Performance of One Shell Plaza Deep Mat Foundation

The mat foundation for One Shell Plaza is 172 ft x 232 ft (52.46 m x 70.76 m) in plan, 8.25 ft (2.52 m) thick and 60 ft (18.3 m) below street level. The mat was designed using an iterative analytical procedure to include the effects of soil-mat interaction in determining foundation movements. To provide factual information on soil-structure interaction, the mat was instrumented to measure soil contact pressures and steel stresses. In addition, observations were made to determine total and differential mat movements. Performance observations during the 3-yr construction period and for about 6 yr since the structural frame was completed are examined and then compared in a limited way with design predictions.