A Comprehensive Comparison and Analysis of In-Situ Dynamic and Static Tests of a Cased Drilled Shaft

Abstract

This paper analyzes the undrained bearing capacity of temporary cased drilled shaft foundations installed as part of a new tower in Zagreb, Croatia. The comprehensive analysis focuses on skin friction resistance factors using in-situ static and dynamic test loading tests, a finite-difference computational model, and multiple semi-empirical bearing capacity equations. The cased drilled shafts support a 19-story tower on a layered deposit of soft, normally consolidated clay overlying stiff, normally to slightly overconsolidated Zagreb clays. Furthermore, the finite-difference simulations complement the dynamic testing to better understand the spatial and temporal evolution of the load transfer mechanism between the cased drilled shafts and adjacent soils during testing. Although many large-diameter piles have already been installed in Zagreb for buildings or bridge support, the skin friction resistance factors have not been fully understood in local clays, while full-scale in-situ testing has rarely been disseminated to a broader public. Therefore, the presented study will help guide future designs for cased drilled shafts in clays and contribute to global databases. In addition to exhibiting satisfactory bearing capacity in the tests performed as part of this study, the foundation raft system and the tower’s superstructure performed well during the 2020 Zagreb Mw5.3 and 2020 Petrinja Mw6.4 earthquakes.