Problematic Soil and Ground Improvement Techniques

Report on

Problematic Soil and Ground

Improvement Techniques

SUBMITTED TO:

Engr. Ussama Waseem

SUBMITTED BY:

Abdul Moeez (13L-5779)

Asad Abdullah (13L-5770)

Aqib Rana (13L-5800)

Afzaal Akram (13L- 5815)

Hassan Khalil (13L-5792)

DATE OF SUBMISSION:

May 26, 2016

ORGANIZATION:

FAST NUCES DEPARTMENT OF CIVIL ENGINEERING

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Table of Contents ABSTRACT ................................................................................................................................................. 6

INTRODUCTION ....................................................................................................................................... 7

SOIL: ........................................................................................................................................................ 7

Importance of soil in construction ......................................................................................................... 7

PURPOSE .................................................................................................................................................... 7

EXPLANATION ......................................................................................................................................... 8

Problematic Soil: ..................................................................................................................................... 8

Types of problematic soil: .................................................................................................................. 8

Chemical soils: ......................................................................................................................................... 8

Acidic Soil: ................................................................................................................................... 8

Saline soil ...................................................................................................................................... 9

Alkaline soil ................................................................................................................................ 10

Sodic Soil .................................................................................................................................... 11

Physical soils: ......................................................................................................................................... 12

Dispersive soil ............................................................................................................................. 12

Collapsible soil ............................................................................................................................ 14

Expansive (swelling) soil ............................................................................................................ 15

Sandy Soil ................................................................................................................................... 17

Hardpan Soil ............................................................................................................................... 17

Laterite Soils ............................................................................................................................... 18

Shock sensitive soil ..................................................................................................................... 18

Frost sensitive soil ....................................................................................................................... 18

Ground Improvement Technique: ...................................................................................................... 19

Types of Ground improvement techniques..................................................................................... 20

Mechanism of Ground improvement techniques ........................................................................... 20

Mechanical techniques .......................................................................................................................... 20

o Remove and replacement of soil ................................................................................................. 20

o Vibro flotation. ............................................................................................................................ 21

o VIbro Reduction .......................................................................................................................... 22

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o Dynamic Compaction. ................................................................................................................ 24

o Compaction Piles ........................................................................................................................ 24

o Grouting ...................................................................................................................................... 25

o Vacuum consolidation................................................................................................................. 27

o Rigid Inclusion ............................................................................................................................ 28

o Pre loading .................................................................................................................................. 29

o Vertical drains ............................................................................................................................. 29

o Ground freezing .......................................................................................................................... 31

o Blasting ....................................................................................................................................... 31

o Wet soil mixing ........................................................................................................................... 32

Chemical techniques: ............................................................................................................................ 33

o Addition of lime .......................................................................................................................... 33

o Addition of sulfates ..................................................................................................................... 34

o De-salinization: ........................................................................................................................... 34

o Addition of gypsum: ................................................................................................................... 35

o Addition of fly ash. ..................................................................................................................... 35

RESEARCH METHODOLOGY ............................................................................................................ 35

CONCLUSION AND RECOMENDATIONS ........................................................................................ 36

BIBLIOGRAPHY ..................................................................................................................................... 37

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List of Figures

Figure 1a. Soil .............................................................................................................................................. 7

Figure 1b. Soil excavation ............................................................................................................................ 7

Figure 2 Acidic soil ..................................................................................................................................... 9

Figure 3. pH scale for soil in Geotechnical field.[1] ..................................................................................... 9

Figure 4. Saline soil .................................................................................................................................... 10

Figure 5 Sodic soil dry texture .................................................................................................................... 12

Figure 6. Sodic soil with cracks .................................................................................................................. 12

Figure 7. Sink hole ..................................................................................................................................... 13

Figure 8.Soil layer dispersion and cracking ................................................................................................ 13

Figure 9. Collapsing soil under the road ..................................................................................................... 14

Figure 10. Cracks on the soil due to expansion ......................................................................................... 16

Figure 11. Expansion cracks on soil ........................................................................................................... 16

Figure 12. Sandy soil ................................................................................................................................. 17

Figure 13 . Texture of sandy soil ................................................................................................................ 17

Figure 14. Hard pan soil layer ..................................................................................................................... 17

Figure 15. Laterite soil ................................................................................................................................ 18

Figure 16. Cracks on pavement due to frost heaving .................................................................................. 19

Figure 17. Soil removal ............................................................................................................................ 21

Figure 18. Soil replacement ........................................................................................................................ 21

Figure 19. Mechanism of vibro-flotation .................................................................................................... 22

Figure 20. Vibro Flotation ........................................................................................................................ 22

Figure 21.Vibrating probe ........................................................................................................................... 22

Figure 22. Steps for Top feed vibro- reduction ........................................................................................... 23

Figure 23. Step for bottom feed vibro- reduction ....................................................................................... 23

Figure 24. A crane doing dynamic compaction .......................................................................................... 24

Figure 25. Steps for compaction pile installation ....................................................................................... 25

Figure 26. Displacement pressure grout ..................................................................................................... 26

Figure 27. Displacement soil fracture grouting........................................................................................... 26

Figure 28. Rock fissure grouting................................................................................................................. 26

Figure 29. Vacuum consolidation ............................................................................................................... 27

Figure 30. Rigid inclusions ......................................................................................................................... 28

Figure 31.Pre loading diagram .................................................................................................................... 29

Figure 32. PVD Core .................................................................................................................................. 30

Figure 33.Compairison between soil with and without drainage paths ...................................................... 30

Figure 34. Ground freezing ....................................................................................................................... 31

Figure 35. Ground freezing ......................................................................................................................... 31

Figure 36. Wet soil mixing ......................................................................................................................... 32

Figure 37. Drainage path for De salinization .............................................................................................. 34

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List of Tables

Table 1. Percentage of collapsing and its intensity ..................................................................................... 16

Table 2. Amount of Agricultural lime depending upon pH and soil texture .............................................. 33

Table 3. Improvement techniques for problematic soils ............................................................................. 36

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ABSTRACT The soil is an essential and second most abundant component of earth. Most of the world activities are

directly or indirectly related to land. The soil is helpful to humans in many ways such as natural water

filtration system, absorbing minerals, constructing shelter/homes and roads, and providing food through

agriculture. In this paper, the reader is being educated with soil having physical and chemical problems in

nature and their types such as changes in pH value and water moisture. The possible remedies of all the

problems are under consideration and improvement techniques that are being used in the world to make

the soil more suitable and stable to use for the purpose of farming, agriculture, and construction. The

ground improvement techniques are used to improve unfavorable conditions of soil to favorable

conditions. The adverse conditions of soil are collapsing, salinity, sodicity, sandy soil, hardpan, sandy

soil, etc.

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INTRODUCTION

SOIL:

The soil is a mixture of materials such as organic compounds, water particles, very small rocks,

microorganisms and decomposed dead matter. The combination of all of this makes the soil altogether.

The soil is covering the top layer of the earth. It is normally brown in color and in providing a base for

plantation and also a bed for the foundation of different building structures. The soil is a porous structure

and can allow water to pass freely through it. This passage due to porosity is the reason how plant’s root

get their water from the soil. Soil can be consolidated as well to remove all the air pockets from the soil.

This compaction can be primary consolidation or secondary consolidation. There is a different category of

soils, depending upon the size such as silt, clay, etc. Silt and clays have the finest particles. The soil is

transported from one place to the other through many natural transportation methods, like with rain, it

mixes with water and flows with it, and water takes the soil to different places and thus it is transported,

and this soil will settle there as the water evaporates leaving the soil behind. The second method is a

storm, the wind, and high-pressure air. The air will take the soil particles and transport this soil to

different places. Other reason of soil transportation can be the work of gravity where the soil particles can

move from high altitude areas to low altitude areas.

Importance of soil in construction

Soil provide a base for the foundation of every construction on earth. So the properties of soil are very

much important for the construction point of view. Because whole building can collapse just because of

the soil. The soil can withstand the load of the building without any failure, but it can fail if the analysis

of the soil, in which the foundation is being placed, is not properly done.

Figure 1a. Soil Figure 1b. Soil excavation

PURPOSE

The purpose of this research paper is to identify all the problems that can occur in a soil, physically or

chemically and to provide a solution to those problems to improve that problematic soil for construction

and another dynamic usage.

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EXPLANATION

Problematic Soil:

Sometimes, due to some unforeseen reasons, the soil starts to expand or swell or can have unexpected of

the settlement, or can collapse. Due to some reasons, the structure of soil fabric can also change thus

altering the strength of soil. All of these can create a lot of problem for construction point of view. The

soil cannot be used for construction purposes and thus need some improvement techniques. Such soils are

known as problematic soils.

Types of problematic soil:

There are two types of problematic soils, chemical soils, and physical soils.

CHEMICAL SOILS

When the problem in the soil is due to the excess chemical amount, then it is known as chemical

soil. There are following types of chemical soils.

o Acidic Soil

o Saline Soil

o Alkaline soil

o Sodic Soil

PHYSICAL SOILS

When the problem in the soil is due to the physical properties of soil. Then this type of

problematic soil is known as Physical soil. Following are the types of physical problematic soil.

o Dispersive soils

o Collapsible soils

o Expansive ( swelling) soils

o Laterite soil

o Sandy soils

o Hardpan soil

o Shock sensitive soil

o Frost sensitive soil

Chemical soils:

Acidic Soil:

Acidity is a property measured by the amount of hydronium ions present in the solution. More

hydronium ions mean more acidic and fewer hydronium ions mean less acidic or alkaline. Acidity is

measured on a pH scale. This scale ranges from 1-14 pH value; one means super acidic; pH value 7

means neutral and pH value 14 means super alkaline. Now if the pH of something is less than seven,

then it is acidic, and if it is more than seven, then it is basic or alkaline. In the case of soil, the soil

becomes acidic if its pH value is less than 7. Soil should have pH above 5.5 for the top layer and

above 5 for sub-layer.

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Effect:

Acidic soil is not recommended for construction point of view because if the soil is more acidic, it can

cause corrosion to different building construction parts that are in contact with the soil. These

construction parts are mostly cast iron, steel, etc. Mostly neutral soil is recommended for construction

purposes because any change in pH can further affect the construction workability and usage of the

soil. Also Shrinkage limit, plastic limit and liquid limit increase if the soil is more acidic.

Causes

Soil become acidic due to a certain number of factors.

Decomposition of acidic plants, insects etc.

Excessive use of fertilizers and pesticides on the soil that was used for agricultural

purpose,before the construction purpose.

Acidic Rain can also cause the soil to become acidic.

Breakdown of much organic matter and minerals.

Excess rainfall can wash out base cations thus increasing the hydronium ions, and increasing

the PH.

Figure 2 Acidic soil Figure 3. pH scale for soil in Geotechnical field. [1]

Saline soil

The excessive amount of salts present in the soil when mixed with water and travel to the surface of

the soil, this soil is known as saline soil. The saline soil has mostly sodium chloride present in it.

Other salts such as magnesium chloride (MgCl2), potassium chloride (KCl), gypsum (CaSO4.2H2O),

sodium sulfate (NaSO4.2H2O) and magnesium sulfate (MgSO4) can also be present. This process of

increasing of salt content is known as salinization.

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Effect:

The effect of salinity is that it decreases the moisture content of the soil and makes it dry and rough.

Moreover the unit weight of the soil increase with the increase in salinity. The unit weight is weight

per unit volume. Also, saline soil has further physical problems such as high compressibility, low

bearing capacity, and more expansion. More salts can increase undrained shear resistance of the soil.

Cause:

Soil become saline due to following reasons:

Salinity is due to minerals and rocks weathering process. With time the mineral and salt

rocks break down into smaller pieces due to a natural condition and mix with the soil and

thus increasing the salt content in the soil and causing the salinity of soil to increase,

making soil saline.

Ocean water also consists of number high number of salts. So ocean water during high

tides comes in contact with the soil layer near it and then water evaporates leaving the

salts behind. This is the reason why soil near is ocean is mostly saline.

Irrigation process can also make the soil saline. Soil that was once used for agricultural

purpose before construction can be saline because during irrigation, roots only absorbed

water leaving salts of water in the soil behind because every water source has some salts

present in it.

Figure 4. Saline soil

In the above figures, white layer on the top of the soil is a salt layer. This layer can be removed to remove

excess salts.

Alkaline soil

Alkaline soil is a property of soil that is measured with a pH scale. This scale ranges from 1-14. pH

value 1 means super acidic; pH value 7 means neutral and pH value 14 means super alkaline. Now if

the pH of something is less than 7 then it is acidic and if it is more than 7 then it is basic or alkaline.

Soil is an alkaline soil if its pH is more than 7. More pH means fewer hydronium ions and more

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hydro oxide ions. The main components that are present in the alkaline soil are sodium carbonates

and sodium bicarbonates.

Effects:

The effect of alkali in soil is almost opposite to that of acid in the soil. Alkaline soil has less shrinkage

limit, plastic limit, and liquid limit. Unit weight of alkaline soil is less than the unit weight of acidic

soil. Unit weight is weight per unit volume.

CAUSE

The causes of alkali soil are

Sodium carbonates and bicarbonates rock breakdown due to weather conditions.

Naturally occurrence of Sodium carbonates and bicarbonates in the soil.

Sodic Soil

The sodic soil is a type of soil. This soil has a high concentration of exchangeable sodium percentage

present in it, and less concentration of other salts present in it. Sodium is a positive cation. It will

weaken the physical properties of soil. Cations weaken the bond between the particles of soil and they

will swell and disperse.

Effect:

The effect of the sodium salt is that it decreases the moisture content of the soil and makes it dry and

rough. The sodic soil also degrades the soil structure and thus leading to a physical problem known as

soil dispersion. Sodic soil can also have wind and water erosion. Sodic soil can also cause the soil to

swell.

Cause:

Soil becomes saline due to following reasons:

Sodic soil can be due to increasing in groundwater level that has sodium present in it.

Mostly the source of sodic soil is natural.

Irrigation process can also make the soil sodic. Soil that was once used for agricultural

purpose before construction can be sodic because during irrigation, roots only absorbed

water leaving salts and other metals of water in the soil behind because every water

source has some sort of salts and light metals present in it.

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Figure 5 Sodic soil dry texture Figure 6. Sodic soil with cracks

Physical soils:

When the soil becomes problematic due to change in the physical properties of soil, this is known as

physical soil.

Dispersive Soil

Dispersive soils have a physical failure. The name has a word disperse in it. Disperse means to spread

apart, move away. Similarly in this soil, the soil surface breaks and spreads apart. This is due to the

weak bond between the particles of the soil and clay etc. This condition occurs due to higher

exchangeable sodium percentage in the soil. Sodium is a cation and it will weaken the bond between

the soil particles. The repulsive forces between the soil particles become stronger than the force of

attraction. Due to which, the soil particles will move away as far as possible and they will spread and

thus creating cracks on the surface of the soil. This is also known as sodic soil. A soil having more

exchangeable sodium percentage in it is known as sodic soil. The soil first becomes sodic and then it

disperses. So a soil that is dispersive is also sodic soil. Dispersive soils contain a moderate to the high

content of clay material, but there are no significant differences in the clay fractions of dispersive and

non-dispersive soils, except that soils with less than 10% clay particles may not have enough colloids

to support dispersive piping.

Effects

The effects of dispersive soils on the construction point of view is very important. As we know that the

sodium is a positive cations so it will increase the repulsive forces between the soil particles and will

decrease the force of attraction between the soil so as a result, the dispersive soil and clays will spread

apart from each other thus this will weaken the surface of soil it will erode in air and water, and it will

have higher compressibility under load. Besides this weak surface, dispersive soil can also have tunnel

formation and sinkholes underneath the layer of soil. Thus, we cannot use a dispersive soil for the

construction because it is affected and cannot fully take the load and will fail and settle down under load.

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Mechanism

Soil /Clay particle

Na Na

Na

Na

Soil/ Clay Crystals

The above illustration shows that how 2 particles of soil separate from each other when sodium cation

comes between them.

TEST

There are following test for the dispersive soil to check whether a soil is dispersive or not.

Crumb test

Pinhole test

Chemical test

Double hydrometer test

Figure 7. Sink hole Figure 8.Soil layer dispersion and cracking

d

d

N

a

Force of repulsion

between the particles

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Collapsible soil

A type of soil that is moisture sensitive is known as collapsible soil. This type of soil will carry a heavy

load and will stay like that until it comes in contact with the moisture. As soon as it comes in contact with

moisture, the strength of the soil decreases and the volume of the soil will decrease and the soil will have

a very high settlement and thus, it will fail and will collapse. This type of soil becomes weak when it

comes in contact with moisture, mainly water.

Mechanism

The reason behind such collapsing is the structure of the soil particles. These soils have a very high void

ratio and low density. Now this will have the web like structure inside it when it is in dry condition and

will bear heavy load without any settlement. However when the soil becomes wet, all the water particles

will move inside the voids of the soil and the web-like structure will break, and soil particles will

rearrange itself for the saturation state of the soil. This rearrangement of soil structure will cause the soil

to settle down at a high speed and thus, the soil will collapse.

Effects

The effect of collapsing soil is very adverse and it can or cannot be used for the construction purpose. The

choice of soil depends on upon the fact that whether the foundation of the building will be exposed to

moisture or not. Its volume reduction property under water contact can cause sudden settlement and

collapse that can be fatal for any sort of construction over it. It must be treated before using for

construction purpose so that it can bear the load and will not reduce in the volume under moisture from

building and surrounding and thus causing failure.

Source

Most of these types of soil consisting of wind dispersed sand and silt with a small percentage of

clay as cohesive materials. One of the characteristics of these soils that have relatively low dry

density and unsaturated.[15]

Soil particles produced from weather process of rocks and other minerals can also act as

collapsible soil. As those particles are newly dispersed from the surface from the surface of parent

rock or mineral, it will settle down and will form a layer of soil that will be unsaturated and will

have a large number of voids.

Figure 9. Collapsing soil under the road

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Expansive (swelling) soil

This type of soil is opposite to collapsible soil. As in the collapsible soil, the volume of the soil reduces as

it comes in contact with the water. In this type of soil, the volume of the soil generally increases as it

comes in contact with water and shrink when the water leaves the soil. This type of soil acts like a sponge.

As the volume of the soil increases, it will exert a certain pressure on the building on any constructed

material on top of it and can cause cracks on it.

Mechanism

The mechanism of this type of soil is very simple. These type of soil have a clay mineral known as

“Montmorillonite”. This mineral has the ability to attract the water particles and fill the gap with water

particles and thus overall increasing the volume. The clay particles are –ve charged.

STEP 1:

Clay particle

Clay particle

STEP: 2

Clay particle

Clay particle

STEP 3

Clay particle

Clay particle

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Gap between

two clay

particles

Water molecules

moving toward the gap

between the clay

particles

Water particles fills the

gap between the

particles of soil and

thus pushing them a

bit away increasing the

overall volume.

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Effects

Expansive soil is very much destructive for the construction as it can produce some adverse effect on the

soil layer. The obvious way an expansive can damage a building foundation of anything that is created

over such soil is by the uplift due to increase in the volume of the soil. This uplift motion of the soil can

put a pressure on the above construction and thus causing cracks to develop on them. The water can enter

in the soil during a raining season through the cracks on the surface of soil due to dry weather. This water

will increase the volume of the soil under the foundation and the soil under foundation expands and will

exert a pressure on it that can leads movement of foundation and thus whole building can collapse.

% Collapse Intensity of problem

0-1 No Problem

1-5 Moderate problem

5-10 Problem

10-20 Severe problem

More than 20 Very severe trouble Table 1. Percentage of collapsing and its intensity

Cause

This is due to a clay mineral known as “Montmorillonite”. This mineral has the ability to attract

water particles to fill the gaps.

Figure 10. Cracks in the soil due to expansion Figure 11. Expansion cracks on soil

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As the water exit the soil, it will shrink and comes to its natural normal volume but the cracks that were

developed during the expansion of soil still stays there and it will take a lot of time to naturall fill those

cracks before another expansion.

Sandy Soil

The name suggests, a type of soil that has all the particles of sand present in it. This type of soil has very

large particles and minimum to no clay present in it. This type of soil is granular. In its composition, it has

almost 70% sand, 30% silt and clay.

Effect

As the sandy sand has granular particles and particles have larger size so they do not perform the required

compaction that is performend by the clay and silt in the soil. That is why sandy soils are not

recommended for construction. However they can be used when there is no any other soil available.

Figure 12. Sandy soil Figure 13 . Texture of sandy soil

Hardpan Soil

This type of soil layer is present under neath the top layer. This soil has become compacted and hard due

to consolidation under very heavy loading of construction building. This soil layer has poor drainage for

water because of compaction. However this soil is good for foundation purpose.

Figure 14. Hard pan soil layer

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Laterite Soils

In tropical areas, heavy rainfall can cause weathering of igneous rocks. This weathering will dispose

small particles of rocks and minerals to mix with the soil thus forming a red colored soil structure. This is

known as laterite soils. Now this igneous mineral will decrease the density of soil. This soil has large

amount of water moisture present inside it.

Effect

If this laterite soil is used for construction, then the soil becomes soft and very saturated because of

already water moisture present in it. This soft soil will give unsatisfactory results for construction and

must be improved or repaired before using. Usually the soil near igneous rocks are laterite soil.

Figure 15. Laterite soil

Shock sensitive soil

It is also known as soil liquifaction. If a soil has no binding or cementing material to hold them together

then it is shock sensitive soil. Shock sensitive soil is that soil that will rearrange itself and will compact

and settle under any sort of shock or vibration. These vibration or shock can be due to Earthquake, bomb

blast and pile driving. This type of soil is found under the ground near water table where there is pure

clean soil without any binder or cement.

Effects

This layer is loose. However if a foundation or a pile is supported on this layer of soil and this soil will

start compacting due to vibration or shock, then the soil will start to densify and compact and at this time,

it wont support the foundation or pile and thus will fail and cause the whole building to fail.

Frost sensitive soil

This type of soil problem is common in cold freezing seasons. During freezing temperature, the water

moisture in the soil will freeze and thus when water freezes, its volume is increased by 9%.

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Effect

When the water moisture freezes in the soil, it will increase in volume by 9% and thus create a pressure in

it surrounding soil layer because of more space coverage. This will move the soil and thus as a result the

soil layer will move and all the building construction will get the cracks on the surface because of

movement of soil layer. However when the water unfreezes, the soil particles rearrange theselves and go

back to initial position but cracks remain the same.

‘

Figure 16. Cracks on pavement due to frost heaving

Ground Improvement Technique:

Ground improvement techniques are technique that are used to modify the ground properties in order to

achieve the favorable ground conditions for a particular purpose such as densification of soil, accelerating

the consolidation, usage of admixture etc. All of these techniques have a single purpose to stabilize the

soil for construction use.

Ground improvement techniques are used to improve following problems from the soil.

Increase in soil load bearing capacity by making it denser.

Reduction in the soil settlement

Reduction of liquefaction during earth quake shaking.

Reducing large amount of pore water pressure.

Avoiding shrinkage and expansion.

To avoid soil liquefaction (shock sensitive soils).

No ground lowering or excavation

To improve the pH of soil.

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Types of Ground improvement techniques

There are three types of ground improvement or soil stabalization techniques.

Mechanical improvement techniques

Chemical improvement techniques

Mechanism of Ground improvement techniques:

There are 4 mechanism by which a ground is improved.

Compaction.

De watering.

Admixtures.

Reinforcement.

Mechanical techniques

Mechanical techniques are the oldest techniques that are used to stabilize the soil layer. It involves the

improvement of soil by physically changing its structure. This can be done in many ways. Following are

the mechanical techniques.

Remove and replacement of soil.

Vibro Flotation.

Vibro Reduction.

Dynamic Compaction.

Compaction Piles.

Grouting.

Vacuum consolidation.

Rigid Inclusion.

Pre-loading technique.

Vertical drains

Ground freezing.

Blasting

Wet soil mixing

o Remove and replacement of soil

One of the oldest method of ground improvement technique. In this method we simply remove the

affected soil layer and then replace this layer with a layer of soil that has no problem whatsoever. This

excavated affected soil can then be used for back filling purpose. This method is simple and useful

and require very less machinary but it has some problems as well.

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This method is not applicable on wet soil as it is difficult to excavate and remove wet soil in semi

liquid form.

We can only remove layer of soil till the ground water level.

Due to such limitations, this method is used only when there is necessity otherwise we avoid this

method and use other methods.

Soil Improvement :

This method can improve any sort of soil problem as we are replacing the soil with a new soil layer so

any sort of problem can be dealt with this method.

Figure 17. Soil removal Figure 18. Soil replacement

o Vibro flotation.

Vibroflotation is also known as vibro compaction. This is compaction of soil with the help of

vibrating probe.A vibrating probe is inserted in the granular soil about 100 meter deep. The probe

vibrates as it move down and thus causing the surrounding granular structure to collapse and fill the

gap thus making the soil denser.This method is used where the soil structure is not that much dense

and require more density and also for soft soil stabilization. It is also applicable for granular soils as

well.

Mechanism:

Its basic principle is compaction of soil layer. Mechanism of vibro flotation is simple. The Vibrating

probe is inserted the ground making a bore hole. This probe will vibrate causing the soil granules in

the surrounding of the bore hole to loosen themselves and back-fill bore hole thus making the soil

more denser.

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Figure 19. Mechanism of vibro-flotation

Improvement:

This method is used to densify the soil layer. By densifying the soil layer, we can

Increase its load bearing capacity

Reduces the voids that can avoid collapsing and expansion.

Reduce settlement of soil.

Avoid soil liquifaction. `

Figure 20. Vibro Flotation Figure 21.Vibrating probe

o VIbro Reduction

This is an extension of vibro-flotation. It is also known as stone columns.This method is used to densify

the soil layer at a particular area.It is used where the soil particles are more cohesive and they do not back

fill the bore hole due to vibration to densify the ground during vibration.In this method, aggregate is

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compacted in the hole ,by vibrating probe, in the form of column to increase the strength and stabilize the

soft soil problem. It is fast and economical for deep compaction.

There are two types

Wet/Top feed:

In this method, penetration in soil is done through and soil is examined. Then filling of aggregates is done

with compaction. Then granular is filled and consolidated to complete the column.

Figure 22. Steps for Top feed vibro- reduction

Dry/Bottom feed:

In this method, penetration in soil is done through and soil is examined. Installation of aggregate is done

through separate duct along the Vibro probe. And consolidation of granular soil is done to finish the

column.

Figure 23. Step for bottom feed vibro- reduction

Mechanism

Its basic principle is compaction and reinforcement of soil layer

Improvement:




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Avoid soil liquefaction. `

o Dynamic Compaction.

In this method, heavy steel or concrete hammer is lifted at 30 to 100ft and dropped in a grid pattern to

densify the soil. This is used to increase the density of soil. Most cheap and economical method. The

hammer is quite heavy and when it hit the ground from a height, it creates an impact loading on the

surface of that will rearrange the soil structure and all of the gaps get filled by the soil particle thus

increasing the density of the soil.

Mechanism:

Its basic principle is compaction of soil layer.

Improvement:





Avoid soil liquifaction

Figure 24. A crane doing dynamic compaction

o Compaction Piles

Compaction piles are usually those piles that are installed in the ground to increase its density and also to

provide reinforcement to increase its strength. Compaction piles are made up of pre stressed concrete.

Mostly micropiles are used for this purpose. A pile is inserted in the affected soil area. This pile will hold

the soil and increase its compaction and also thus increasing the bearing capacity.

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Mechanism:

Its basic principle is compaction and reinforcement of soil layer.

Improvement:





Avoid soil liquifaction.

Figure 25. Steps for compaction pile installation

o Grouting

Injection of slurry material in soil is known as grouting and the material used is known as grout. The

process of grouting is to prevent seepage in soil beneath dams and hydraulic structures by filling voids of

soil. Grout is normally the mixture of water, cement, sand and sometimes fine gravels.

There are various methods of grouting such as:

Permeation Grout: it is impregnating of voids by displacing water and air from the voids and

filling the grout. It is done by injecting a thin layer of grout which dries to form solid mass. In this

grouts are usually chemical compounds.

Displacement Pressure Grout: it injecting of thick, low mobility grout that becomes homogenous

without entering soil. Once the grout expands the surround sand is displaced and densified. It is

normally use to repair structure with excessive settlement.

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Figure 26. Displacement pressure grout

Displacement Soil Fracture Grouting: It is injecting of cement, soil and water into the soil with

high pressure to fracture the soil to form root-like or thin lens shaped zones of grout material in

soil. It increases the densification and macroscopic strength of soil.

Figure 27. Displacement soil fracture grouting

Jet or Replacement-Displacement Grouting: In this technique, a special grout pipe is used called

monitor having high-speed jets of grouts are used to erode and excavate the soil. Thereafter,

strong impervious columns are produced by mixing grout with soil. This process can be used in ll

types of soil.

Rock fissure Grouting: Rock fissure uses a hole drilled through fissures and joints if rock mass to

allow grouts to be injected at close centers vertically and re-injecting if needed.

Figure 28. Rock fissure grouting

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Mechanism:


Improvement:






Avoid seepage.

o Vacuum consolidation.

This method extracts water and air from the soil layer.Suction is induced by the creation of vacuum

on the ground surface.This method is used for improving loosely saturated soil to densify it.The

vacuum causes water to drain out from the soil and creates negative pore water pressure in the soil.

This leads to an increase in effective stress to the magnitude of the induced negative pore water

pressure, without the increase of total stress .

Mechanism:

Its basic principle is compaction and de-watering of soil layer.

Improvement:






Reduce pore water pressure.

Figure 29. Vacuum consolidation

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o Rigid Inclusion

Rigid inclusions is another technique that transfers loads through weak strata to a firm underlying

stratum using high modulus, controlled stiffness columns. A vibrator is used to pierce through weak

strata to place underlying stiff columns. Granular bearing soils are densified by displacement.

Concrete is then pumped through the mandrel, which opens as it is raised. The mandrel may be raised

and lowered several times within the bearing depth to construct an expanded base if required by the

design. The mandrel is then extracted while a positive concrete head is maintained. The concrete fills

the void created by the mandrel during extraction, and terminates in an strong upper stratum or is

subsequently overlain by an engineered relieving platform. The improved performance results from

the reinforcement of the compressible strata with the high modulus columns. The technique has been

used to increase allowable bearing pressure and decrease settlement for planned structures,

embankments and tanks.[14]

Mechanism:


Improvement:






Figure 30. Rigid inclusions

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o Pre loading

It is also known as pre- compression. In this method, vertical stress is applied on the affected soil to

remove water particles form the soil to make soil less compressable and more compacted and to increase

its density and decrease the pore water pressure. Surcharging is an economical method for ground

improvement. However, the consolidation of the soils is time dependent, delaying construction projects

making it a non-feasible alternative.

Mechanism:

Its basic principle is dewatering of soil layer.

Improvement:







Figure 31.Pre loading diagram

o Vertical drains

This process is also known as PVD pre-fabricated vertical drain or band drain technology. It is normally

used for soil having loose, compressible water saturated clay and silty clay. Soil is normally considered

with very loose skeleton and large pore sizes filled with water. This requires huge time for soil to settle or

consolidate on loading. Without vertical drain consolation take place in one direction. Vertical drainage is

longer and takes larger time to consolidate.

In vertical drains, pore water will flow laterally dissipating pore water pressure vertically so water is

conveyed through vertical drains. It takes months for soil to consolidate.

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In PVD there is core which called drained body corrugated and flexible which is made of polypropylene.

It is design to improve design capacity and high tensile and compressive strength. And a filter jacket

thermically bonded polypropylene wrapped around the core which acts as filter to allow ground water to

enter core.

Figure 32. PVD Core

After the installation of band drains settlement is being observed through casagrande piezometer. The

water coming out is collected in temporary ditch and dewatered to adjoin areas.

Advantages:

Minimum disturbance in soil.

Higher water discharge.

Higher tensile strength which prevents collapse.

Easy and fast installation.

Mechanism:

Its basic principle is dewatering of soil layer.

Improvement:







Figure 33.Compairison between soil with and without drainage paths

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o Ground freezing

Ground water freezing is an improvement technique in which refrigerations are used to freeze the

water molecules in the soil. These water ice crystals will then act as a binder and will bind all the

particles to each other thus increasing the strength of soil and avoiding seepage. Pipes are run

throughh the soil and then refrigerants are run through oipes The disadvantage of this method is that

we cannot use this method in hot weather as the ice will turn back to water due to temperature.

Refrigerant is mostly liquid nitrogen.

Mechanism:


Improvement:






Avoid seepage.

Figure 34. Ground freezing Figure 35. Ground freezing

o Blasting

Blasting is another process to increase the density of the soil. It is done by blasting over the affected soil.

The blast layer creates a wave that temporarily liquify the soil particles and thus soil particles rearrange

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themselves and make a compacted and strong surface. It has been used to treat soils to depths of upto

40m.

Mechanism:


Improvement:






o Wet soil mixing

This method is mixing of soil with a binder slurry. In this method, we first drill a hole in the affected soil

area and then add slurry in the hole and then mix the soil in the hole with the slurry to make a binding

bond between slurry and soil. This is used in weak soil area to increase the strength of the soil. The slurry

is injected through feeder pipes. Wet soil mixing is best suited for soils with moisture contents up to 60

percent. Soft cohesive soils are usually targeted as other soil types can often be treated more economically

with other techniques. If the moisture content is greater than 60 percent, dry soil mixing may be more

economical.

Mechanism:

Its basic principle is compaction and admixture of soil layer.

Improvement:






Figure 36. Wet soil mixing

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Chemical techniques:

In this type of techniques, ground quality is improved by adding different chemical compounds in the soil

to reduce the problem. Following methods are used to chemically improve the soil.

Addition of lime.

Addition of sulfates.

De-salinization.

Addition of gypsum.

Addition of fly ash

o Addition of lime

Acidic soil have deficiencies in the following components:

Calcium

Maganisum

Phosphorus

Potassium

To buffer the soil to netural pH, the agricultural lime(calcium carbonate) is added to acidic soil, and its

amount vary with the amount of present acidic pH of the soil. In normal practice, 12 g/m2 for clay soil and

30 g/m2 for sandy soil is added and then its is tested again after few months, if still the soil has not

reached it optium pH then more is added. Using agriculture is cheaper way to improve pH. Sometimes

soil with large amount of calcium or magnesium present, altenative agriculture is used for balancing.

Table 2. Amount of Agricultural lime depending upon pH and soil texture

Addition of lime to increase pH.

Mechanism:

Its basic principle is admixture of soil layer.

Soil Texture pH 4.5 to 5.5 pH 5.5 to 6.5

Sand, loamy sand 85 g/m2 110 g/m2

Sandy loam 130 g/m2 195 g/m2

Loam 195 g/m2 240 g/m2

Silty loam 280 g/m2 320 g/m2

Clay loam 320 g/m2 410 g/m2

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o Addition of sulfates

Alkaline soil have deficiencies in the following components:

Iron

Maganese

Copper

Zinc

Boron

Sulphates of iron and ammonium, and organic matters are used to reduce the pH from alkalinity to acidic.

The best way to reduce pH of alkaline soil is to use organic matter that can be added as manure, compost

or green manuring. Organic matter will generally buffer plants against the impact of acidity. Gypsum

(calcium sulphate) does not alter the pH of the soil but improve aeration and reduce compaction.

Mechanism:


o De-salinization:

Drainage is the major method of controlling soil salinity of soil. The system should have proper

irrigation system to allow water to flow continously. The salt concentration in normal soil is 5%

to 10% of drainage water higher than irrigated water which means salt export matches salt

import and salt will not accumulate. In saline soil, the concentration of drained soil is much

higher than irrigated soil which means salt export will be higher than salt import. So with proper

drainage a rapid desalinization occurs. After few years, the soil salinity is decreased so much,

that the salinity of the drainage water has come down to a normal value and a new, favorable,

equilibrium is reached.

Figure 37. Drainage path for De salinization

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Mechanism:


o Addition of gypsum:

High sodicity causes clay to swell excessively when wet. The clay particles move so far apart that they

separate (disperse). This weakens the aggregates in the soil, causing structural collapse and closing-off of

soil pores. Lime compound (calcium carbonate), such as gypsum, is a compound that contains calcium.

Therefore, it contributes to reducing the effects of sodicity.

Mechanism:


o Addition of fly ash.

Fly ash is a byproduct from burning pulverized coal in power generating plants. When the fly ash is

added to the soil, it increases the bearing property and strength of the soil and make it stabilize.

Furthermore fly ash act as a drying agent and absorb excessive moisture content present in the soil.

Mechanism:


RESEARCH METHODOLOGY

The research methodology is basically simple. The source of this research paper are basically

geotechnical engineering books, internet, research papers and instructor. The concept has been taken

from such sources and is written in simple own words. The main task was to gather correct concept so

that it can be delivered correctly. The only issue was to analyze so much data, as the topic is broad

and wide.

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CONCLUSION AND RECOMENDATIONS

As it is observed above that soil has very much importance in our construction point of view. So it is

important that soil should be according to our requirement to bear the load. We have studied the possible

problems in the soil and the reason of such problems. We have also studied about the solution techniques

to solve such problems. Following table is extracted from above data.

Type of soils and problems Improvement technique

Cohesive soils Vertical drain, Wet soil mixing, Vibro reduction,

Vacuum consolidation

Cohesion less soils Compaction, Micro piles, Grouting, Vibro

reduction.

Collapsible and expansive soil Vibro reduction, Vibro flotation, Vacuum

consolidation, compaction, piles, Blasting.

Soil liquefaction Vertical drains, Vacuum consolidation, Dynamic

compaction, piles, Vibro flotation, Vibro

reduction.

Acidic, Alkaline and salty soils Drainage and Addition of chemicals

Low dense soil Vibro reduction, Vibro flotation, Vacuum

consolidation, compaction, piles, Blasting. Vibro

flotation Table 3. Improvement techniques for problematic soils

All of the soil problems in the end cause above mentioned problems so in order to improve such soil, it is

recommended to provide recommended improvement techniques.0

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BIBLIOGRAPHY

1. Z. Chik , T. Islam, 2011, Study of Chemical Effects on Soil Compaction Characterizations

Through Electrical Conductivity, Int. J. Electrochem. Sci , 2

2. B. Indraratna, C. Rujikiatkamjorn, J. S. Vinod, and S. Nimbalkar, 2011, Physical and chemical

ground improvement for sustainable transportation infrastructure under cyclic loads, School of

Civil, Mining and Environmental Engineering, University of Wollongong, 4-11

3. Mohsen Rezaei1, Rasoul Ajalloeian, Mohammad Ghafoori, 2012, Geotechnical Properties of

Problematic Soils Emphasis on Collapsible Cases, International Journal of Geosciences, 1-2

4. F.G.Bell, M.G.Culshaw,2001,Problem soils, Thomas telford, 2-8

5. M.M.Ali, 2010, Identifying and Analyzing Problematic soils, Geotech Geol Eng, 1-2

6. James D. Hussin, 2006, Methods of Soft Ground Improvement, Taylor & Francis Group, 531-560

7. Patra, N. R. (Nihar Ranjan), 2014, Ground Improvement Techniques, National Programme on

Technology Enhanced Learning (NPTEL),

8. M.P Moseley and K.Kirsch, 2004, Ground improvement, Spon press, 4-220

9. Gaafer,Manar, Bassioni,Hesham, Mostafa,Tareq, 2015, Soil Improvement Techniques,

International Journal of Scientific & Engineering Research, 1-5

10. Colin.J. Serridge, 2006, Some applications of ground improvement techniques in the urban

environment, IAEG, 3-4

11. Latest techniques in ground improvement techniqes,, Retrieved from

http://theconstructor.org/geotechnical/latest-trends-in-ground-improvement-techniques/1836/

12. Soil improvement techniques, Retrieved from

http://www.ce.washington.edu/~liquefaction/html/how/soilimprovement.html

13. Solutions to Soil Problems: High Salinity, Retrieved from

http://articles.extension.org/pages/63502/solutions-to-soil-problems:-high-salinity

14. Rigid Inclusions (Controlled Stiffness Columns), Retrieved from

http://www.haywardbaker.com/WhatWeDo/Techniques/GroundImprovement/RigidInclusions/

default.aspx

15. Higher Technological Institute, Retrieved from http://www.hti.edu.eg/academic-

files/Arabic/1836.pdf

http://doer.col.org/browse?type=author&value=Patra%2C+N.+R.+%28Nihar+Ranjan%29

http://theconstructor.org/geotechnical/latest-trends-in-ground-improvement-techniques/1836/

http://www.ce.washington.edu/~liquefaction/html/how/soilimprovement.html

http://articles.extension.org/pages/63502/solutions-to-soil-problems:-high-salinity

http://www.haywardbaker.com/WhatWeDo/Techniques/GroundImprovement/RigidInclusions/default.aspx

http://www.haywardbaker.com/WhatWeDo/Techniques/GroundImprovement/RigidInclusions/default.aspx

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Documents

Problematic Soil and Ground Improvement Techniques