Seepage erosion mechanisms of bank collapse: Three-dimensional seepage particle mobilization and undercutting

G. A. Fox, M. L. Chu-Agor, R. M. Cancienne, G. V. Wilson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Seepage flow initiates undercutting, similar to development and headward migration of internal gullies, by liquefaction of soil particles, followed by mass wasting of the bank. Although seepage erosion has three-dimensional characteristics, two-dimensional lysimeters have been used in previous research to analyze for the hydraulic and geotechnical controls on this mechanism of hillslope, gully, and bank instability. A 50 cm cubic soil block with a focused inflow reservoir was constructed to investigate the mechanisms of seepage erosion and the three-dimensional nature of seepage undercutting. Experiments included 25-cm tall, sand and loamy sand soil blocks packed at prescribed bulk densities (1.30 to 1.70 g cm-3) and with an outflow face at various angles (90, 75, and 60 degrees). Constant heads of 15 cm, 25 cm, and 35 cm were imposed on the soil to induce flow. A laser scanner was utilized to obtain the three-dimensional coordinates of the bank and undercut surfaces at 15 to 30 s intervals. The bulk density for the two different soil types controlled which seepage failure mechanism occurred: (1) tension or "pop-out" failures due to the seepage force exceeding the soil shear strength, or (2) particle entrainment in the seepage flow, particle mobilization, bank undercutting, and bank collapse when the seepage force gradient was initially less than the initial resistance force of the soil block. For cases experiencing particle mobilization and undercutting, seepage erosion initiated as unimodal (i.e., concentrated at one point) or as multimodal (i.e., initiating at several locations across the bank face), largely controlled by the bank angle. As a first approximation, a three-dimensional, five-parameter Gaussian distribution was fit to the undercut shapes to derive parameters for the maximum depth of undercutting, position of the center of the peak, and the vertical and lateral spreads of the undercut.

Original languageEnglish (US)
Title of host publicationWorld Environmental and Water Resources Congress 2008
Subtitle of host publicationAhupua'a - Proceedings of the World Environmental and Water Resources Congress 2008
DOIs
StatePublished - Dec 1 2008
Externally publishedYes
EventWorld Environmental and Water Resources Congress 2008: Ahupua'a - Honolulu, HI, United States
Duration: May 12 2008May 16 2008

Publication series

NameWorld Environmental and Water Resources Congress 2008: Ahupua'a - Proceedings of the World Environmental and Water Resources Congress 2008
Volume316

Other

OtherWorld Environmental and Water Resources Congress 2008: Ahupua'a
CountryUnited States
CityHonolulu, HI
Period5/12/085/16/08

Keywords

  • River bank erosion
  • Seepage

ASJC Scopus subject areas

  • Management, Monitoring, Policy and Law
  • Water Science and Technology
  • Pollution

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