Washington State Department of Ecology
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slope modification

Slopes can be modified with regrading, geotextile mats, vegetation, and bioengineering
bioengineering

Unstable slopes can be modified to reduce the likelihood of a landslide, or to repair damage done by an existing landslide. Often, modification includes a combination of grading, retaining structures, drainage improvements, and revegetation.

Grading and excavation
One approach is to reconfigure the slope, excavating material from the top and reducing the overall slope. In some cases, the entire landslide mass can be removed. Such measures can be very effective where adequate space is available, but in many situations, particularly in developed areas or along shorelines, such options may be limited.

Geotextile mats and grids
Slopes can be directly strengthened in a number of ways without reshaping the entire hillside or resorting to retaining walls. An increasingly common method is the application of reinforced earth embankments in which grids or mats of geotextile are placed in horizontal layers (or lifts) and then packed with soil. This method allows steep slopes to be maintained and can permit significant revegetation - making it particularly applicable in areas of high aesthetic or environmental value. Such techniques are best suited for addressing shallow landslides and require substantial excavation of the existing slope.

Bioengineering and vegetation
Vegetation can also be used directly to help stabilize slopes using biotechnical methods, commonly referred to as slope bioengineering. These methods, originally pioneered in Europe, involve aggressive planting of carefully selected materials and the construction of engineered structures using live materials that will increase in strength over time. Vegetation can also be effective above steep slopes, where it intercepts precipitation, reducing both runoff and excessive infiltration. For more information on these techniques, see Controlling Erosion Using Vegetation.

Other techniques
Geotechnical engineers can draw on a range of additional techniques. Soil nailing involves drilling holes horizontally in the slope and anchoring long steel rods into them with concrete. Shotcrete (also called gunnite) is concrete sprayed onto a wire mesh, somewhat like paper maché, to protect a slope from water and erosion.
Shotcrete on a slope.
 
online resources
Free erosion control information

See Controlling Erosion Using Vegetation for more information. "Slope Stabilization and Erosion Control Using Vegetation: A Manual of Practice for Coastal Bluffs" is also available in print.
controlling erosion using vegetation
 
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