Opening ceremony shaft for the Athens 2004 Olympic Games

Key aspects of the analysis, design and construction of the retaining structure for a central circular shaft inside the Olympic Stadium of Athens are described. As part of the opening ceremony of the Athens 2004 Olympic Games, the shaft was used as an invisible underground entrance into the stadium, playing a key role in the ceremony. Given the significant depth and the large diameter of the shaft (both about 25 m), excavating and retaining under extreme time constraints and with presumed high water table constituted a challenge. It was accomplished with recourse to the observational method. The retaining structure comprised 1·2 m diameter contiguous piles capped with a ring beam. The initial design used a form of top-down construction of the final 0·75 m thick permanent concrete lining. Delays in starting the excavation necessitated that a depth of 17·5 m be reached before any permanent lining could be constructed. The paper presents the design of the retaining structure, the developed finite element analysis, and the theoretical predictions during the various excavation stages. A detailed monitoring programme was implemented and utilised in the spirit of the observational method. Comparisons every two days of measured against original (class A), as well as updated, analytical predictions led to the successful completion of the project.