28-02-2011, 02:24 PM
presented by:
ARCHANA MALLICK
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Modern GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS
INTRODUCTION
Transportation contributes to the economic,industrial,social and cultural development of any country.
Transportation by road or highways is the only mode which could give maximum service to one and all.
When the soil on a project site cannot support the loads, ground improvement to increase strength, reduce compressibility, and enhance performance under applied loadings may be required.
The field of ground improvement techniques has been recognized as an important and rapidly expanding one.
Various methods are discussed below:
METHODS FOR GROUND IMPROVEMENT
1. VERTICAL DRAINS
2. SOIL NAILING
3. STONE COLUMNS
4. VIBRO COMPACTION
5. DYNAMIC COMPACTION
6. VIBRO PIERS
VERTICAL DRAINS
These consist of a column of pervious material placed in cylindrical vertical holes at sufficiently close spaces.
All drains should be connected at the ground surface to a drainage blanket.
Vertical drains accelerate consolidation by facilitating drainage of pore water.
Vertical drains are laid out in rows, staggered, or aligned to form patterns of equilateral triangles or squares.
Two types of drains are discussed below
SAND DRAINS
• A sand drain is a simple process, employing a column of at least 10 inches in width augered into ground to be surcharged and consolidated.
• The column is then filled with sand and connected to a free-draining blanket of granular soil.
WICK DRAINS
• A wick drain is usually about, 4 inches wide, 1/8-inch thick which acts as a high-permeability conduit for water to flow out of the soil and to the surface.
• Most common application of wick drains is for accelerating the settlement rate of compressible soils.
SOIL NAILING
This ground reinforcement process uses steel tendons which are drilled and grouted into the soil to create a composite mass.
A shotcrete facing is typically applied.
Soil Nailing is an in situ technique for reinforcing, stabilizing and retaining excavations and deep cuts.
Soil nailing is not practical in:
1. Soft, plastic clays
2. Organics/Peat
3. Fills (rubble, cinder, ash, etc.)
STONE COLUMNS
• Also known as vibro-replacement or vibro-displacement, is a ground improvement process where vertical columns of compacted aggregate are formed through the soils to be improved.
• The vibrator first penetrates to the required depth by vibration and air or water jetting or by vibration alone.
• Gravel is then added at the tip of the vibrator and progressive raising and repenetration of the vibrator results in the gravel being pushed into the surrounding soil.
• The soil-column matrix results in an overall mass having a high shear strength and a low compressibility.
VIBRO COMPACTION
It is a ground improvement process for densifying loose sands to create stable foundation soils.
The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular forces between the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 to 85 percent.
Compaction is achieved above and below the water table.