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Erosion and Sediment Pollution Control Program Manual.pdf

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Water<br />

CAUSE<br />

Adapted from Terzaghi<br />

TRIGGERING<br />

PROCESS<br />

OR EVENT<br />

Rapid change<br />

of elevation of<br />

water table<br />

Rise of water<br />

table in distant<br />

aquifer<br />

Seepage from<br />

artificial source<br />

of water<br />

HOW THE<br />

FAILURE<br />

OCCURS<br />

14. Initiates<br />

rearrangement<br />

of grains<br />

15. Causes a rise<br />

of piezometric<br />

surface in<br />

slope-forming<br />

material<br />

16. Seepage<br />

toward slope<br />

17. Displaces air<br />

in voids<br />

18. Removes<br />

soluble binder<br />

19. Subsurface<br />

<strong>Erosion</strong><br />

MOST<br />

SENSITIVE<br />

MATERIALS<br />

Medium or fine<br />

loose s<strong>and</strong> in<br />

saturated state<br />

Silt or s<strong>and</strong> layers<br />

between or below<br />

clay layers<br />

Saturated Silt<br />

Moist, fine S<strong>and</strong><br />

Loess<br />

Find S<strong>and</strong> or Silt<br />

363-2134-008 / March 31, 2012 / Page 350<br />

PHYSICAL<br />

NATURE OF<br />

THE FAILURE<br />

Spontaneous<br />

increase of porewater<br />

pressure<br />

Increases porewater<br />

pressure<br />

Eliminates<br />

surface tension<br />

Destroys<br />

intergranular<br />

bond<br />

Undermines the<br />

slope<br />

EFFECTS<br />

UPON SLOPE<br />

EQUILIBRIUM<br />

Spontaneous<br />

liquefaction<br />

Decrease of<br />

frictional<br />

resistance<br />

Decrease of<br />

cohesion<br />

Increase of<br />

Shear Stress<br />

The Department provides this table as a guide only. Factors not contained in this table may influence<br />

slope stability in certain localities. It is incumbent upon the designer to employ due diligence in<br />

identifying those factors for the project site.

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