GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS

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GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS

• Guided by,
  Presented by,
• Ms.Susan Rose
  Paul James

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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.

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METHODS FOR GROUND IMPROVEMENT

1. Soil stabilization
2. Vertical drains
3. Stabilization trenches
4. Capillary cut-off
5. Soil nailing
6. Stone columns
7. Vibro compaction
8. Dynamic compaction

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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
  .

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• 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

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• 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.

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• Bituminous Stabilization
• Bituminous stabilization provide water proofing
  and binding.
• Chemical Stabilization
• Stabilization by adding different chemicals.
• Electrical Stabilization
• Done by a process known as electro-osmosis.
• Stabilization by Grouting
• In this method grouting is done under pressure
  the stabilizers with high viscosity are suitable
  only for soils with high permeability.

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• Stabilization by Geotextiles and Fabrics
• Geotextile which have very high tensile strength
  can be used as reinforcement for strengthening
  soil.
• Reinforced Earth
• Soil can be stabilized by introducing thin strips
  in to it .
• Stabilization using Bio-Enzymes
• Bio-enzyme stabilization is a newer technique for
  strengthening of sub grade soil.
• Terra Zyme is one of the largely used bioenzymes.

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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.

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Fig vertical drains
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• 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.

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• 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 .

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Fig Stabilizing trench
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CAPILLARY CUT-OFF

• In some cases capillary water accumulates and
  saturates the subsurface layers which results in
  failures.
• To arrest this capillary rise, capillary cut-off
  has to be provided.
• Capillary cutoff is of two types.
• Permeable Capillary Cut-off
• Impermeable Capillary Cut-off

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Permeable Capillary Cut-off A layer of
granular material is provided which
has a thickness
higher than the capillary rise so that water
cannot rise above the cut-off layer
Fig-Cross-Section of pavement showing
Permeable capillary cut-off
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• Impermeable Capillary Cut-off
• An impermeable capillary cut-off is prepared
  by inserting bituminous layer in place of
  permeable blanket.

Fig Cross-Section of pavement showing
impermeable capillary cut-off
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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.

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Fig Soil nail
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STONE COLUMNS

• Done to provide adequate support for relatively
  light foundation.
• The method consists of forming vertical holes in
  ground which are filled with compacted crushed
  stone, gravel and sand or a mixture.

Fig stone columns
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(No Transcript)
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VIBRO COMPACTION

• For loose sand deposits, the density index can be
  increased by vibro compaction.
• This process employs a depth vibrator suspended
  from crane
• Compaction of sand can be achieved up to distance
  of 2.5m from axis of vibrator.
• Compaction can be carried out to significant
  depths up to 12m.

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Fig vibro-compaction
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DYNAMIC COMPACTION

• This involves in increasing the density of soil
  near the surface by tamping.
• Density improvement up to 10m is feasible.
• This method consists of dropping heavy mass of 8
  to 40 tonnes known as pounder on the surface from
  a height 5 to 30m

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Fig Dynamic compaction Equipment
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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.

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• Provision of capillary cut-off is effective for
  expansive soils.
• For soft and compressible soils provision of sand
  drains and sand wicks are found to be effective.
• Dynamic compaction is found suitable for soft,
  loose cohesionless soil layers..
• Stone column has also been found useful for soft
  soils.

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references

• Sanjay Kr Singh Pradeep Kr Gupta, (2002),
  "Critical review of ground improvement techniques
  for highways", Vol 30, No 8, Indian Highways,
  NewDelhi, pp. 5-13.
• Gaulkar.M.P, (1999), "Construction of roads III
  black cotton soils", Vol 27, No 3, Indian
  Highways, New Delhi, pp. 37-43.
• Sharma.S.C, (1994), "Ground Improvement
  Techniques", Vol. 22, No 12, Indian Highways,
  New Delhi, pp. 3-4.
• (1994), "Application of Geogrids in Highway
  Engineering", Special report 12, Indian Road
  Congress, New Delhi, pp. 59-61.
• Biju.P.B, Kuncheria.P.Issac, (2003), "Studies
  Stabilization Using TerraZyme for Pavement
  (M.Tech Thesis Report). on Soil Subgrade"
• Sharma.V.M. et.al, (2000), "Soil Nailing"
  ,Vol28, No 1, Indian Highways, New Delhi, pp.
  46-52.
• Arora.K.R, (2003), "Soil Mechanics and
  Foundation Engineering", Standard Publishers
  Distributors, Delhi.

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Thank you..