GROUND IMPROVEMENT
Syllabus
• WHAT ?
• Need?
• How ?
NEED FOR ENGINEERED GROUND IMPROVEMENT
CONCERNS
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Mechanical properties are not adequate
Swelling and shrinkage
Collapsible soils
Soft soils
Organic soils and peaty soils
Sands and gravelly deposits
Foundations on dumps and sanitary landfills
Handling dredged materials
Handling hazardous materials in contact with soil
Use of old mine pits
Courtesy :NPTEL
Courtesy :NPTEL
Our blunder became a world
wonder
• Most well known
architectural oddity
• Construction began in the
12th century and was
completed in the 14th
century
• The height of the tower is
55.86 metres
• Noticed the tilt during
construction itself
• in 1990 the tilt was 5o
Reasons
1. Inadequate
foundation
2. Resting on very
soft silty soil
3. Fluctuating
water table
which would
perch higher on
one side of the
tower
Stabilisation
efforts
Sealed the base with
cement grout
In 1992 first storey was
braced with steel tendons
In 1993 600 tonnes of lead
ingots were stacked
around the base of the
higher side
In 1995 anchors were
installed 40m deep
1999-2001 soil was
removed from the higher
side
In 2003 a new drainage
system was introduced
Strategies
When a project encounters difficult foundation conditions, possible
alternative solutions are..
• Avoid the particular site.
• Design the planned structure(flexible/rigid) accordingly.
• Remove and replace unsuitable soil.
• Attempt to modify existing ground.
GROUND IMPROVEMENT TECHNIQUE
Soil/Ground improvement in geotechnical engineering means
techniques that
• increase soil shear strength,
• reduce soil compressibility ,
• reduce soil permeability.
Classification of Ground Improvement
• Mechanical Modification
• Hydraulic Modification
• Physical and Chemical Modification
• Thermal methods of ground improvement
• Modification by inclusion & Confinement
• Combination of above
Mechanical Modification
• Increasing density of
soil by the application
of short term
mechanical forces
– Compcation of surface
layers by static vibratory
or impact rollers or plate
vibrators
– Deep compcation by
heavy tamping at surface
or vibration at depth
Hydraulic Modification
• Free pore water is
forced out via drains or
wells
– Lowering or ground
water by pumping from
bore holes or trenches
for coarse grained soil
– preloading or electro
kinetic stabilisation for
fine grained soil
Physical and Chemical Modification
• Physically mixing
additives
– Natural soil
– Industrial byproducts or
waste materials
– Cementitious materials
additives injected via
boreholes under
pressure is termed as
grouting
Thermal methods of ground
improvement
• Heating and Freezing
• Heating evaporates
water and causes
permanent changes in
mineral structure of
soils
• Freezing solidifies water
and bonds individual
particles together
Modification by inclusion &
Confinement
• Reinforcements impart
tensile strength to soil
mass
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Fibres
Strips
Bars
Meshes
• In-situ reinforcement is
achieved by means of
nails and anchors
GI FOR DIFFERENT SOIL TYPE
RED COLOUR
Technique which is not applicable
Courtesy :NPTEL
Factors affecting the choice of a
particular method
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Type & degree of improvement required
Type of soil, geological structure, seepage condition.
Cost ,equipments & spec.
Construction time
Possible damage to adjacent building or pollution for Ground water
resources
Durability of the materials involved
Toxicity & corrosivity of any chemical additives
Reversibility & irreversibility of the process
Reusability of components such as steel, plastics..
Reliability of testing, analysis & design
Good method of testing
Feasibility of construction control & performance measurement.
Document of quality control & performance
Objectives
• Increase in strength
• Reduce distortion under stress
• Reduce compressibility
• Prevent physical or chemical changes due to environmental
condition.
• Reduce susceptibility to liquefaction
• Reduce natural variation of borrow material &foundation soils.
Soil Distribution in India
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Marine deposits
Black Cotton soils
Laterites, lateritic soils and Murrums
Alluvial deposits
Dessert soils
Boulder deposits
Marine deposits
• Very soft to soft , normally consolidated
highly compressible clays
• Slight to medium sensitive
• Essentially inorganic
• Thickness vary from 5 to 20m
• Need pre-treatment before application
of external load
Found along the coasts
of
West Bengal
Andhra Pradesh
Tamil Nadu
Kerala
Pondicherry
Karnataka
Maharashtra
Gujarat
Black Cotton Soil
• One of the major soil deposits of India,
spread over 300000 sq km
• Found in regions having low to medium
slope and poor drainage conditions
• Primary bed rock is basalt or trap
• Expansive in nature due to the presence of
montmorillonite mineral
• Depth of deposit can be as high as 20m
• Volume changes upto 1.5m due to seasonal
moisture changes
• Since susceptible to swelling and shrinkage
special treatment or design approach has
to be adopted
Extends over
Maharashtra
Madhya Pradesh
Karnataka
Andhra Pradesh
Tamil Nadu
Uttar Pradesh
Laterites, lateritic soils and Murrums
• Red pink or brown coloured residual
deposits
• Halloysite clay mineral is present
• Coarse grained concretionary material with
90% of lateritic constituents is called laterite
• Fine grained material with low
concentration of oxides is called lateritic soil
• Covers an area of 100000 sq km
• High strength when it is cut and dried in sun
• Porous in nature
• Medium to high permeability
• Murrums are residual soils formed from
weathering of basaltic rock where monsoon
is severe
• Consists of mixture of weathered rock
pieces clayey sand and clay
Extends over
Kerala
Karnataka
Maharashtra
Orissa
West Bengal
Alluvial Deposits
• Consist of alternate layers of sand
silt and clay and in some locations
organic layers are also there
• In some regions thickness even
exceed 100m
Found in
Indo-gangetic and
Brahmaputra flood plains
Bengal basin
Assam in east to Punjab in
the west
Dessert Soils
• Wind blown deposits in the form of
sand dunes with an average depth of
15m
• Formed under arid conditions
• Dunes are non plastic uniformly
graded fine or silty sand
• Covers about 500000 sq km
Found in Rajasthan
Boulder Deposits
• Carried down hills due to rivers
and deposited at foot of hills
• Found in sub Himalayan regions
• Complex properties depending on
the size of the boulders and the
soil matrix
• High frictional resistance due to
particle contact
Reclaimed Soils
• All materials dumped on a site where a structure
is to be constructed are called reclaimed soils
usually done on low lying unusable areas or
water bodies
due to shortage of land forced to plan
construction on reclaimed land
excessive settlement, slope staibility and poor
bearing capacity
reclamation is usually followed with ground
improvement
Classification of Reclamation materials
• Hydraulic fills or dredged soil
• Sanitary fill
• Paper sludge
• Fly ash including slag
• Rubbish and debris
Hydraulic fills or dredged soil
• Used for large reclamation
• Soil required will be
obtained from adjacent
river, lake or ocean
• Sand deposits need to be
densified before
construction
• If it is silt or clay it will be
left to consolidate and
stabilize natuarally
• Quick dumping of well
graded material was found
to produce good results
upto a depth of 15m
Sanitary fill
• Waste disposal sites
• Leachate can pollute drinking
water and cause bad odours
• Periodic collection and treatment
of leachate is required
• Methane or other gases formed
can lead to explosion or fire
hazards
• Large settlement due to
 movement of fine
material
into large voids
 material loss due to chemical
and biological reactions
 Creep
 consolidation
Paper sludge
• Used as a material for
landfilling
• Consist of kaolinite and
organic cellulose fibres
with an ash content of 32
to 59%
• Density is low
• Shear strength increases
as consolidation proceed
and attains good bearing
capacity with time
Fly ash including slag
• More stable material
• Steel furnace slag is
used but blast furnace
slag not used
• Incineration residues
are also used
• Materials are light
weight and highly
alkaline
Rubbish and debris
• Most heterogeneous
material ranging from
stone, concrete pieces
to paper, glass, grass etc
• Used as bottom portion
of the fill and is rolled
• Highly compressible
and load test has to be
done to evaluate the
strength and settlement
characteristics
Ground Improvement Potential
• Ground condition-not same everywhere
• Based on condition
– Hazardous
– Poor
– Favourable
Hazardous
• A regular design approach or economical
treatment technique not feasible
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Near faults in seismically active regions
Loose to medium dense fine sands
Location underlain by dormant or active mines
natural slopes in glacial or lacustrine clay, clay shales,
colluvium, thick deposits of residual soils
– Flood plains
– Landfill or hazardous waste dumps
As far as possible such land should be avoided
Poor
• Loess, porous lightly
cemented clays, low
density recent alluvium of
arid climate valleys
– Collapse on saturation
resulting in subsidence
– Saturation may be
prevented or pre colapse
the soil by flooding
– Structure designed with
large allowable sttlement
• Expansive soil like black
cotton soil
– Large change in volume
with change in water
content
– Active zone need to be
identified and structure
should be designed
accordingly
– Depth of active zone is less
a suitable ground
improvement technique
has to be used
Poor
• Soft to firm clays
– Low bearing capacity
– Highly sensitive to
disturbance
– Some are highly fissured
– Undergo long term
consolidation of significant
magnitude
– Design of suitable deep
foundation or ground
improvement technique
• Organic Soils
– Highly compressible
– If depth is less suitable
ground improvement
technique is feasible
– Removal and replacement
Loose sand and silt proper
treatment is required
Favourable
• Cohesive granular soils and sand clay mixtures
– Strong and form good supporting medium for
moderately to heavily loaded structure
• Cohesionless granular soil such as medium
dense to dense sand
– for most loading conditions
• Shallow rock without discontinuities
– Any type of loading