07-02-2010, 08:03 PM
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GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS
INTRODUCTION
Transportation - needed for the development of the country.
The main mode of transportation is by road or highways.
In the process of road development, the alignment of road may have to be fixed through the soils which may not bear the traffic loads .
There are various techniques of ground improvement.
METHODS FOR GROUND IMPROVEMENT
Soil stabilization
Vertical drains
Stabilization trenches
Capillary cut-off
Soil nailing
Stone columns
Vibro compaction
Dynamic compaction
SOIL STABILIZATION
Improvement of stability or bearing capacity of soil by use of controlled compaction or by the addition of suitable admixtures or stabilizers .
There are various methods of soil stabilization .
The methods of soil stabilization are:
Mechanical Stabilization
Soil-cement Stabilization
Soil-lime Stabilization
Soil-bitumen Stabilization
Chemical Stabilization
Electrical Stabilization
Stabilization by grouting
Stabilization by geotextile and fabrics
Reinforced earth
Using bioenzymes
Mechanical Stabilization
Process of improving the properties of soil by changing its gradation.
Two or more natural soils are mixed to obtain a composite material.
Cement Stabilization
Done by mixing soil and cement with water and compacting the mix to attain a strong material.
Lime Stabilization
Lime stabilization is done by adding lime (2%-10%) to soil.
VERTICAL DRAINS
Act as free draining water channel. surrounded by a thin filter jacket which prevents the surrounding soil from entering the core.
A vertical sand drain accelerates the rate of consolidation.
Installation of vertical sand drains is a convenient technique for stabilization of soft and compressible soil .
There are two types of vertical drains - sand drains and sand wicks.
Sand drains
Typically 200-500 mm in dia.
Formed by infilling sand in to a hole in the ground.
Hole formed by driving ,jetting or augering.
Typical spacing 1.5 - 6.0 .
Sand wicks
Sand wicks are improved technique of sand drains.
A small diameter hole is made by driving mandrel or by boring.
Then cylindrical bag with sand is lowered into this.
STABILIZING TRENCHES
Excavation which has a blanket of filter material between 0.5m and 1.00 m thick against its upstream slope and at the bottom of system for collecting and eliminating water.
Improves the stability of embankment by providing drainage and replacing weaker material with better material .
SOIL NAILING
Earth retention structure that combines reinforcements and shortcrete to support excavations , hillside , embankment steeping etc¦
The nails must have bending stress. The tension developed in nails provides resisting forces which stabilize the soil mass.
CONCLUSIONS
While constructing highways different ground conditions are encountered. Considering all factors a suitable ground improvement technique has to be done. Ground improvement techniques have been extensively used by developed countries.
Lime stabilization is suitable for expansive soil like black cotton soils.
In bitumen stabilization optimum content of bitumen vanes from 4 to 6 % soil.
Electrical and Chemical stabilization are expensive compared to others.
Stabilization by grouting is suitable only for soils with high permeability.
Stabilization by Terra Zyme is most effective for fine grained soil.
