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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #186465
Title: STUDY OF THE EFFECTS OF LATERAL SEEPAGE FORCES ON TENSION-CRACK DEVELOPMENT, BANK-FAILURE DIMENSIONS AND MIGRATION OF EDGE OF FIELD GULLIES

Author
item Simon, Andrew
item Wells, Robert - Rob

Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/4/2006
Publication Date: 4/4/2006
Citation: Simon, A., Wells, R.R. 2006. Study of the effects of lateral seepage forces on tension-crack development, bank-failure dimensions and migration of edge of field gullies. In: Proceedings of the 8th Federal Interagency Sedimentation Conference, April 2-6, 2006, Reno, Nevada, CDROM.

Interpretive Summary: Gullies represent a significant source of soil erosion. Prediction of the controlling processes and rates of gully erosion are still poorly understood. An edge-of-field gully along Goodwin Creek Mississippi was monitored with instruments to detect the processes that control gully migration. Repetitive surveys of the gully provided information on the amount and timing of erosion. Results show that gully migration is controlled by the interaction of several processes that lead to weakening of the soil mass by the build up of water within the soil mass and erosion at the base of the gully headwall. Gully migration by collapse of the headwall cannot occur unless previous erosion has occurred at the base.

Technical Abstract: Pore-water pressure is one of the most dynamic and important variables controlling geotechnical failure of streambanks and gully heads. The effects of positive pore-water pressures, matric suction and lateral seepage forces on streambank failures and edge of field gullies are being investigated at the Goodwin Creek Experimental Bendway, Mississippi. Nine nests of digital tensiometers were installed in a radial pattern at depths of 30, 100, 150, and 270 cm and spaced roughly 7, 60, 160, and 580 cm back from the gully head. Data are recorded at 10-minute intervals along with rainfall data from a tipping-bucket rain gage. Repetitive surveys of the gully head provide evidence of erosion events between February and September 2005. Results show that lateral seepage forces moving away from the gully face are greatest in the shallow (30 cm) zone closest to the gully face (7 - 60 cm) and generally decrease non-linearly with depth and with distance from the gully head. The vertical and horizontal distribution of these forces indicate a zone of strength that may determine failure-block dimensions during partial saturation of the soil mass. However, it is shown that mass failure of the headwall cannot occur unless the toe of the headcut has been previously undercut by hydraulic erosion or pop-out failures. Maximum seepage-force values of 13kN/m3 have been calculated, with values approaching zero at depths near 1.5 m. Infiltration via macropores and crack development behind the gully head may be important mechanisms in generating the positive pore-water pressures required for saturation and mass failure.