East Area Sedimentation Basin
The City of Atlanta Department of Watershed Management had plans to repair and upgrade a stormwater containment tank to meet current standards and accommodate increased stormwater demands. Constructed in 1982, the tank featured 20-foot-tall concrete walls supported by piles, with footings buried more than five feet below grade. An additional four feet of excavation was required to expose a selected group of piles to accurately measure the existing piles and identify their material type. The challenge was to safely identify the type of piles used in the foundation to ensure the engineer of record could accurately design and support the structural upgrades to the tank.
United Consulting initially provided Ground Penetrating Radar (GPR) services to locate critical underground utilities essential for the facility’s continued operation. Heavy machinery and field engineering support were deployed to oversee and execute the excavation of a large hole measuring approximately 20 feet by 20 feet and 9 feet deep, adjacent to the distressed wall. To address safety concerns, our team of experts installed an automated monitoring system featuring a robotic total station that continuously tracked 10 prisms affixed to the existing wall. This system delivered data every 30 minutes, with real-time alerts sent to the project team if the wall movement exceeded 0.25 inch.
Our team of experts determined the excavated piles were encased concrete and measured their diameters. The concrete piles enable the city’s Engineer to reinforce the wall and floor slabs without requiring additional pile installation, significantly reducing repair costs of the tank. Data from the automated monitoring system confirmed that wall movement during excavation was negligible.
After backfilling the excavation, the city conducted a controlled test by diverting stormwater into the tank, filling it to approximately 16 feet. The automated monitoring system detected excessive lateral movement in the wall during the test and immediately triggered text and email alerts to the project team. In response, the team promptly decided to drain the stormwater, after which the wall’s lateral movement returned to zero. This provided a valuable opportunity to confirm that the piles could support the additional load without long-term settlement, with the observed wall movement attributed solely to elastic deformation.
