Design methodology and input parameters applicable to foundation design for large complex towers

As buildings are progressively getting taller, traditional methods of design that generally relied on considerations of the vertical load-carrying capacity of the foundation system, assessed by empirical methods and a lumped factor of safety, have been largely replaced by serviceability-based methods of design which typically result in an optimised foundation design. Serviceability-based designs typically rely on powerful commercial software packages to enable advanced numerical analysis of foundation systems. This paper briefly discusses case studies of foundation design processes including soil-structure interaction analyses adopted for the serviceability design of tall towers. In order to obtain accurate building movement prediction from complex computer analysis, it is imperative that materials and ground stiffness properties be accurately characterised and measured. This paper presents ground stiffness properties measured from various types of tests at different strain levels (i.e., geophysical testing, pile load tests, pressuremeter and laboratory tests) that have been adopted as input parameters in the numerical analyses. The higher allowable shaft friction values from serviceability analysis compared to those from traditional methods, are further justified on the basis of bi-directional static pile testing.