Ground_Improvement_Techniques

7/29/2019 Ground_Improvement_Techniques

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GROUND

IMPROVEMENT

TECHNIQUES


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GROUND IMPROVEMENTThe methods which are capable of

improving certain characteristics of

soft ground for civil engineering

constructions are all considered as

ground improvement techniques.


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GROUND IMPROVEMENT

TECHNIQUES

Mechanical Stabilization

Chemical Stabilization Thermal Modification Methods

Hydraulic Modification

Reinforcement Method

Grouting


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MECHANICAL

STABILIZATION1. Vibro Compaction

2. Vacuum Consolidation

3. Preloading


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1. Vibro-Compaction

1. Rearrangement of soil particles intodenser configuration by use ofpowerful depth vibration.

2. A ground improvement process fordensifying loose sands to create stablefoundation soils.3. It is performed with specially

designed vibrating probes. After probereaches required depth, a granularmaterial such as sand is added to fillvoid spaces created by vibrator.


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Applications

Reduction of foundation settlements.

Reduction of risk of liquefaction due

to seismic activity.

Permit construction on granular fills.


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2. Vacuum Consolidation

1. Effective means for improvement ofsaturated soft soils. The soil site iscovered with an airtight membrane and

vacuum is created underneath it byusing dual venture and vacuum pump.

2. It can provide equivalent preloadingof about 4.5m high conventional

surcharge fill. Soil is preloaded byreducing pore pressure whilemaintaining constant total stress.


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Applications

Replace standard pre-loading techniqueseliminating the risk of failure.

Combine with a water pre-loading in scare fillarea. The method is used to build largedevelopments on thick compressible soil.

Combine with embankment pre-load using theincreased stability


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3. Preloading

1. Process of placing additional verticalstress on compressible soil to removepore water over time.

2. The pore water dissipation reducestotal volume causing settlement.

3. Due to its time dependent nature,delaying projects make it a non-feasible aternative.


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Applications

Reduce post-construction Settlement

Reduce secondary compression.

Densification

Improve bearing capacity


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CHEMICAL STABILIZATIONImproving the engineering properties

of soils used for pavement base

courses, sub base courses, and

subgrades by the use of additives

which are mixed into the soil to effect

the desired improvement.


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Additives Used :

LimeLime can be used to treat soils in order toimprove their workability and load-bearingcharacteristics in a number of situations.Quicklime is frequently used to dry wetsoils at construction sites and elsewhere,reducing downtime and providing animproved working surface. An even moresignificant use of lime is in the

modification and stabilization of soilbeneath road and similar constructionprojects. Use of lime can substantiallyincrease the stability, impermeability, andload-bearing capacity of the subgrade


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Portland Cement

A cement-modified soil (CMS) is a soilmaterial that has been treated with a

relatively small proportion of Portland

cement. The objective of the treatment

is to amend undesirable properties ofproblem soils or substandard materials

so that they are suitable for use in

construction. The amount of cement

used will dictate whether modificationor stabilization has occurred.


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Fly Ash

A chemical additive consisting mainly

of silicon and aluminium compounds,

is a by- product of combustion of coal.

It is mixed with lime and water toproduce hard cement like mass. Its

role in stabilization is to act as

pozzolan or as a filler material to

reduce air voids.


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Calcium Chloride

It is a chemical additive that has ability toabsorb moisture from air until it liquifies

into a solution. Its presence in moisture

of soil lowers its freezing temperature.

For this reason, calcium chloride isproven stabilizing additive for cold

climatic conditions. If water in soil cant

freeze, there is less soil movement (i.e,

frost heave) making it much more stable.


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Bitumen

Bitumen is a mechanical additive thatoccurs naturally or as a by-product of

petroleum distillation. Bitumen makes

soil stronger and resistant to water and

frost. The use of bitumen can lead tofewer weather related delays during

construction and makes compaction

easier and more consistent.


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THERMAL MODIFICATION

METHODS

1. Heating

2. Ground Freezing


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1. Heating

1. Breaks the soil particle down to form a

crystalline or glass product.

2. Permanently alters the properties ofsoil.

3. Temperature can range between 300 to

1000 degree celsius depending upon the

type

of soil.

4. Impact on adjacent structures and

utilities


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Applications

Immobilization of radioactive orcontaminated soil

Densification and stabilization


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2. Ground Freezing

1. Use of refrigeration to convert in-situ

pore water to ice.

2. The ice acts as cement or gluejoining together the adjacent particles

of

soil or blocks of rocks to increase their

combined strength and make them

impervious


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Applications Temporary support for an excavation Prevention of groundwater flow into

excavated area

Temporary slope stabilization

Temporary containment oftoxic/hazardous wastecontamination


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HYDRAULIC MODIFICATION

Free excess water is removed from the

soil by providing vertical drains such as

Sand Drains


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Sand Drains

1. Sand drains are installed under a

surcharge load to accelerate drainage

of impervious soil and thus speed up

consolidation.2. These drains provide shorter path

for water to flow through to get away

from soil.

3. Time to drain clay layers can be

reduced from years to couple of

months.


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Applications

1. In treatment of soils having highwater content and low permeability

2. Used in consolidation of extensiveareas of loading such as airport

runways, reservoirs, etc.


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REINFORCEMENT METHOD

Vertical Reinforcement- Piles, Stone

Columns Horizontal Reinforcement- Soil

Nailing, Geo-Synthetic Products


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1. Piles

1. Small diameter piles capable of

sustaining

high loads.2. Drilling equipment and method allows

Drilling through virtually every ground

condition, natural and artificial, withminimum

vibration, disturbances and noise, at any

angle

below horizontal.


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Applications For structural support and stability.

Foundations for new structures.

Repair/Replacement of existingfoundations

Arresting/Prevention of movement Soil strengthening and protection


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2.Stone Columns

1. Columns of dense, crushed stone designedto increase bearing capacity and reducesettlement.

2. Useful for cohesive and layered soils.

3. Provide efficient drainage path for pore waterpressure dissipation.

Two methods of stone column construction

(i) Top feed method

(ii) Bottom feed method


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(i) Top feed method

In this technique, jetting water is usedto remove soft material, stabilize the

probe hole, and ensure that the stone

backfill reaches the tip of the vibrator.


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(ii) Bottom feed method

It uses the same vibrator probes as top

feed method, but with the addition of a

hopper and supply tube to feed the

stone backfill directly to the tip of the

vibrator.


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Applications

Reduction of foundation settlement

Impove bearing capacity/ Reduce

footing size requirements

Slope stabilization Permit shallow footing construction


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3. Soil Nailing

1. As a remedial measure to treat

unstable natural soil slopes or for allowing

safe over steepening of new and existing

soil slopes.

2. It involves insertion of relatively slender

reinforcing elements into slope.

3. A rigid facing or isolated soil nail platesmay be used at surface. A flexible

reinforcing mesh may be held against soil

face.


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Applications Stabilization of rail and highway cut

slopes. Excavation returning structures for highrise buildings and underground facilities.

Existing structures such as failing retaining

walls and bridge abutments to provide longterm stability without demolition and rebuildcosts.


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Basic Functions Drainage : Collecting and redirecting

seepage water within a soil mass oradjacent to retaining wall culverts andtunnel linings.

Filtration : Allows seepage from waterbearing layer while retaining soil particles.

Separation : Prevents mixing of adjacentdissimilar soils during construction orrepeated external loading.

Reinforcement : Inclusion of fabric toprovide tensile strength, redistribution ofstresses increasing stability of soil massand reducing earth pressure.


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Applications

In pavements on soft soils for increasingbearing capacity.

In rails to prevent ballast contaminationand distribute load on subgrade.

In embankments to improve stability andprovide drainage.

In retaining structures to reinforce andprotect backfill.

On natural slopes to protect againsterosion.

In rivers and reservoirs, to improvetraditional filter layers and for erosion

control.


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GROUTINGInjection of special liquid or slurry

material called grout into ground for

purpose of improving soil or rock.

Grouting Methods

Intrusion grouting

Permeation grouting

Compaction grouting

Jet grouting


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Intrusion grouting

Consists of filling

joints or fractures with

grout

Primary benefit is

reduction in hydraulicconductivity

Used to prepare

foundation and

abutments for dams

Usually done using

cementitious grouts


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Permeation

grouting

Injection of thin grouts

into the soil

Once the soil cures,

becomes a solid mass Done using chemical

grouts

Used for creatinggroundwater barriers or

preparing ground

before tunnelling


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Compaction

grouting When low-slump

compaction grout is

injected into granular

soils, grout bulbs areformed that displace

and densify the

surrounding loose soils.

Used to repair

structures that have

excessive settlement


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Jet grouting

Uses a specialpipe with horizontal

jets that inject grout

into the ground at

high pressures. An erosion/

replacement system

that creates an

engineered, in situ

soil/cement product

known as Soilcrete.


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THANK YOU

Presented By

Abhishek Koul

0909003

Submitted to

Mrs. Aarti Chouksey

Astt. Prof.

Civil Engg. Deptt.

Ground_Improvement_Techniques

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