Stability of Steep Slopes in Cemented Sands
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 137, Issue 1
Abstract
The analysis of steep slope and cliff stability in variably cemented sands poses a significant practical challenge as routine analyses tend to underestimate the actually observed stability of existing slopes. The presented research evaluates how the degree of cementation controls the evolution of steep sand slopes and shows that the detailed slope geometry is important in determining the characteristics of the failure mode, which in turn, guide the selection of an appropriate stability analysis method. Detailed slope-profile cross sections derived from terrestrial lidar surveying of otherwise inaccessible cemented sand cliffs are used to investigate failure modes in weakly cemented [unconfined compressive strength ] and moderately cemented sands and their role in the evolution of the geometry of the slopes. The results show that high-resolution slope topography, such as can be obtained with terrestrial lidar, is essential for identifying altogether different failure modes in weakly cemented (shear-mode) and moderately cemented (tensile-mode) sand slopes. Analyses show that the standard Culmann method for steep slopes is inappropriate for modeling the stability of cemented sand slopes since it tends to overpredict expected crest retreat and underestimate failure plane angle. Instead, a simplified analysis using infinite slope assumptions, but applied to a slope with finite dimensions subject to changing geometric conditions, such as toe erosion and slope steepening, is suggested for analysis of weakly cemented sand slopes. For moderately cemented sand slopes, a limit equilibrium analysis directly comparing the cliff tensile stress and cemented sand tensile strength is shown to reasonably predict failure conditions and timing as a result of either slope steepening or tensile strength loss, presumably from wetting in most cases.
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Acknowledgments
Funding for initial stages of this research was provided by grants from the U.S. Geological Survey, Western Region Coastal and Marine Geology Team, the University of California, Coastal Environmental Quality Initiative (CEQI), and the U.S. Geological Survey, Mendenhall Postdoctoral Program. Reviews of initial drafts of this work by Jonathan Godt (USGS, Golden, Colorado) and Robert Kayen (USGS, Menlo Park, California) are gratefully acknowledged. We thank Joseph Labuz (Univ. of Minnesota) and four anonymous reviewers who provided important feedback on this paper upon submission.
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Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 137 • Issue 1 • January 2011
Pages: 43 - 51
Copyright
© 2011 ASCE.
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Received: Nov 2, 2009
Accepted: Jun 2, 2010
Published online: Jun 4, 2010
Published in print: Jan 2011
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