INDEX:

1. ABSTRACT

2. INTRODUCTION

3. GROUND IMPROVEMENT TECHNICS

3.1REMOVAL AND REPLACEMENT OF SOIL

3.2 PRECOMPRESSION OF SOIL

3.3DENSIFICATION TECHNQUES

3.3.1 VIBRO TECHNICS

3.3.1.1 VIBRO COMPACTION

3.3.1.2 VIBROFLOTATION

3.3.2 DYNAMIC COMPACTION

3.3.3 BLASTING

3.3.4 COMPACTION GROUTING

3.4 REINFORCEMENT TECHNIQUES

3.4.1 STONE COLUMNS

3.4.2 COMPACTION PILES

3.4.3 DRILLED INCLUSIONS

3.5 GROUTING TECHNIQUES

3.5.1 PERMEATION GROUTING

3.5.2. JET GROUTING

3.6 STABILIZATION USING ADMIXTURES

3.6.1 MECHANICAL STABILIZATION

3.6.2 CHEMICAL STABILIZATION

3.6.2.1 CEMENT STABILIZATION

3.6.2.2 LIME STABILIZATION

3.6.2.3 FLY ASH STABILIZATION

3.7 GEO TEXTILES

3.8 ELECTROOSMASIS METHOD

4. CONCLUSION

5.BIBILOGRAPHY

1. ABSTACT:

Ground improvement is the

most imaginative field of geotechnical

engineering. It is a field in which the

engineer forces the ground to adopt the

project's requirements, by altering the

natural state of the soil, instead of having to

alter the design in response to the ground's

natural limitations. The results usually

include saving in construction cost and

reduction of implementation time.

There are number of techniques

available for improving the mechanical and

engineering properties of the soil. However,

each technique has some limitations and suit

abilities to get maximum improvement in

the soil conditions with minimum effort.

Some of the important techniques are

discussed in this paper.

To improve the strength of the

soils, especially in case of granular type of

soils, COMPACTION METHODES are

found as best methods among all type of

techniques. Based on the mechanism applied

for compacting the soil, it is sub divided into

different methods like dynamic compaction,

blasting, vibro techniques ...etc.These

are briefly discussed in this paper.

When there are some

limitations encountered for applying the

above technique, grouting techniques,

stabilization of soil using different

admixtures can be adopted effectively

which can bring variations in the soil

conditions. The various types of above

techniques are briefly discussed in this

paper.

Finally, recent advancements

in ground improving techniques using

GEOTEXTILES, ELECTRIC

TREATMENT METHODES are also

briefly discussed in this paper. These

techniques are widely used in these days.

2. INTRODUCTION:

Large civil engineering

projects are being executed in all over

the country in order to enhance the

infrastructure of the country.

Infrastructure facilities have to be often

built at sites where the soil conditions

are not ideal. The insitu soil

characteristics of a construction site are

different from those desired, and almost

always far from ideal for a designed

need. With increased urban

development, site with favorable

foundation conditions became depleted.

At times the civil engineer has been

forced to construct structures at site

selected for reasons other than soil

conditions. Thus it is increasingly

important for the engineer to know the

degree to which soil properties may be

improved or other alterations that can be

thought of for construction of an

intended structure at stipulated site.

If unsuitable soil conditions are

encountered at the site of a proposed

structure, one of the following four

procedures may be adopted to insure

satisfactory performance of the structure.

By pass the unsuitable soil by

means of deep foundations

extending to a suitable bearing

material.

Redesign the structure and it's

foundation for support by the poor

soil. This procedure may not be

feasible or economical.

Remove the poor material and either

treat it to improve and replace it (or)

substitute for it with a suitable

material.

Treat the soil in place to improve its

properties.

Rigid foundations such as piling

present a solution but these are often

expensive. In such circumstances,

ground improvement using different

techniques offers a proved and economic

solution. At present a variety of soil

improvement techniques are available

for making soil to bear any type of

structure on it and also for mitigation of

seismic hazards. The costs of these

methods vary widely and the conditions

under which they can be used are

influenced by nature and proximity of

structures and construction facilities.

3. GROUND IMPROVEMENT TECHNIQUES:

On the basis of mechanism by

which they improve the engineering

properties of soil, the most of common

of these can be divided into the

following major categories. These are

Densification techniques.

Reinforcement techniques.

Stabilization techniques.

Miscellaneous methods

Apart from the methods listed

above, there are some other simple

methods like removal and replacement

of soil. In this paper these are discussed

first before taking up above techniques.

3.1. REMOVAL AND REPLACEMENT OF SOIL:

One of the oldest and simplest

soil improvement methods is to simply

excavate the unsuitable soil and replace

them with compacted fill. This method

is often used when the problem the soil

is that it is too loose. In that case, the

same soils used to build the fill, except

now it has a higher unit weight (because

of compaction) and thus has been better

engineering properties. This is a

common way to remediate problems

with collapsible soils.

Removal also may be available

option when the excavated soils have other

problems, such as contamination or

excessive organics, and need to hauled

away. This method can be expensive

because of the hauling costs and the need for

imported soils to replace those that were

excavated. It also can be difficult to find a

suitable disposal site for the excavated soils.

Removal and replacement is

generally practical only above the

ground water table. Earthwork

operations become more difficult when

the soil is very wet, even when the free

water pumped out, and thus are

generally avoided unless absolutely

necessary.

3.2. PRECOMPRESSION OF SOIL:

Another old and simple method

of improving soils is to cover them with

a temporary surcharge fill as shown in

figure. This method is called

precompression, preloading, or

surcharging. It is especially useful in

soft clayey and silty soils because the

static weight of the fill causes them to

consolidate, thus improving both

settlement and strength properties. Once

the desired properties have been

obtained, the surcharge is removed and

construction proceeds on improved site.

Pre-compression has the following

advantages

It requires only conventional

equipment earthmoving equipment,

which is readily available. No

special or proprietary equipment is

needed.

Any grading contractor can perform

the work.

The results can be effectively

monitored by using appropriate

instrumentation and ground level

surveys.

The method has a long track record

of success.

The cost is comparatively low, so

long as soil for preloading is readily

available.

However, there also are

disadvantages

The surcharge fill generally must

extend horizontally at least 10m

beyond the perimeter of the planned

construction. This may not possible

for confined sites.

The transport of large quantities of

soil onto the sites may not be

practical, or may have unacceptable

environmental impacts (i.e., dust,

noise, traffic) on the adjacent areas.

The surcharge must remain in place

for months or years, thus delay in

construction.

3.3 DENSIFICATION TECHNIQUES:

The strength and

stiffness of the soil is higher when the

particles are packed in a dense

configuration than they are packed

loosely. As a result, densification is one

of the most effective and commonly

used means of improving soil

characteristics. This can be approaches

in following ways.

3.3.1 VIBRO TECHNIQUES:

Vibro techniques use probes that

are vibrated through soil deposit in a

grid pattern to densify the soil over the

entire area of thickness of the deposit.

These are classified in to the following

methods. These are

3.3.1.1VIBRO COMPACTION:

Vibro compaction is a method

for compacting deep granular soils by

repeatedly inserting a vibratory probe. It

is also known as VIBRO

DENSIFICATION.

By inserting depth vibrators, the

vibrations are produced by rotating a

heavy eccentric weight with the help of

an electrical motor with in the vibrator.

The vibratory energy is used to

rearrange the granular particles in a

denser state. Penetration of the vibro

probe is typically aided by water jetting

at the tip of the probe.

The Vibro-Compaction Process

Some of advantages and disadvantages of

this method are given below.

It is often an economical alternative

to deep foundations, especially

when considering the added

liquefaction protection in seismic

areas.

It is most effective in granular soils

It cannot be used in cohesive soils

3.3.1.2. VIBRO FLOTATION:

In vibro flotation a torpedo like

probe (the vibro float) suspended by a

crane is used to density a soil

deposit.Vibro floats usually 12 to 18

inch in diameter and about10 to 16 ft

long, contain weights mounted

eccentrically on a central shaft driven by

electric or hydraulic power.

The vibro float is initially

lowered to the bottom of the deposit by a

combination of vibration and water or

air jetting through ports in its pointed

nose cone. The vibro float is then

incrementally with drawn in 2 to 3 ft

intervals at an over all rate of about 1ft /

min while still vibrating. Water may be

jetted through ports in the upper part of

the vibro float to loosen the soil above

the vibro float temporarily and aid in its

with drawl. The vibrations produce a

localized zone of temporary liquefaction

that causes the soil surrounding the vibro

float to densify.

Principle of the technique

Vibro flotation is most

effective in clear granular soils

with the fine contents less than

20% and clay contents below

3%.

Vibro flotation has been used

successfully to density soils to

deep [this of up to 115 ft.]

3.3.2. DYNAMIC COMPACTION:

Dynamic compaction is a ground

improvement process for compacting

and strengthening loose or soft soils to

support buildings, roadways, and other

heavy construction. The method

involves the systematic dropping of

heavy weights, 100 to 400kN, from a

height of 5 to 30m, in a pattern designed

to remedy poor soil conditions at the

proposed building site. In soft ground

areas, dynamic compaction has proved

to be an effective and economical

alternative to preloading, foundation

piling, deep vibratory compaction, and

soil undercutting and replacement

Dynamic Compaction is normally used

under the following circumstances:

To increase in-situ density and in

this way improve the bearing

capacity and consolidation

characteristics of soils (or waste

materials) to allow conventional

foundation and surface bed

construction to be carried out. The

technique typically improves the in-

situ soils such that allowable

bearing pressures of up to 250 Kpa

can be used with foundation

settlements of the order of 10 to 20

mm.

To increase in-situ density and in

this way improve in-situ

permeability and/or reduce

liquefaction potential

What soils are suitable?

Most soil types can be

improved, including silts and some

clays. The most commonly treated soils

are old fills and granular virgin soils.

Soils below the water table are routinely

treated. However, careful control has to

be used to allow dissipation of excess

pore pressures created during the weight

dropping.

3.3. 3. BLASTING:

Blasting densification

involves the detonation of multiple

explosive charges vertically spaced at 10

to 20 ft apart in drilled or jetted bore

holes. The bore holes are usually spaced

between 15 to 50 ft apart and back filled

prior to detonation. The efficiency of

densification process can be increased

by detonating the charges at different

elevations at small time delays.

Immediately after detonation, the ground

surface rises & gas & water are expelled

from fractures. The ground surface then

settles as the excess gas & water

pressure dissipates. Two or three rounds

of blasting are often used to achieve the

desired degree of densification.

Blasting is most effective in

loose sands that contain less than

20% silt and less than 5% clay.

Although blasting is quite

economical, it is limited by

several considerations, as it

produces strong vibrations that

may damage near by structures

or produce significant ground

movements.

3.3.4. COMPACTION

GROUTOING:

Compaction grouting

uses displacement to improve ground

conditions. A very viscous (low

mobility) aggregate is pumped in stages,

forming grout bulbs, which displace and

densify the surrounding soils.

A consistency soil

cement paste is injected under pressure

in to the soil mass, consolidating, and

there by densifying surrounding soils in

place. The injected ground mass

occupies void space created by pressure-

densification. Pump pressure transmitted

through low mobility grout, produces

compaction by displacing soil at depth

until resisted by the weight of over lying

soils.

Fine grained soils with sufficient

permeability to allow excess

water to dissipate best suits for

compaction grouting.

It has also been used successfully

in a wide variety of soils and

fills.

3.4. REINFORCEMENT

TECHNIQUES:

In some cases it is possible to

improve the strength and stiffness of a

existing soil deposit by installing

discrete inclusions that reinforce the soil.

These inclusions may consist of

structural materials, such as steel,

concrete or timber and geomaterials

such as densified gravel.

3.4.1. STONE COLUMNS:

Soils deposits can be improved

by the installation of dense columns of

gravel known as stone columns. They

may be used in both fine and coarse

grained soils. In fine-grained soils, stone

columns are used to increase the shear

strength beneath structures and

embankments by accelerating

consolidation (by allowing radial

drainage) and introducing columns of

stronger material.

Stone columns can be installed in

a variety of ways. (They may be

constructed by introducing gravel during

the process of vibroflotation) In the

Frankie method, a steel casing initially

closed at the bottom by a gravel plug is

driven to the desired depth by an internal

hammer. At that depth part of the plug is

driven beyond the bottom of the casing

to form a bulb of gravel. Additional

gravel is then added and compacted as

the casing is with drawn. The diameter

of the resulting stone column depends on

the stiffness and compressibility of the

surrounded soil

3.4.2. COMPACTION PILES:

Granular soils can be improved

by the installation of compaction piles.

Compaction piles are displacement

piles , usually prestressed concrete or

timber, that are driven into a loose sand

or gravel deposit in a grid pattern and

left there.

Compaction piles improve the

seismic performance of a soil by three

different mechanisms. First the flexural

strength of piles themselves provides

resistance to soil movement

(reinforcement). Second, the vibrations

and displacements produced by their

installation cause densification. Finally,

the installation process increases the

lateral stress in the soil surrounding the

piles.

Compaction piles generally

densify the soil with in a distance of 7 to

12 pile diameters and consequently are

usually installed in a grid pattern.

Between compaction piles a relative

density of up to 75% to 80% are usually

achieved. Improvement can be obtained

with reasonable economy to depth of

about 60ft.

3.4.3 DRILLED INCLUSIONS:

Structural reinforcing elements

can also be installed in the ground by

drilling or auguring. Drilled shafts, some

times with very large diameters, have

been used to stabilize many slopes.

Soil nails, tie backs, micro piles

have been used for this purpose. The

installation of such drilled inclusions can

be quite difficult. However in the loose

granular soils that contribute to increase

the strength of the soil in a every

effective manner.

3.5 GROUTING AND MIXING

TECHNIQUES:

Grouting techniques involve of

cementitious materials into voids of the

soil or into fractures in the soil so that

the particle structure of the majority of

the soil remains intact.

Mixing techniques introduce

cementitious materials by physically

mixing them with the soil, completely

disturbing the particle structure of the

soil. Grouting and mixing techniques

tend to be expensive but can often be

accomplished with minimal settlement

or vibration.

3.5.1.PERMEATION GROUTING:

Permeation grouting involves the

injection of low viscosity liquid grout

into the voids of the soil without

disturbing the soil structure. Particulate

grouts (i.e., aqueous suspensions of

cement, fly ash, bentonite, micro fine

cement or some combination there of) or

chemical grouts (e.g., silica & lignin

gels, or phenolic & acrylic resins) may

be used.

Grout pipes are typically

installed in a grid pattern at spacing of 4

to 8 feet. The grout may be injected in

different ways. In ‘stage grouting’, a

boring is advanced a short distance

before grout is injected through the end

of the drill rod. After the grout sets up,

the boring is advanced another short

distance and grouted again. This process

continues until grout has been placed to

the desired depth.

Permeation grouting produces

soil improvement by two mechanisms.

First the grout tends to strengthen the

contacts between individual soil grains,

there by producing a soil skeleton that is

stronger and stiffer than that of the un

grouted soil. Second, the grout takes up

space in the voids between soil particles,

reducing the tendency for densification.

Stopping leaks in below-

grade structures

Stopping leaks in below-

grade utilities

Excavating support of non-

corrosive soils

Strengthening of soil mass

to accept new loads

3.5.2. JET GROUTING:

:

In Jet grouting the soil is mixed

with cement grout injected horizontally

under high pressure in a previously

drilled bore hole.

Jet grouting uses a special pipe

equipped with horizontal jets that inject

grout into the soil at high pressure. The

pipes are first inserted to the desired

depth, then they are raised and rotated

while the injection is in progress, thus

forming a column of treated soil.

Because of high pressure, this

method is usable on a wide range of

soil types.

3.6. STABILIZATON USING

ADMIXTURES:

SOIL STABILIZATION: It is the process

of improving the engineering properties of

soil by mixing some binding agents thus

binding the soil particles .In a broader sense

it also includes compaction, pre

consolidation and many more such process.

Soil stabilization is classified as

Mechanical

stabilization

Chemical

stabilization

3.6.1.MECHANICAL STABILIZATION:

Mechanical stabilization is the process of

improving the properties of soil by changing

its gradation. Two (or) more types of natural

soils mixed to obtain composite which is

suspension to any of its components

3.6.2. CHEMICAL STABILIZATION:

Chemical stabilization is the form of lime,

cement, fly ash and the combination of the

above is widely used in soil stabilization to

Reduce the

permeability of the soil.

Improve shear

strength.

Increase bearing

strength.

Decrease

settlement.

Soil and chemicals are mixed either

mechanically in place or by bath

process .the optimum benefit of using these

agents in stabilization must be determined

by laboratory testing. The general principle

of these admixtures as stabilizers are

discussed below.

3.6.2.1. LIME STABILIZATION: This is

done by adding lime to soil. It is useful for

stabilization of clayed soils. When lime

reacts with soil, there is exchange of cations

in the adsorbed water layer and a decrease in

plasticity of soil occurs .The resulting

material is more friable than the original

clay and is therefore more suitable as sub

grade.

This method is not effective for

sandy soils. However these soils can be

stabilized in combination with clay, fly

ash or other pozzolanic materials, which

serve hydraulically reactive in gradients.

3.6.2.2. CEMENT STABILIZATION:

Cement stabilization is done by mixing

pulverized soil and Portland cement with

water and compacting the mix to attain a

strong material .The material obtain by

mixing soil and cement is known as soil

cement .The mix becomes hard and durable

structural material as the cement hydrates

and develops strength.

The soil cement is quite weather

resistant and strong. It is commonly used

for stabilizing sandy and other low

plasticity soils. Cement interacts with

the silt and clay fractions and reduced

their affinity for water .It reduces the

swelling characteristics of the soil .

3.6.2.3. FLY ASH STABILIZATION: Fly

ash is a by product of the pulverized coal

combustion process. Fly ash has silica,

alumina and various oxides and alkalis as its

constituents .It is fine grained and

pozzolanic in nature. Fly ash reacts actively

with hydrated lime and hence is used in

combination with lime as a stabilizer. A

mixture of about 10 to 35 % of fly ash and 2

to 10 % of lime forms as effective stabilizer

for stabilization of highway bases and sub

bases .Soil-lime-fly ash mixes are

compacted under controlled condition with

adequate quantity of water.

3.7. GEOTEXTILES: Soil conditions can

be improved in an excellent manner by

using geo textiles. Geotextiles are porous

fabrics manufactured products and others

such as polyester ,polyethylene,

polypropylene and polyvinylchloride, nylon,

fiber glass and various mixtures of these.

These are having permeabilities comparable

in range from coarse gravel to fine sand.

Geotextiles have been used in a

variety of civil engineering works. Thus

in the selection of a proper geotextile,

due importance has to be given to the

major function that the geotextile is

intended to perform. These are majorly

used as follows.

1. They acts as separators between

two layers of soils having a large difference

in particle size to prevent migration of small

size particles into the voids of large size

particles

2. They act as filter. When the

silt laden turbid water passes through the

geotextile, the silt particles are prevented

from movement by the geotextile.

3. Geotextiles themselves function

as a drain because they have a high water

transporting capacity than that of the

surrounding material.

4. They serve as REINFOREMENT

in soil since they are a good in tensile

strength.

3.7. ELECTRO OSMASIS AND

ELCTRO CHEMICAL HARDENING

METHOD:

The electroosmasis process can

be used to increase the shear strength

and reduce the compressibility of soft

clayey and silty soils beneath

foundation. By introducing an

electrolyte such as calcium chloride at

the anode, the base exchange reaction

between the iron anode and surrounding

soil is increased, resulting in the

formation of ferric hydroxides which

bind the soil particles together. However

because cost of electric power and

wastage of electrodes, electroosmasis

with or without electrochemical

hardening can be considered only for

special situations where the alternative

of piling cannot be adopted.

4. CONCLUSION:

1. Unfavorable soil conditions can

frequently be improved using

soil improvement techniques. A

variety of soil improvement

techniques have been developed.

However a suitable technique has

to be adopt according to

necessity of the structure and

economy.

2. Mainly soil improvement

techniques can be divided in to

four broad categories;

Densification technique,

Reinforcement technique,

grouting or mixing technique and

stabilization technique.

3. Densification is probably the

most commonly used soil

improvement technique. Most

densification techniques relay on

tendency of granular soils to

densify when subjected to

vibrations. However there is a

possibility of damaging adjacent

structures and pipelines due to

application of this technique.

4. Reinforcement techniques introduce

discrete inclusions that stiffen

and strengthen a soil deposit. The

high stiffness and strength of the

inclusions also tend to reduce the

stresses imposed on the weaker

material between the inclusions.

5. Grouting techniques involve the

injection of cementitious

materials into the voids of the

soil or into fractures of the soil,

so that the particle structure of

the majority of soil remains

inject. In permeation grouting,

very low viscosity grouts are

injected intothe voids of the soil

with out disturbing the soil

structure. In intrusion grouting,

thicker and more viscous grouts

are injected under pressure to

cause controlled fracturing of the

soil.

6. Now a days, geotextiles are

extensively used for improving

the soil conditions. These has

multiple applications as they act

as filters, reinforcement,

separations..etc.

5. BIBILOGRAPHY:

1. “Geotechnical Engineering

Principles & Practices” by Donald

P.Coduto

2. “Foundation Design &

Cinstruction “by M.J.Tomlinson.

3. “Geotechnical Engineering” by

Purshotham raj

4. “Geotechnical Earthquake

Engineering” by Steven

L.Kramar.

.