by using back-to-back MC channel sections for the soldier piles, enabling tiebacks to be installed between the webs. This innovative detail eliminated numerous waler beams, roll chocks, and the associated field welding that would have been required if conventional wide-flanged beams had been used. This feature saved time, reduced delay risk that arises when weather-dependent field welding is required, and improved safety.