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Published January 2018 | Supplemental Material + Published
Journal Article Open

The role of three-dimensional boundary stresses in limiting the occurrence and size of experimental landslides

Abstract

The occurrence of seepage-induced shallow landslides on hillslopes and steep channel beds is important for landscape evolution and natural hazards. Infinite-slope stability models have been applied for seven decades, but sediment beds generally require higher water saturation levels than predicted for failure, and controlled experiments are needed to test models. We initiated 90 landslides in a 5 m long laboratory flume with a range in sediment sizes (D = 0.7, 2, 5, and 15 mm) and hillslope angles (θ = 20° to 43°), resulting in subsurface flow that spanned the Darcian and turbulent regimes, and failures that occurred with subsaturated and supersaturated sediment beds. Near complete saturation was required for failure in most experiments, with water levels far greater than predicted by infinite-slope stability models. Although 3-D force balance models predict that larger landslides are less stable, observed downslope landslide lengths were typically only several decimeters, not the entire flume length. Boundary stresses associated with short landslides can explain the increased water levels required for failure, and we suggest that short failures are tied to heterogeneities in granular properties. Boundary stresses also limited landslide thicknesses, and landslides progressively thinned on lower gradient hillslopes until they were one grain diameter thick, corresponding to a change from near-saturated to supersaturated sediment beds. Thus, landslides are expected to be thick on steep hillslopes with large frictional stresses acting on the boundaries, whereas landslides should be thin on low-gradient hillslopes or in channel beds with a critical saturation level that is determined by sediment size.

Additional Information

© 2017 American Geophysical Union. Received 23 JUN 2017; Accepted 21 OCT 2017; Accepted article online 21 NOV 2017; Published online 9 JAN 2018. Brian Fuller helped greatly with the experimental design and instrumentation. Jabari Jones helped conduct several of the experiments. Our theoretical considerations benefitted from discussions with David Milledge, Richard Iverson, Bill Dietrich, Jose Andrade, Victor Tsai, and Jim Rice. This manuscript was improved following the thoughtful reviews of David Milledge, John Buffington, and an anonymous reviewer. Experimental data can be found in the supporting information. Funding for this work was provided by NSF grants EAR-0922199, EAR-1349115, and EAR-1452337; the Terrestrial Hazards Observation and Reporting center (THOR) at Caltech; and Uniscientia Stiftung through the ETH Foundation.

Attached Files

Published - Prancevic_et_al-2018-Journal_of_Geophysical_Research__Earth_Surface.pdf

Supplemental Material - 2017JF004410-sup-0001-Movie_20SI-S01_AA.avi

Supplemental Material - 2017JF004410-sup-0002-Table_20SI-S01_AA.doc

Supplemental Material - 2017JF004410-sup-0003-Movie_20SI-S02_AA.avi

Supplemental Material - 2017JF004410-sup-0004-Movie_20SI-S03_AA.avi

Supplemental Material - 2017JF004410-sup-0005-Movie_20SI-S04_AA.avi

Supplemental Material - 2017JF004410-sup-0006-Movie_20SI-S05_AA.avi

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