01-09-2014, 01:24 PM
EROSION CONTROL OF SOIL ON SLOPES
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INTRODUCTION
SOIL: - Soil is the material form of rocks by its chemical and physical disintegration.
Soil mechanics : - The branch which deals with soil and its nature and applications is
known as soil mechanics.
1. The field of soil mechanics is very vast the civil engineering has many device and
important encounters with soil, apart from the testing and classification of various
type of soil in order to determine its various physical properties.
2. The knowledge of soil mechanics is particularly helpful in following problems in civil
engineering.
The study of soil mechanics deals with :-
1. Foundation design and construction.
2. Pavement design.
3. Design of under ground structure and earth retaining structure.
4. Design of embankment and earth retaining structure.
5. Design of earthen dams.
EROSION OF SOIL
Because soil is formed slowly, it is essentially a finite resource. The severity of
the global erosion problem is only now becoming widely appreciated. The processes of
soil erosion involve detachment of material by two process, raindrop and flow traction
and transported by saltation through air or by overland water flow. Accelerated soil
erosion by water or wind may effect both agricultural areas and the natural
enviourmental and us one of the most widespread.
TYPES OF SOIL EROSION
GEOLOGIC EROSION OR NATURE EROSION
Is this action of the wind ,water ,ice & gravity in wearing away rocks to from soil
and shape and ground surface .Except for some .stream and shore erosion , it is a relatively
slow
ACCELERATED EROSION
Is this speeding up of erosion due to human activity whenever we destroy the
natural vegetation or alter the contour of the ground
SOIL EROSION BY WATER
Soil Erosion by water, may occur by water.
In the soil erosion by water makes the water and soil splashed….
Soil erosion by water is the result of rain ditching and transporting vulnerable soil,
either directly by means of rain splash or indirectly by rill and gully erosion…
Rain may move soil directly this is known as ‘rain splash erosion’ splash is only
effective if the rainfalls with sufficient intensity.. If it does, then as the raindrops hit
bare soil, their kinetic energy is able to detach and move soil particles a short
distance
Because, rains plash requires high rainfall intencities, it is most effective under
convective rainstorms in the world’s equatorial regions…
Soil erosion by wind
Soil erosion by wind may occur wherever dry, sandy or dustysurfaces, inadequately
protected by vegetation, are exposed to strong winds. Erosion involves the picking up and
blowing away of loose fine grained material within the soil. Damage from wind erosion
is of numerous types. The dust storms resulting therefrom are very disagreeable and the
land is robbed of its long-term productiviCrop damage, particularly in the seedling stage,
by blowing soil is often a major concern. Serious stand and subsequent yield and quality
losses are incurred and, in the extreme, tender seedlings may be completely killed. Often,
sufficient soil is removed to expose the plant roots or ungerminated seed, and this results
in complete crop failure. Covering of established crops or pasturage by drifting soil is
another common result. These are but a few of the more evident results of wind erosion.
Stability of slopes
Earth embankment are commonly required for railway,roadway and earthten dam
levees and river retaning works.
2. The failure of mass
3. It involves a downward and outward moment of the entire mass of soil that
participates on the failures .
4. The failure of slopes thake place mainly due to
1. The action of gravitation force
2. Seepage forces.
Every mass of soil which is bounded by a slopy surface is subjected to shering
stresses on nearly on its internal surfaces because of the gravitational forces which tend to
pull the upper portion of the mass downward towads a more nearly level surface. A slope is
an inclined boundary surface between air and the body of an earthwork such as highways, cut
or fill, railway cut or fill, earth dams, levees and river training works.
The stability of slope is one the most important one in civil engineering practice. A fairly
common engineering failure of slope is slipping of an embankment or cutting.
Stability analysis of finite slopes
Failure of finite slopes occurs along a curved surface. In stability analysis of finite slopes, the
real surface of rupture is replaced by an arc of a circle. As to the mode of failure, the slope
may fail basically in the following two ways:
a) The failure surface passing through the toe of the slope or above the toe of slope is known
as slope failure.
b) The rupture is deep seated and passes through the embankment supporting soil below the
toe of the slope is known as base failure.
EROSION OF LAND SLIDES
Erosion of soil due to landslides
A landslide is the gravitational movement of a mass of rock, earth or debris
down a slope. Landslides are usually classified on the basis of the material involved (rock,
debris, earth, mud) and the type of movement (fall, topple, avalanche, slide, flow, spread).
Thus, the generic term landslide also refers to mass movements such as rock falls,
mudslides and debris flows. Volcanic mudflows and debris flows are also called lahars.
Construction
1. Excavate to the required depth. The finished surfacing should be below the depth of
the surrounding ground or vegetation. The excavated depth should accommodate the
stones but finish the path at or below this level.
2. Do not excavate more than can be completed in one day. Two people can complete a
10 metre long section of a 1 metre wide route in one day.
3. Start on the downhill end of a section and work up the hill.
4. Dig in the Anchor Stone so that it is flush with the lower surface. The Anchor Stone
should be dug in as deep as possible.
5. Dig in the Pitching Stones, leaving the flattest surface upwards and at no more than 5
degrees from the horizontal. The rise between stones should be not more than 200
mm.
6. Butt adjoining stones against each other, wedging them in place using smaller stones
in the gaps. Use larger stones at the path edges to prevent lateral movement.
7. Compact excavate soil into gaps and crevices. Fertilise and reseed when appropriate.
A Brief History of Soil Nailing
Soil nail technology was first used in France to build a permanent retaining wall cut
in soft rock. The project, undertaken in 1961, was the first where steel nails were used to
reinforce a retaining wall. The first soil nail wall to use modern soil nailing techniques was
built near Versailles in 1972. The technique included installing high-density, grouted soil
nails into a 60-ft.-high wall and facing it with reinforced concrete. Since then, this technology
has improved to the point where soil nail construction is fast becoming the preferred method
of building soil retaining walls. Europe, particularly France and Germany, continues to lead
the world in soil nail technology.
Overview of the Soil Nail Process
Soil nailing is a method of construction that reinforces the existing ground. Passive inclusions
(the "nails") are inserted into the soil in a closely spaced pattern to increase its overall shear
strength. The nails are called "passive" because they are not pretensioned (as tieback
inclusions are); the nails develop tension as the ground deforms laterally in response to
ongoing excavation. In most cases, a temporary or permanent facing is added to retain the
soil. It should be noted that engineers and other experts familiar with this type of
construction must analyze the site and develop a site-specific nail placement design,
including their correct depth, angle, and frequency. This ensures that the structure can resist
the forces acting upon it and remain stable
Conclusion
1) Preventing soil erosion is an important task in order to keep the land fertile which can be
used for growing crops part. This situation is slowly reducing the net available land for
agriculture
2) To control the soil erosion helps to maintain the stability of the structure.
3) It also helps us, to avoid failure of the structure