2. An exposed ground surface that stands at an
angle with the horizontal is called slope
INTRODUCTION
What is a slope?
What happens if slope fails?
3. Types of slopes
Natural:
Formation due to geological features of the earth
Man made:
Formed for construction activity like
embankments, cuttings etc.,
Examples
Hill sides and valleys
Coastal and river cliffs
Examples
Cuttings and embankments for
highways and roadways
Earthen dams
Temporary excavations
Waste heaps (landfill slopes)
Landscaping for site developments
4. Types of slopes
Hill side Valley side Cuttings Embankments
River cliff Landfills Landscape Earthen dam
5. Infinite slopes:
They have dimensions that extends over
great distances and the soil mass is
inclined to the horizontal.
Finite slopes:
A finite slope is one with a base and top
surface and the height is limited.
The inclined faces of earth dams,
embankments and excavations are some
examples of finite slopes
6. • Failure of slopes is catastrophic and results in significant loss to the lives and
properties.
• Civil engineers are expected to check the safety of soil slopes.
• Slope stability consists of determining and comparing the shear stress developed
along the potential rupture surface with the shear strength of soil.
• Attention must be paid to geology, surface drainage, ground water and shear
strength of soils in assessing the slope stability.
Why to bother about soil slopes ?
7. Erosion
Steady seepage
Sudden drawdown
Intensive rain fall
Earthquakes
External loading
Rise of ground water table in the sloping region
Construction activities
Geological features
CAUSES OF SLOPE FAILURES
8. 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
Steady seepage: Seepage forces in the sloping direction add to gravity forces and makes the slope
susceptible to instability. The pore water pressure decrease the shear strength. This condition is
critical for the downstream slope.
Sudden drawdown: Sudden reduction in water level due to sudden drawdown has two effects:
reduction of the stabilizing external hydrostatic pressure and changes in the internal pore water
pressure
Rainfall: Rainfall for a long duration saturate, soften and erode soils. Water enters into existing
cracks and may weaken underlaying soil layers and leads to slope failure.
CAUSES OF SLOPE FAILURES
9. Earthquakes: They induce dynamic forces. In addition to that, there will be sudden increase in the
pore water pressure, which reduces available shear strength.
External loading: Additional loads placed on top of the slope increases the gravitational forces
that may cause the slope to fail.
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.
CAUSES OF SLOPE FAILURES
10. TERMINOLOGY Slip or failure zone: It is a thin zone of soil that reaches
the critical state or residual state and results in
movement of upper soil mass
Slip plane or failure plane or slip surface or failure
surface:
It is the surface of sliding
Sliding mass:
It is the soil within the slip plane and the ground
surface.
Slope angle:
It is the angle of inclination of a slope to the horizontal.
12. Face (slope failure):
This type of failure occurs
when the slope angle is large
and when the soil at the toe
portion is strong
Toe failure:
In this case, the failure surface
passes through the toe. This occurs
when the slope is steep and the soil
is homogeneous
Base failure:
In this case, the failure surface
passes below the toe. This generally
occurs when the soil below the toe is
relatively weak.
TYPES OF SLOPE FAILURES
