Determination of the scale of fluctuation of cone penetration test data obtained from an alluvial site in Missouri
To account for uncertainty in geotechnical projects, knowledge of the uncertainties should be understood. Many sources of uncertainties can be reduced with increased sampling and good practices, but due to the nature of geomaterials, inherent uncertainties cannot be eliminated. Inherent uncertainties can be quantified by a statistical analysis. While some statistical descriptors, such as mean and standard deviation are common, the scale of fluctuation is less studied as it requires a large amount of data. The scale of fluctuation indicates the thickness of a soil layer which has correlated properties. Large quantities of data can be obtained from the cone penetration test (CPT). The CPT was used for a site investigation for a coal combustion residual landfill, providing ideal measurements to investigate the variability of the alluvial site on the Missouri River. The goal of Sutton's thesis is to determine if side resistance measurements, reported as the friction ratio, of cone penetration testing are less correlated than cone tip resistance measurements as previous research indicates. The results of this analysis agree with earlier analyses that the variability of the cone tip resistance is less than the skin friction. The average vertical scale of fluctuation for the cone tip resistance was 1.3 feet and 1.5 feet for sand and gravelly sand, respectively. The average vertical scale of fluctuation for the friction ratio was 0.7 feet and 0.8 feet for the sand and gravelly sand, respectively. As increased computing power allows more complex modelling to become readily available, the shift to probabilistic analyses of such models allows for a more realistic assessment of the variability and correlation of subsurface properties. Several examples are discussed with show the effect of correlation and illustrate the need for both typical and site specific probabilistic parameters.
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