Slope Angles in Friable Loess

Lohnes, R A; Handy, Richard L.

doi:10.1086/627327

Cited by 100 publications

(86 citation statements)

References 4 publications

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“…For the case of slabs with a water content of 50 per cent, the slab is unstable for all x < 0·62 m, regardless of the head, because thinner slabs are unstable even if water pressures bounding the slab are atmospheric. This value of x is identical to the value for loess slabs not affected by positive pore pressures (Lohnes and Handy, 1968). For large values of x up to 1·03, z c = 3·54-5·00 m.…”

Section: Earth Surface Processes and Landformssupporting

confidence: 71%

“…To do so, we use a simplified model of the gully banks in which a vertical tension crack of unit length strikes roughly parallel to the gully walls (Figure 10). Vertical tension cracks were commonly observed within 1-1·5 m of the gully prior to failure ( Figure 6A) and have been included in previous analyses of slope failures in loess and similarly cohesive sediments (e.g., Lohnes and Handy, 1968;Collison, 2001). …”

Section: Earth Surface Processes and Landformsmentioning

confidence: 99%

“…The vertical crack isolates a slab of loess alluvium supported at its base. The slab is unconfined, so Coulomb theory predicts failure to occur along a surface at its base at an angle, θ = 45°+ φ/2, from the horizontal, where φ is the soil friction angle (Lohnes and Handy, 1968). This two-dimensional model is a reasonable approximation if the distance between the gully and the tension crack, x, is small relative to the length of the crack.…”

Section: Earth Surface Processes and Landformsmentioning

confidence: 99%

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Bank‐collapse processes in a valley‐bottom gully, western Iowa

Thomas

Iverson

Burkart

2008

Earth Surf Processes Landf

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Widening and bank-slope reduction of a valley-bottom gully in western Iowa was correlated to increasing subsurface flow over a 36-year period. To study bank collapse at this gully, we measured rainfall, air temperature, hydraulic head near the banks and bank movement nearly continuously over a 2-year period. Styles of movement ranged from imperceptible creep to rapid slab collapses preceded by the formation of tension cracks parallel to the gully walls. Bank movement was commonly correlated to rainfall or snowmelt and associated head increases in the banks. If the banks are modelled as a twodimensional slab with an adjacent tension crack partly filled with water, measured heads were sufficient to cause bank failures through reduction of frictional support at the base of the slab. During winter months, air temperature variations across 0°C were correlated with bank movement: during mildly subfreezing periods banks expanded, and most, but usually not all, of this movement was recovered during above-freezing periods. This motion is attributed to frost heave followed by thawing. Deformation of the banks by heaving and thawing during winter may weaken them and prime them for failure during spring rains and snowmelt, when the frequency of mass-wasting events is highest.

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Section: Earth Surface Processes and Landformssupporting

confidence: 71%

Section: Earth Surface Processes and Landformsmentioning

confidence: 99%

Section: Earth Surface Processes and Landformsmentioning

confidence: 99%

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Bank‐collapse processes in a valley‐bottom gully, western Iowa

Thomas

Iverson

Burkart

2008

Earth Surf Processes Landf

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“…Lohnes and Handy (1968) applied Rankine-Bell earth-pressure theory along with equations developed by Terzaghi (1943) and presented a model to predict the recession distance of steep cohesive slopes without notching. Clean sands however, are cohesionless and as such a new approach based on the method presented by Lohnes and Handy (1968) was developed to predict failure of non-cohesive steep slopes affected by notching.…”

Section: Beam-type Mass Failure or Failure By Tensile Crackingmentioning

confidence: 99%

Laboratory investigation of beach scarp and dune recession due to notching and subsequent failure

2007

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Analytical models to calculate notch development and subsequent mass failure of dunes are presented. The notch evolution model is based on a transport equation for sediment from the dune and the sediment volume conservation equation, whereas the models of mass failure are derived using elementary engineering statics and soil mechanics. An empirical transport coefficient in the model describing the notch growth rate is found to be related to the hydrodynamic forcing at the dune normalized by geotechnical parameters describing the resistive strength of the dune. Two modes of mass failure are modeled whereby the overhang generated by the removal of material from the dune foot (notching) slides downward or topples over following the development of a tensile crack some distance shoreward of the maximum notch depth. The accuracy of the notch evolution and mass failure models are assessed by comparing calculated recession distances against measurements from a small-scale laboratory experiment.

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“…The borehole shear test device (Lohnes and Handy, 1968) is often used to measure cohesion and friction angle of in-situ soils. While this device is relatively inexpensive, it can be laborious to use, especially if a large number of measurements are required.…”

Section: Implications For Managersmentioning

confidence: 99%

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

Lammers

Bledsoe

Langendoen

2016

Earth Surf Processes Landf

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UNCERTAINTY AND SENSITIVITY IN A BANK STABILITY MODEL: IMPLICATIONS FOR ESTIMATING PHOSPHORUS LOADINGEutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the U.S. and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus budget of a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. Providing only single output values with no quantification of associated uncertainty can complicate management decisions focused on reducing bank erosion and nutrient loading to streams. To address this issue, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the USDA-ARS that simulates both mass wasting (stability) and fluvial erosion of streambanks. Sensitivity analysis results indicate that variable influence on model output can vary depending on assumed input distributions.Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non-cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress are relatively unimportant. However, the threshold effect of critical shear stress (determining whether erosion occurs) was not explicitly accounted for, ii possibly explaining the relatively low sensitivity indices for this variable. Model output distributions of sediment and phosphorus loading rates corresponded well to ranges published in the literature, helping validate both model performance and selected ranges of input values. In addition, a probabilistic modeling approach was applied to data from a watershed-scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates indicated that bank erosion was likely a significant source of sediment and phosphorus to the watershed in question, the uncertainty associated with these predictions indicates that they should probably be considered order of magnitude estimates only.iii ACKNOWLEDGEMENTS

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Slope Angles in Friable Loess

Cited by 100 publications

References 4 publications

Bank‐collapse processes in a valley‐bottom gully, western Iowa

Bank‐collapse processes in a valley‐bottom gully, western Iowa

Laboratory investigation of beach scarp and dune recession due to notching and subsequent failure

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

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