Erosion and Sediment Pollution Control Program Manual.pdf

TABLE 17.1
PROCESSES LEADING TO LANDSLIDES
TRIGGERING HOW THE MOST PHYSICAL EFFECTS
CAUSE PROCESS FAILURE SENSITIVE NATURE OF UPON SLOPE
OR EVENT OCCURS MATERIALS THE FAILURE
Changes state of
EQUILIBRIUM
1. Increase in All materials stress in slope- Increases shear
Slope Change Construction or height or
forming
stresses
Erosion
steepness of
materials
slope
Changes state of
Stiff, fissured clay; stress and Increases shear
shale
causes opening stresses and
2. Large-scale
of joints
initiates item # 8.
Tectonic Tectonic
deformations in All materials Increases slope Increases shear
Stresses Movements the earth’s crust
angle
Produces
stresses
All materials transitory Increases shear
change of stress stresses
Tectonic
3. High-frequency
Decreases
Stresses or Earthquakes or vibrations Loess, slightly Damages cohesion and
Explosives Blasting
cemented sand, intergranular increases shear
and gravel bonds
stresses
Medium or fine Initiates
loose sand in rearrangement Spontaneous
saturated state
Stiff, fissured clay;
of grains liquefaction
4. Creep on slope shale; remnants of
Reduces
Weight of Process which
old slides
Opens up closed cohesion,
Slope-forming created the 5. Creep in weak Rigid materials joints, produces accelerates item
Material slope
stratum below resting on plastic new ones # 8.
foot of slope ones
Water
Rains or
Melted Snow
Frost
Dry spell
Rapid
Drawdown
6. Displacement of
air in voids
7. Displacement of
air in open
joints
8. Reduction of
capillary
pressure
associated with
swelling
9. Chemical
weathering
10. Expansion of
water due to
freezing
11. Formation and
subsequent
melting of ice
12. Shrinkage
13. Produces
seepage
toward foot of
slope
Moist sand
Jointed rock, shale
Stiff, fissured clay
and some shales
Rock of any kind
Jointed Rock
Silt and Silty Sand
Clay
Fine sand, silt,
previously drained
363-2134-008 / March 31, 2012 / Page 349
Increases porewater
pressure
Causes swelling
Weakens
intergranular
bonds
Widens existing
joints, produces
new ones
Increases water
content of soil in
frozen top layer
Produces
shrinkage cracks
Produces
excess porewater
pressure
Decreases
frictional
resistance
Decrease of
cohesion
Decrease of
frictional
resistance
Decrease of
cohesion
Decrease of
frictional
resistance