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Lecture#9
CE-312
Engineering Geology and Seismology
Instructor:
Dr Amjad Naseer
Department of Civil Engineering
N-W.F.P University of Engineering and Technology, Peshawar
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Outlines of the Presentation
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Landslides
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Causes of landslides
•
Landslides prevention
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Landslides
Loose materials slides down the slope because of gravity. The rate of movement
might of slow or fast depending on many factors. The movement of earth
materials can be classified into two major categories:
1. Earth flows, and
2. Landslides.
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Earthflow
The various types of earthflows are:
•
Soil creep
•
Rock creep
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Solifluction
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Mudflows
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Earthflow-Soil Creep
Soil Creep:
The continuous and slow movement of unconsolidated earth materials down the
slope is called soil creep. The rate of soil creep depends on:
•
Amount of rainfall,
•
Change in temperature,
•
Angle of slope,
•
Type of soil and,
•
Nature of parent material
The soil creep is indicated by the presence of tilted fence posts and curved tree
trunks, broken and displaced retaining walls etc.
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Earthflow-Rock Creep
Rock Creep:
The rock creep is the feature of jointed rock. The rock creep is present where a
joints or beds of the rock are exposed at the surface. The large joint blocks are
displaced by the rock creep. The slates or thinly bedded sedimentary rocks, if
exposed on a hillsides, often bend down slope and may show reversal of true
dip direction.
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Earthflow-Solifluction
Solifluction:
Solifluction is a type of creep which takes place in regions of cold climate where
the ground freezes to a considerable depth. During the summer the ground
thaws and the upper soil layer becomes saturated with water. This mass of
water saturated soil moves slowly downhill over the frozen materials at
greater depth.
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Earthflow-Mudflows
Mudflows:
In the mudflows, the movement of the earth is more rapid than the soil creep,
which usually follow old stream channels. Mudflows are produced in those
steep mountain areas where large amount of loose earth materials are available
and where abundant water is supplied by heavy rains or melting of snow.
Mudflows have destroyed buildings, roads, and useful land at many places in
semiarid regions.
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Landslides
Landslides:
When the earth body moves along a definite surface, the movement is called
landslides. This movement takes place under gravity and is facilitated by
moisture which acts as a lubrant agents. The slip surface is usually bounded
by a crack, which distinguishes a slide from creep in which a continuous crack
is often absent.
The important type of land slides are: slump, rock-slides and rockfalls.
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Landslides-Rock Slides
Rock Slides:
When detached blocks of bed rock move down the hill, it is called a ‘rock slide’.
In a rock slide the movement takes place on bedding planes, joints, or any
other planes of weakness in the country rocks.
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Landslides-Rock Falls
Rock Falls:
From Steep rock slopes, blocks of rock of varying sizes which are loosened by
weathering suddenly fall downwards under the influence of gravity.
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Prevention of landslides
Following are the prevention of landslides:
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Reducing slope,
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To prevent percolation of water
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Constructing retaining walls, pilling and concrete piers
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Consolidating the loose materials by cement grouting or any other cementing
materials.
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Causes of landslides
Following are the causes of landslides:
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Water: Water is the main factor in causing landslides. It acts in three ways:
1. Reduces cohesion,
2. It adds weight to the material, and
3. On freezing exerts an expansive force.
•
Nature of rocks: Landslides are more susceptible in rocks like clay, shale,
volcanic tuff, phyllite and mica-schist because these rocks are weak in
resisting shear.
•
Structure of rocks: joints, factures, shear zones and bedding planes usually
become the slip surface in case of rock slides.
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Causes of landslides
Disturbance of equilibrium: The existing equilibrium of the earth or rock mass
may be disturbed by:
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Over steepening of slope,
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Overloading of the upper part of the slope,
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Earthquake vibration and
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Increase in water content
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