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An exposed ground surface that stands at an angle with the horizontal is called slope.
Slopes are required in the construction of highway and railway embankments, earth
dams, levees and canals. These are constructed by sloping the lateral faces of the soil
because slopes are generally less expensive than constructing walls. Slopes can be
natural or manmade. When the ground surface is not horizontal a component of gravity
will try to move the sloping soil mass downwards. Failure of natural slopes (landslides)
and man-made slopes has resulted in much death and destruction. Some failures are
sudden and catastrophic; others are widespread; some are localized. Civil Engineers are
expected to check the safety of natural and slopes of excavation. Slope stability analysis
consists of determining and comparing the shear stress developed along the potential
rupture surface with the shear strength of the soil. Attention has to be paid to geology,
surface drainage, groundwater, and the shear strength of soils in assessing slope

Manmade slopes are used in:
River Training works
Slope Failure Triggering Mechanisms:
Intense Rain-Fall
Water-Level Change
Seepage Water Flow
Volcanic Eruption
Earthquake Shaking
Human activity
Causes of Slope failure:
1. Erosion: The wind and flowing water causes erosion of top surface of slope and
makes the slope steep and thereby increase the tangential component of driving force.
2. Steady Seepage: Seepage forces in the sloping direction add to gravity forces and
make the slope susceptible to instability. The pore water pressure decrease the shear
strength. This condition is critical for the downstream slope.
3. Sudden Drawdown: in this case there is reversal in the direction flow and results in
instability of side slope. Due to sudden drawdown the shear stresses are more due to
saturated unit weight while the shearing resistance decreases due to pore water
pressure that does not dissipate quickly.
4. Rainfall: Long periods of rainfall saturate, soften, and erode soils. Water enters into
existing cracks and may weaken underlying soil layers, leading to failure, for example,
mud slides.
5. Earthquakes: They induce dynamic shear forces. In addition there is sudden buildup
of pore water pressure that reduces available shear strength.
6. External Loading: Additional loads placed on top of the slope increases the
gravitational forces that may cause the slope to fail.
7. Construction activities at the toe of the slope: Excavation at the bottom of the
sloping surface will make the slopes steep and thereby increase the gravitational forces
which may result in slope failure.