Probabilistic analysis of settlements under a pile foundation of a road bridge pylon

Abstract

The paper addresses the reliability change of a road bridge pile foundation due to the unpredictable increase of settlements in time. The analysis is based on the Rędziński Bridge in Wrocław, Poland, its design assumptions, and monitoring results. The bridge foundation rests on a multi-layered subsoil assumed random. The Finite Element model of the subgrade is generated in ZSoil® software. To simplify the probabilistic approach, substitute soil strata stiffness parameters are adopted. Tracing their time decrement allows for a comprehensive definition of the entire foundation over-settlement produced by numerous factors. Preliminary sensitivity analysis of settlements to the stiffness variation properly simplifies the random model. The Serviceability Limit State helps to assess the foundation reliability index, further compared with the condition in the EN 1990:2002/A1:2005 standard. In addition, real-life settlements are also measured in the first year of bridge operation, they are used to calibrate the reliability index assessment. An innovative approach is proposed, where appropriate time-wise fluctuation functions represent the expected settlement increase and the related reliability reduction. These fluctuation functions help to plan the future remedial actions to maintain the initial bridge safety and to indicate the action frequency and scope. Future reliability levels may be extrapolated too. The real-life survey database of settlements makes it possible to validate the results of probabilistic calculations. A dedicated flowchart is devised to support further analysis of a wide structural domain.