Download - Session 7 Soil Stabilization
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The soil stabilization means the improvement of stability or bearing power of the soil by
the use of controlled compaction, proportioning and/or the addition of suitable admixture or
stabilizers.
Basic Principles of Soil Stabilization.
Evaluating the properties of given soil
Deciding the lacking property of soil and choose
effective and economical method of soil stabilization
Designing the Stabilized soil mix for intended
stability and durability values
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Limited Financial Resources to Provide a complete
network Road System to build in conventional
method
Effective utilization of locally available soils and
other suitable stabilizing agents.
Encouraging the use of Industrial Wastages in
building low cost construction of roads.
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Mechanical Stabilization
Soil Cement Stabilization
Soil Lime Stabilization
Soil Bitumen Stabilization
Lime Fly ash Stabilization
Lime Fly ash Bound Macadam.
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This method is suitable for low volume roads i.e.
Village roads in low rainfall areas.
This method involves the correctly proportioning
of aggregates and soil, adequately compacted to
get mechanically stable layer
The Basic Principles of Mechanical Stabilization
are Correct Proportioning and Effective
Compaction
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Adequate Strength
Incompressibility
Less Changes in Volume
Stability with Variation in water content
Good drainage, less frost Susceptibility
Ease of Compaction.
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Mechanical Strength of aggregates
Gradation
Properties of the Soil
Presence of Salts
Compaction
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Mechanical Strength
When the soil is used in small proportion to fill
up the voids the crushing strength of aggregates
is important
Gradation
A well graded aggregate soil mix results in a mix
with high dry density and stability values
Properties of soil
A mix with Plasticity Index, results poor stability
under soaking conditions. Hence it is desirable tolimit the plasticity index of the soil
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Presence of Chemicals
Presence of Salts like Sulphates and mica
are undesirable
Presence of Calcium Chloride is BeneficialCompaction
Effective Compaction is desirable to
produce high density and stability mix
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Soil Cement is an intimate mix of soil, cement
and water, compacted to form a strong base
course
Cement treated or cement modified soil refers to
the compacted mix when cement is used in
small proportions to impart some strength
Soil Cement can be used as a sub-base or base
course for all types of Pavements
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Soil
Cement
Pulverisation and Mixing
Compaction
Curing Additives
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Soil
THE PHYSICAL PROPERTIES
Particle Size Distribution
Clay content
Specific Surface
Liquid limit and Plasticity Index
Cement
A increase in cement content generally causes
increase in strength anddurability
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Pulverisation and Mixing
Better the Pulverisation and degree of mixing,
higher is the strength
Presence of un pulverised dry lumps reduces
the strength
Compaction
By increasing the amount of compaction dry
density of the mix, strength and durabilityalso increases
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Curing
Adequate Moisture content is to be retained in
order to accelerate the strengthAdditives
There are some additives to improve properties
Lime
Sodium hydroxide
Sodium Carbonate Calcium Chloride
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Soil Cement specimens are prepared with
various cement contents in constant volumes
moulds
The compressive strength of these specimens
tested after 7 days of curing
A graph is plotted Cement content Vs
compressive strength
The Cement Content Corresponding to a
strength of 17.5 kg/cm2 is taken as design
cement content
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Soil- Lime has been widely used as a
modifier or a binder
Soil-Limeis used as modifier in high plasticity
soils
Soil Lime also imparts some binding action
even in granular soils
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Soil-Lime is effectively used in Expansive
soils with high plasticity index.
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Lime Content
Generally increase in lime content causes
slight change in liquid limit and considerable
increase in Plasticity index
The rate of increase is first rapid and then
decreases beyond a certain limit
The point is often termed as lime fixationpoint
This is considered as design lime content
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Type of Lime
After long curing periods all types of limes produce
same effects. However quick lime has been foundmore effective than hydrated lime
Calcium Carbonate must be heated at highertemperature to form Quick lime calcium oxide( CaO)
Calcium oxide must be slaked ( by the addition ofwater) to form Hydrated lime
Compaction Compaction is done at OMC and maximum dry
density.
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Curing
The strength of soil-lime increases with curing
period upto several years. The rate of
increase is rapid during initial period
The humidity of the surroundings also affects
the strength
Additives
Sodium metasilicate, Sodium hydroxide and
Sodium Sulphate are also found useful
additives
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The Basic Principles of this stabilization are
Water Proofing and Binding
By Water Proofing inherent strength and
other properties could be retained
Most Commonly used materials are Cutback
and Emulsion
Bitumen Stabilized layer may be used as
Sub-base or base course for all the roads
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Soil
The particle size, shape and gradation of the
soil influence the properties of the soil-bitume
mix.Types of Bitumen
Cutbacks of higher grade should be preferred
Emulsions generally gives slightly inferiorresults than Cutback.
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Amount of Mixing
Increasing proportion of bitumen causes a
decrease in dry density but increases the
stability after a certain bitumen content
The optimum bitumen content for maximum
stability generally ranges from 4 to 6%Mixing
Improved type of mixing with low mixing period
may be preferred
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Compaction
Effective Compaction results higher
stability and resistance to absorb waterAdditives
Anti stripping and reactive chemical additives have been tried to improve
the properties of the mixes
Portland cement can also be used along with the soil bitumen
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Scarcity of good quality aggregates / soil for
road construction
Production and accumulation of different
waste materials
Disposal and environmental problem
Economical and gainful utilisation
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Quality of waste is not controlled by theirmanufacturers
Characteristics of by-products vary in a widerange
Road construction practice is accustomed totraditional materials of steady quality
Specifications of layers compaction of traditionalmaterials are not suitable for waste materials
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Amount of yearly produced waste materialshould reach a certain lower limit
The hauling distance should be acceptable
The material should not have a poissonous effect The material should be insoluble in water
The utilisation should not have a pollutionaleffect to the environment
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Free from organic matter
Should not swell or decay as influenced by water
Should not be soluble in water
Particles should be moderately porous
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Thermal Power Stations* Fly ash
* Bottom ash
* Pond ash
Steel Plants* Blast furnace slag
* Granulated blast furnace slag
* Steel slag
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Thermal power - Major role in powergeneration
Indian scenario - Use of coal with highash content
- Negligible utilisationof ash produced
Bulk utilisation - Civil engineeringapplications like
construction of roads &embankments
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n Can be used for construction ofn Embankments and backfillsn Stabilisation of subgrade and sub-base
n Rigid and semi-rigid pavements
n Fly ash properties vary widely, to be characterised
before use
n Major constituents - oxides of silica, aluminum,iron, calcium & magnesium
n Environmentally safe material for roadconstruction
n Possesses many favourable properties forembankment & road construction
Utilisation of fly ash
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Parameter Range
Specific Gravity 1.90 2.55
Plasticity Non plastic
Maximum dry density (gm/cc) 0.9 1.6
Optimum moisture content (%) 38.0 18.0
Cohesion (kN/m2) Negligible
Angle of internal friction (j) 300 400
Coefficient of consolidation Cv (cm2/sec) 1.75 x 10
-52.01 x10-3
Compression index Cc 0.05 0.4
Permeability (cm/sec) 8 x 10-67 x 10-4
Particle size distribution (% of materials)Clay size fraction
Silt size fraction
Sand size fraction
Gravel size fraction
1 10
8 85
7 90
0 10
Coefficient of uniformity 3.1 10.7
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Ideally suited as backfill material for urban/ industrial areas andareas with weak sub soils
Higher shear strength leads to greater stability
Design is similar to earth embankments
Intermediate soil layers for ease of construction and to provideconfinement
Side slope erosion needs to be controlled by providing soil cover
Can be compacted under inclement weather conditions
15 to 20 per cent savings in construction cost depending on leaddistance
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Earth
CoverEarth
Cover
Bottom ash or
Pond ash
Typical cross section of fly ash road embankment
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Approach embankment for second Nizamuddinbridge at Delhi
Length of embankment - 1.8 km
Height varies from 6 to 9 m
Ash utilised - 1,50,000 cubic metre
Embankment opened to traffic in 1998
Instrumentation installed in the embankment
showed very good performance
Approximate savings due to usage of fly ash is
about Rs.1.00 Crore
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Approach embankment for second Nizamuddinbridge at Delhi
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Spreading of pond ash
Compaction of pond ash
Second Nizamuddin bridge approach embankment
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Stone pitching for slope
protection
Traffic plying on the
embankment
Second Nizamuddin bridge approach embankment
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Water logged area
(soft ground conditions)
Compaction of fly ash over layer of geotextile
Length of stretch
54 km
Height of embankment 3 to
4 m
Fly ash utilisation 2 Million
cubic metres
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Fly ash - better backfill material for reinforcedembankments
Polymeric reinforcing materials Geogrids,
friction ties, geotextiles Construction sequence similar to reinforced
earth structures
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Pond AshFill
7.8 to
5.9 m
Facing
panels
Filter
medium Geogrids
Reinforced foundation mattress of bottom ash
Okhla flyover approach embankment
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Okhla flyover approach embankment
Erection of facing panels
Rolling of pond ash
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Support provided to facing
panels during construction
Laying of geogrids
Okhla flyover approach embankment
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Geogrid reinforced fly ash approach embankment
Length of embankment
138.4 m Height varied from 3.42 m to 1.0 m
Opened to traffic in 1997
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Sarita Vihar flyover reinforced approach embankment
Arrangement of frictionties before laying pond ash
Laying of friction ties
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Compaction using platevibrator near the facing
panels
Compaction of pond ash
using static and vibratory
rollers
Sarita Vihar flyover reinforced approach embankment
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Stabilised soil subgrade & sub-base/base courses
Mixing with soil reduces plasticity characteristics ofsubgrade
Addition of small percentage of lime or cement greatlyimproves strength
Leaching of lime is inhibited and durability improves due to
addition of fly ash Pond ash & bottom ash can also be stabilised
Lime-fly ash mixture is better alternative to moorum forconstruction of WBM / WMM
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Construction of semi-rigid/ rigid pavements
Lime-fly ash concrete
Dry lean cement fly ash concrete
Roller compacted concrete
Fly ash admixed concrete pavements
Lime-fly ash bound macadam
Precast block paving
High performance concrete
Fly ash for road construction
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WBM Gr II/WMM 150 mm
WBM Gr III/WMM 75 mm
GSB 350 mm
BM 75 mm
DBM 100 mm
Bituminous concrete 40 mm
Typical cross section of flexible pavement conventionalsection
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Fly ash + 6% cement stabilised layer
150 mm
Typical cross section of flexible pavementusing fly ash
WBM Gr III/WMM 75 mm
Pond ash 350 mm
BM 75 mm
DBM 100 mm
Bituminous concrete 40 mm
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Pond ash 300 mm
DLFC 100 mm
Fly ash admixed PQC 300 mm
Typical cross section of rigid pavement using fly ash
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Mixing of lime stabilised
pond ash
Compaction of stabilised
pond ash using road roller
Demonstration road project using fly ash at Raichur
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Construction of roller
compacted concretepavement
View of the demonstrationroad stretch after three years
Demonstration road project using fly ash at Raichur
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Bottom ash
RCCP wearing course - 0.1 m
Stabilised fly ash
base - 0.1 mStabilised fly ash
Shoulder
Soil cover
Demonstration road project using fly ash near Dadri
(U.P) Typical section
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Stabilised base course
Compaction of RCCPMixing & laying of RCCP
Demonstration road
project using fly ash
near Dadri (U.P)
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Guidelines available on pavement construction
IRC 60Tentative guidelines for use of lime fly ash concrete
as pavement base or sub-base
IRC 68 Tentative guidelines on cement fly ash concrete for
rigid pavement construction
IRC 74 Tentative guidelines for lean cement concrete andlean cement fly ash concrete as a pavement base or sub-
base
IRC 88 Recommended practice for lime fly ash stabilised soil
as base or sub-base in pavement construction
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Published recently by Indian Roads Congress (SP-58:2001)
Includes design aspects also
Handling and construction
Loose layer thickness of 400 mm can be adopted ifvibratory rollers are used
Moisture content - OMC + 2 per cent
Use of vibratory rollers advocated
Minimum dry density to be achieved - 95 per cent ofmodified Proctor density
Ash layer and side soil cover to be constructedsimultaneously
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Total production of slag from steel industries isabout 8.0 million tonnes
Types of slags
Blast furnace slag Granulated blast furnace slag (GBFS)
Air cooled slag
Steel slag
Granulated blast furnace slag
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g
Contains reactive silica
Suitable for lime / cement
stabilisation
Air cooled blast furnace slag
Non
reactiveSuitable for use as
coarse aggregates
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Characterization of slags produced at different steel
plants
Laboratory studies on Lime-GBFS mixes
Semi-field studies on Lime-GBFS concrete
Test track studies on usage of slags in road works
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Property Durgapur Bhilai Rourkela DelhiQuartzite
Specificationrequirements
Specific
gravity
2.78
2.82
2.82
3.33
2.97
2.99
2.67 -
Waterabsorption(%)
1.53 1.72
0.58 1.38
0.74 1.29
0.48 2% Max
Los
Angelesabrasionvalue (%)
18.80 25.00 14.28 34.00 40% Max
Impactvalue (%)
15.79 14.80 16.90 24.50 30% Max
Soundnessvalue (%) 1.66 1.17 0.33 0.17 12% Max
Percentagevoids
46.40 43.90 43.10 43.80 -
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Obtained as a waste product during productionof steel
Particle size varies from 80 mm to 300 microns
Compared to blast furnace slag, steel slagcontains lower amount of silica, higheramounts of iron oxide and calcium oxide
Due to presence of free lime, steel slag should
be weathered before using it in construction
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Plant roads at Visakhapatnam
Test tracks in collaboration with AP PWD using slags
from Visakhapatnam Steel Plant
Test tracks in collaboration with Orissa PWD usingslags from Rourkella Plant
Test tracks at R&D Centre for Iron & Steel, Ranchi
using Slags from Bokaro Plant
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Construction of
test track using
slag at Orissa
Labour based techniques for
construction of stabilised
layer
Li
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View of finishedsurface of road
constructed using
slags at Orissa
Lime
stabilisation of
iron slags
(Orissa)
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Processed municipal wastes
utilised for construction of test
track on village road near Delhi Stabilised municipal waste used
for construction of sub-base layer
Performance of stretch is good