Scale of Fluctuation of Geotechnical Parameters Estimated from CPTu and Laboratory Test Data

For a complete probabilistic characterization of a geotechnical parameter, its mean, variance, and the scale of fluctuation have to be known. While the mean and variance can be easily determined, determination of the scale of fluctuation is a little more complex. Knowledge of the scale of fluctuation is important in reliability-based design as it is used in implementing spatial averaging and computing the variance-reduction factor. Published values of scale of fluctuation of geotechnical parameters are based on widely sourced data and hence may not be most appropriate for local situations. Based on 11 CPTu soundings and laboratory test results of fine-grained soils from 15 boreholes at four different locations in Missouri, this paper uses the semi variogram function to determine the scale of fluctuation of geotechnical parameters. Owing to scale of fluctuation being dataset-dependent, differences between published values and the Missouri values determined in this study were observed. Spatial averaging effect, depending on magnitude of the reduction in variance of parameters, can potentially lead to a more optimal and cost-effective design

Influence of Geotechnical Dataset on the Range of Influence of Undrained Shear Strength

The knowledge of the spatial variability of geotechnical parameters, which can be described statistically by the mean, the variance, and the scale of fluctuation, is important in reliability-Based design. of particular importance is the scale of fluctuation. It can be used to compute the variance reduction factor, a factor of spatial averaging of geotechnical properties to reduce their point variance. the most prevalent method of determining the scale of fluctuation uses datasets whose data points are at close and regular intervals, e.g. measurements from cone penetrometer soundings. Another method, when continuous measurements are not available, uses datasets that are widely spaced and at irregular intervals. Presented in this paper is a comparison of the range of influence of the undrained shear strengths at three different locations in Missouri determined from continuous and regularly spaced CPTu data and the non-continuous and irregularly spaced Shelby tube sampling data. © 2011 ASCE