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GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS

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* Stabilization by Geotextiles and Fabrics Geotextile which have very high tensile strength can be used ... Reinforced Earth Soil can be stabilized by introducing ... – PowerPoint PPT presentation

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Title: GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS


1
GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS
  • Guided by,
    Presented by,
  • Ms.Susan Rose
    Paul James

2
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.

3
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

4
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
    .

5
  • 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

6
  • 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.

7
  • 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.

8
  • 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.

9
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.

10
Fig vertical drains
11
  • 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.

12
  • 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 .

13
Fig Stabilizing trench
14
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

15
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
16
  • 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
17
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.

18
Fig Soil nail
19
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
20
(No Transcript)
21
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.

22
Fig vibro-compaction
23
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

24
Fig Dynamic compaction Equipment
25
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.

26
  • 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.

27
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.

28
Thank you..
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