United States Department of Transportation
i
Volumetric change of silts following cyclic loading.
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2013-06-01
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Soils and Geology
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Abstract:Estimating the settlement of adjacent structures during pile installation in silts is a challenging problem for
practicing engineers. The current state-of-practice relies primarily on local case studies and monitoring efforts, such as
inclinometers and site surveys, where adjacent structures are in relatively close proximity to pile driving activity. Few
predictive models exist to aid engineers, and those that do exist are limited to relatively “clean” sands and are rarely used
in practice. A very important aspect of pile driving are the shear waves that will be generated causing localized regions of
increased pore pressures resulting in significant reduction of soil strength and stiffness. Unfortunately, current practice
does not provide an engineer with any quantifiable means to estimate how these shear waves would affect the local soil
behavior.
The objective of this study was to perform a detailed review of the literature regarding pile driving-induced
settlements and to develop a laboratory testing program to quantify the relationship between cyclic loading, generation of
pore pressures, and the resulting volume changes in silts.In the first part of the present work a review of case studies and a
summary of settlement prediction methods are presented and the most important facts concerning those are highlighted.
The second part focuses on a series of cyclic triaxial tests carried out to evaluate volumetric change caused by pore
pressure dissipation of silt samples following cyclic loading. It was found that the greater the pore pressure ratio
generated during cyclic loading, the greater the volume changes of the silt sample resulting from pore pressure
dissipation. Cyclic loading and drainage caused a maximum of 5% volumetric strain in the silt samples, compared to less
than 1% for sands in comparable studies. The measured increase in volumetric strain was small up to a pore pressure ratio
of 0.6. The results of this research work supply important information on the behavior of volume changes of silt cyclically
loaded and provide a sound basis for future settlement predictions of silt due to dynamic loading.
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