Foundation Geometry and Load Testing Reduces Uncertainty for a Sports Stadium

A special case study is presented to demonstrate the influence and evaluation of uncertainties involved in foundation design in geotechnical engineering. Site heterogeneity, variability in geometry, mechanical properties of bedrock, and seismic risk are the main sources of uncertainties considered. The subject structure is a new covered sports arena to be constructed in the Asian part of Istanbul, Turkey. The site is an old rock quarry and subsequently has been utilized as a landfill basin to accommodate soils and trash from various excavations within the city. Main lithological units underlying the upper uncontrolled fill are limestone, sandstone, and shale at varying locations and depths. Istanbul is seismically very active, and the planned structure for the sports arena is a dome supported on widely spaced columns. The high seismicity of the region combined with the very heterogeneous and poor subsoil conditions represent a big challenge for the decision process in design of foundations. Based on the various factors under consideration, it was decided to implement barrette foundations socketed in to the underlying bedrock to satisfy the specified vertical displacement-based performance criteria of the structure. The shear resistance of the socket interface was estimated during design stage using various empirical equations utilizing compressive strength of the bedrock. It was concluded that variability in lithology and mechanical properties of bedrock at various locations and depths results in a large range of unit skin friction values estimated, using various relations proposed, bringing further complication in the decision process in estimation of optimum socket length. O-Cell loading test procedure has been employed during design to verify and optimize the socket length.