Settlement-Control Piles to Optimize the Mat Foundation of a High-Rise Building in Downtown Orlando

A case history of a mat foundation enhanced with settlement-control piles to support a high-rise building in Downtown Orlando is presented. Column loads were substantially variable with a maximum load in excess of 13 MN. The original geotechnical studies recommended auger-cast-in-place piles to support the tower as well as the parking due to difficult soil conditions and highly variable loads. A value engineering study was performed by the authors. After few iterations of structural and geotechnical analysis, a mat foundation was recommended; however, the structural analysis resulted in high contact pressures at highly loaded columns and edges of the tower portion. The authors recommended adding settlement-control piles at specific locations to increase the mat stiffness, relieve the concentration of contact pressures, and reduce potential differential settlement. A pile load test was performed to verify stiffness of the settlement-control piles. Results of the structural analysis utilizing settlement-control piles showed lower and more uniform contact pressures. The results of the monitoring program confirmed the benefits of adding settlement-control piles to the mat. The system resulted in saving more than $1.0 million over conventional deep foundations and about 120 construction days.