Reliability analysis of settlement for shallow foundations in bridges

The design of shallow foundations is becoming an attractive choice for supporting highway bridge structures. The settlement of structures built on soil is a subject of considerable interest to practicing engineers since excessive settlements can lead to serviceability problems or even failure states in the structural foundations. Therefore, the design of shallow foundations is most often governed by settlement requirements. A reliability-based approach can be applied for designing shallow foundations for which their design needs knowledge about the distribution of settlement under a given footing. The performance of geotechnical structures, including shallow foundations depends mostly on loads and soil properties, which are the random variables described by statistical parameters. However, most of the current research efforts have been focused on the reliability models for the superstructure components with less attention paid to the substructure and foundations. The random variables and limit state functions for shallow foundations are very different from those for superstructures such as bridges or buildings. The objective of this study is to develop the methodology for risk analysis procedures of shallow foundations. This requires development of the reliability models that can be applied to shallow foundations and involves the establishment of serviceability limit state functions. Reliability, as it can be expressed as a measure of structural performance, is expressed in terms of reliability indices, which in this research are calculated for total and differential settlement of shallow bridge foundations. The most important part of this study is the development of statistical models for total and differential settlements of shallow foundations on cohesionless soils by Monte Carlo simulations technique. This study verifies six settlement prediction methods for spread footing foundations by using compiled field data from research projects based on vertical settlements measured on 23 sites of footings for 12 highway bridges selected in US