Variability and Bias in Undrained Shear Strength from Different Sampling and Testing Methods
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 145, Issue 10
Abstract
Undrained shear strength is one of the most commonly used geotechnical design parameters for fine-grained soils. Disturbance produced during boring, sampling, and testing introduces an often unquantified and variable bias into undrained shear strength measurements, which in turn introduces bias and uncertainty into geotechnical design. Evaluations performed to quantify variability and bias in undrained shear strength determined using five different sampling and testing methods are described. The variability of undrained shear strength measurements differs considerably among sites, but is generally least for isotropically consolidated-undrained triaxial compression (CIUC) tests performed on high-quality specimens, slightly greater for unconsolidated-undrained triaxial compression (UU) tests performed on high-quality specimens, and greatest for unconfined compression (UC) tests performed on lesser-quality specimens and pocket penetrometer (PP) and handheld torvane (TV) tests. Quantitative bias determined for different sampling and testing methods is generally consistent with conventional wisdom regarding sampling and testing quality. The minimum achievable uncertainty for undrained shear strength is controlled by uncertain bias; coefficients of variation representing uncertainty are likely to be greater than 0.25 if sampling and testing methods that are inappropriate for a specific design application are used. Evaluations presented also suggest site-specific testing for shear strength parameters using stress history and normalized soil engineering properties (SHANSEP) techniques may reduce variability and uncertainty by approximately 10%–40% compared with using empirical estimates.
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Acknowledgments
A considerable number of faculty and students from the University of Missouri and Missouri University of Science and Technology, and numerous professionals from the Missouri Department of Transportation assisted with the site characterization and testing conducted for the three test sites considered in this work. The dedicated efforts of each of these individuals is gratefully acknowledged. The authors also greatly appreciate the objective, thorough, and thought-provoking comments provided by the anonymous reviewers of this manuscript. Funding for the work described was provided by the Missouri Department of Transportation, the Center for Transportation Infrastructure and Safety at Missouri University of Science and Technology, and the University of Missouri. The opinions, findings, and recommendations in this publication are not necessarily those of the Missouri Department of Transportation or the US Federal Highway Administration. This document does not constitute a standard, specification, or regulation.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 145 • Issue 10 • October 2019
Copyright
©2019 American Society of Civil Engineers.
History
Received: Jun 2, 2018
Accepted: Apr 8, 2019
Published online: Jul 31, 2019
Published in print: Oct 1, 2019
Discussion open until: Dec 31, 2019
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