Soils 497A Urban Soils

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Soils 497AUrban Soils

• Landscape Stability 2
• Slopes

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Expression of Slope

• Typically, Civil Engineers and Landscape
  Architects use a ratio of linear horizontal units
  to units of vertical distance. (21, 31).
• Soil Scientists use the percent slope that is the
  change in elevation divided by the change in
  distance.
• Geologists and Engineers also use degrees of
  slope. The angle of the slope.

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Slope Stability

• The slope must be internally stable in the
  engineering sense which is much deeper than the
  usual planting soil.
• Slopes must be stable prior to the establishment
  of vegetative cover.
• Vegetation only will stabilize the slope down to
  the depth of the roots, not any deeper.

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Angle of Repose

• In Engineering circles, it might be called angle
  of internal friction.
• Most soils have a stable angle of repose between
  30 and 40 degrees.
• Angle of Repose is often overlooked during
  construction causing slippages.

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This soil has been piled steeper than its
inherent angle of internal friction.
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Slope Failure
Topography
Internal Factors

• Soil Thickness
• Bedrock Type / Orientation
• Water Drainage Paths
• Watertable Depth

• Slope Gradient
• Slope Length
• Slope Shape

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Topography
Which slope shape will have a better chance to
develop an unstable slope?
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Slope Stress
The internal angle of friction of the soil
defines the slope at which that soil is stable.
Shear
Normal
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Rotational Slides
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Collapse Zone
Funnel Zone
Run-out Zone
Italy
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Collapse Zone
Funnel Zone
Run-out Zone
La Conchita, CA courtesy of USGS
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Town of Onondaga, NY
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Colorado
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Courtesy of USGS
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Creating parallel ridges to provide teeth for the
soil to adhere to.
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Creating terraces to provide teeth for the soil
to adhere to.
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THE ENGINEERED SLOPE AS APPLIED TO THE GETTY
CENTER, VIEW 1
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THE ENGINEERED SLOPE AS APPLIED TO THE GETTY
CENTER, VIEW 2
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Use of Geofibers to help stabilize the designed
soil slope.
Carnegie Mellon University Krause Campo
Sculpture Garden Pittsburgh, PA
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Transition from designed soil to in-situ soils.
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Transition from designed soil to in-situ soils.
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Drainage Location for Retaining Walls
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Gravel Trench with Tile Line to intercept errant
water.
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