Deterministic and probabilistic analyses of preload design at a hydraulic fill site

Selection of deterministic design soil parameters representative of insitu properties of soil is a difficult task in geotechnical engineering. Natural variability in soil as well as inadequacies in interpretation methods lead to large scatter in interpreted insitu parameters. The use of probabilistic methods to incorporate variability in soil parameters in preload design analysis is presented. A recent preload case history is used to illustrate this. The site consists of clayey and silty soils interlayered with fine-grained sandy silt and granular lenses. Initial evaluation of the interpreted coefficients of consolidation indicated large scatter by more than two orders of magnitude. The design was performed with deterministic methods using engineering judgement. The results from the initial deterministic design and the observed field performance data are compared with the results from a probabilistic reanalysis of the preload design. The influence of spatial variation of coefficient of consolidation, seams, and thin granular lenses within the clay deposit are incorporated in the reanalysis. The results highlight the usefulness of probabilistic methods in dealing with large scatter in soil parameters in design analysis.