VISVESVARAYA TECHNOLOGICAL UNIVERSITY

“JNANA SANGAM”, BELAGAVI-590018

TECHNICAL SEMINAR REPORT

Submitted in Partial Fulfilment for the award of Degree of

Bachelor of Engineering
In

CIVIL ENGINEERING
Submitted by

ARADHANA (1BI16CV020)

Under the guidance of

Mr. GANGADHARA S.
(Assistant Professor)

Bangalore Institute of Technology

K R Road, V V Puram, Bangalore-560004
 BANGALORE INSTITUTE OF TECHNOLOGY
K.R.Road,V.V.Puram, Bangalore – 560 004

DEPARTMENT OF CIVIL ENGINEERING

CERTIFICATE

This is to certify that the TECHNICAL SEMINAR having subject code 15CVS86 is
carried out by ARADHNA bearing USN 1BI16CV020, a bonafide student of
Bangalore Institute of Technology in partial fulfillment for the award of Bachelor of
Engineering Degree in CIVIL ENGINEERING from Visveswaraya Technological
University, Belagavi, during academic year 2019 – 2020. It is certified that all
suggestions indicated have been incorporated in the report. This Internship Report has
been approved as it satisfies the academic requirements in respect of Internship work
prescribed for Bachelor of Engineering.

Signature of the Guide Signature of HOD

Mr. GANGADHARA S. Dr. H.B.Balakrishna
Assistant Professor Head of Department

Dept. of Civil Engineering Dept. of Civil Engineering

 Acknowledgement

The satisfaction and euphoria that accompany the successful completion of any task would
be incomplete without the mention of people who made it possible and under whose
constant guidance and encouragement the task was completed.

We are indebted to Dr. M. U Aswath, Principal, Bangalore Institute of Technology,

Bangalore for his support, cooperation and encouraging remarks.

We are grateful to Dr. H.B. Balakrishna, HOD of the Civil Department, BIT Bangalore
for his support and encouragement.

We extend our sincere appreciation to our guide Mr. Gangadhara S. Assistant Professor,
Department of Civil Engineering, Bangalore Institute of Technology who provided his
valuable suggestions and precious time in accomplishing my technical seminar work. His
guidance gave us the environment to enhance our knowledge, skills and to reach the
pinnacle with sheer determination, dedication and hard work.

Last but not the least, we express our heartfelt gratitude to Almighty and our friends who
gave lot of suggestions to complete the internship work successfully.
 ABSTRACT

The technical seminar report in board spectrum contains nine chapters in which we tried
to give an overview about underwater construction. The content of all section is broadly
explained and it is made from the exhaustive study of journals, research papers and other
authentic source.

In first chapter, I have given a brief introduction about underwater construction, its need
in today’s scenario and the materials use for construction. In the second chapter, I have
explained in detail the techniques used in underwater construction. This includes mainly
caisson and cofferdam whose mechanism of work, types and components are explained.

In the third chapter, I have done a specific comparison between the different techniques of
underwater construction.

In the fourth chapter I have discussed the various loads acting on the caisson and their
effect on structure.

Fifth chapter of this report has detailed procedure of different methods involved in
underwater concreting. Like tremie , pumping, hydro valve method etc.

sixth chapter deals with the different underwater concrete properties and how to improve
them. It also gives an overview about the type of concrete to be used for underwater
construction.

Seventh chapter points out the challenges faced during underwater construction and also
in the maintenance of such structures. It also underlines some solution for it.

In the chapter eigth I have wrote the conclusion of my study on underwater construction
and what I learned during this period. Chapter nine contains the references what is used
for making this report.

After reading all the chapters, one can easily understand basics of underwater
construction procedure, its advantages and challenges.
CONTENTS PAGE NO

CHAPTER 1: INTRODUCTION
1.1 Need Of Underwater Construction 01
1.2 Materials Used For Construction 02

CHAPTER 2: TECHNIQUE OF UNDERWATER

CONSTRUCTION
2.1 Cofferdam 04
2.1.1 Cofferdam Types 05
2.1.2 Cofferdam Components 06
2.1.3 Advantages Of Cofferdam 07
2.2 Caisson 08
2.2.1 Types Of Caisson 08
2.2.2 Mechanism Of Caisson 10
2.2.3 Components Of Pneumatic Caisson 10
13
CHAPTER 3: COMPARISON OF CAISSON AND
COFFERDM
14
CHAPTER 4: TYPES OF IMPOSED LOAD
16
CHAPTER 5: METHOD OF CONCRETING
25
CHAPTER 6: UNDERWATER CONCRETE
PROPERTIES
29
CHAPTER 7: CHALLANGES
31
CHAPTER 8: CONCLUSION
32
CHAPTER 9: REFERENCES
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1. INTRODUCTION

At the core, underwater construction is simply industrial construction that happens to take
place under water. Activities vary greatly but include bridge inspection, building repair,
repair of wastewater treatment facilities, and equipment installation.

1.1 Need of underwater construction

Population is increasing rapidly with average growth of 1.6% every year. Traffic
Congestion is one of the major Problems that India is facing and it has a massive impact
on the quality of air, time of travelling, trade and cost. It has been noted that the
government are trying their best In order to come up to this problem by creating
structures Such as Tunnels, Subways, Flyovers and Bridges. But unfortunately it fails as
does not match up with the Increase of population and due to less amount of land
available for the construction.

Fig 1.1: Underwater metro tunnel constructed in Kolkata

In this report there is a Study on the construction of the buildings and structures with a
new technology of constructing under the water. It has been noted that the underwater
buildings exist since Year 1960 but no one was aware of it. The underwater Construction

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of the buildings can be advantageous to the People and the environment if proper
techniques are used and if people get success in achieving such structures. If Such
technology is adapted everything can be built Underwater such as buildings, houses,
shopping complex, Museums, entertainment hub, restaurants, hotels, sports Stadiums etc.
This can lead to a progressive and a Luxurious life to the people and they can even enjoy
their holidays at such places.

Fig 1.2: Ithaa underwater restaurant

Encouragement of underwater Building is provided by the glamorous view beneath the

Water of fishes, sea beds, different creatures and coral Reefs. This paper discuss about the
materials which Should be used for the construction of underwater Buildings, ways of
building and special requirements, the possibility of such constructions, advantages and
disadvantages of underwater buildings, the impact of Such buildings on environment,
effect on the social life and transportation.

1.2 Materials used for construction

There are many materials to be had for the building but our Selection should be such that
the material fulfils our requirement and to be had with a minimal price. Whilst choosing

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the materials to be used inside the manufacturing, it is critical to make sure that the
burden restriction is not exceeded. The principle fabric used for construction underwater
changed into a unique kind of steel and acrylic. The acrylic fabric is used specifically for
visibility, on the same time because the steel is used for reinforcements (enables).
Excessive energy steel is used as it is in particular Reasonably-priced, and has its
immoderate yield electricity. It isn’t always additionally a terrific conductor of power and
Warmth. It’s far an excessive corrosion resistance. Acrylic Fabric is used in preference to
glass; it is better than glass due To being much less dense, and it's also has higher effect
Electricity than the glass. Acrylic gives the herbal duration and colourings of the
encompassing materials than glass. It’s Also proper insulator of strength which is good in
searching out the fitness and safety of clients and underwater creatures.

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2. TECHNIQUE OF UNDERWATER CONSTRUCTION

As we all know any construction that is laid in water comes under underwater
construction, it may be a tunnel, a bridge, dams or some other. As we think of a
construction, concrete, foundations, construction technology etc., are some of the aspects
that come to our mind. So for underwater constructions, before considering concrete
mixtures to be used our main problem is how to lay foundations in water? As digging,
laying piles as foundations is a bit difficult task.

For this, there are certain methods that are being followed by the engineers of these days.
To lay foundations, at first we need to isolate water from the site. This is done by caissons
and cofferdams. These caissons and cofferdams can be considered as water retaining
boxes or these can also be called as watertight boxes.

Once these watertight boxes are built at the construction site in water, these boxes are
now dewatered by using suction pipes or some other equipment and that creates some dry
space to work on. Later chiselling, drilling and boring are carried out until a hard rock
surface is found or reached. And thus foundations are laid as a base for pillars. These
boxes are made by using sheet piles that overlock each other to form a watertight box

2.1 Cofferdam

A cofferdam, also called a coffer, is an enclosure built within, or in pairs across, a body
of water to allow the enclosed area to be pumped out. This pumping creates a dry
working environment so that the work can be carried out safely. Enclosed coffers are
commonly used for construction or repair of permanent dams, oil platforms, bridge piers,
etc., built within or over water.

These cofferdams are usually welded steel structures, with components consisting
of sheet piles, wales, and cross braces. Such structures are usually dismantled after the

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construction work is completed.

Fig 2.1: Cofferdam

2.1.1 Cofferdam Types

Most common cofferdam types are:

(1) Single wall cofferdams

As the name indicates, single wall cofferdams have only one wall. Typically, single wall
cofferdams are built using sheet piles.

•Single wall cofferdams can be built quickly with less cost.

•Dewatering and constant repairs are needed for single wall cofferdams.

•The cost is less for single wall cofferdams.

(2) Double wall

Double wall cofferdams are somewhat permanent in nature and are built to last for few
years. When construction work can take many years, single wall cofferdams may not be
suitable. Single wall cofferdams leaks and dewatering is required on a regular basis. This
problem can be avoided with a double wall cofferdam.

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•Double wall cofferdams are costly and need less maintenance. In addition, dewatering
inside the work site is negligible.

(3) Cellular wall

Cellular cofferdams are built when large areas need to be kept dry. Cellular structures can
stand-alone and need not be braced.

(5) Earth type

It is the simplest type of cofferdam. It consists of an earth bank with a clay core or
vertical sheet piling enclosing the excavation. It is used for low-level waters with low
velocity and easily scoured by water rising over the top.

(6) Timber crib

Constructed on land and floated into place. Lower portion of each cell is matched with
contour of river bed. It uses rock ballast and soil to decrease seepage and sink into place,
also known as “Gravity Dam”. It usually consists of 12’x12’ cells and is used in rapid
currents or on Rocky River beds. It must be properly designed to resist lateral forces such
as tipping / overturning and sliding.

(7) Rock fill.

These dams are very pervious, to prevent water from seeping an impervious membrane of
soil is provided in the dam. The height of the dam is can be up to 3m. The slope can be
maintained at 1:1.5 to 1:125. The slope on the water side is pitched so as to protect dam
from wave action.

2.1.2 Cofferdam components:

• Sheet piling: Sheet piling is a manufactured construction product with a mechanical

connection “interlock” at both ends of the section. These mechanical connections
interlock with one another to form a continuous wall of sheeting. Sheet pile applications
are typically designed to create a rigid barrier for earth and water, while resisting the
lateral pressures of those bending forces. The shape or geometry of a section lends to the
structural strength. In addition, the soil in which the section is driven has numerous
mechanical properties that can affect the performance.

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• Bracing frame

• Concrete seal: The typical cofferdam, such as a bridge pier, consists of sheet piles set
around a bracing frame and driven into the soil sufficiently far to develop vertical and
lateral support and to cut off the flow of soil and, in some cases the flow of water (Fig
The structure inside may be founded directly on rock or firm soil or may require pile
foundations. In the latter case, these generally extend well below the cofferdam. Inside
excavation is usually done using clam shell buckets. In order to dewater the cofferdam,
the bottom must be stable and able to resist hydrostatic uplift. Placement of an underwater
concrete seal course is the fastest and most common method. An underwater concrete seal
course may then be placed prior to dewatering in order to seal off the water, resist its
pressure, and also to act as a slab to brace against the inward movement of the sheet piles
in order to mobilize their resistance to uplift under the hydrostatic pressure (Fig. 5)

Fig 4 – Typical cofferdam (with seal)

2.1.3 Advantages of Cofferdam

Performing work over water has always been more difficult and costly than performing
the same work on land. And when the work is performed below water, the difficulties and
cost difference can increase geometrically with the depth at which the work is performed.
The key to performing marine construction work efficiently is to minimize work over
water, and perform as much of the work as possible on land. Below some of the
advantages of cofferdams are listed

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 Allow excavation and construction of structures in otherwise poor environment

 Provides safe environment to work
 Contractors typically have design responsibility
 Steel sheet piles are easily installed and removed
 Materials can typically be reused on other projects

2.2 Caisson
Caisson is a watertight retaining structure used, for example, to work on the foundations
of a bridge pier, for the construction of a concrete dam, or for the repair of ships. Caissons
are constructed in such a way that the water can be pumped out, keeping the work
environment dry.

Fig 5: caisson in china

2.2.1 Types

To install a caisson in place, it is brought down through soft mud until a suitable
foundation material is encountered. While bedrock is preferred, a stable, hard mud is
sometimes used when bedrock is too deep. The four main types of caisson are box
caisson, open caisson, pneumatic caisson and monolithic caisson.

1. Box

A box caisson is a prefabricated concrete box (with sides and a bottom); it is set down on
prepared bases. Once in place, it is filled with concrete to become part of the permanent
works, such as the foundation for a bridge pier. Hollow concrete structures are usually

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less dense than water so a box caisson must be ballasted or anchored to keep it from
floating until it can be filled with concrete. Sometimes elaborate anchoring systems may
be required, such as in tidal zones. Adjustable anchoring systems combined with a GPS
survey enable engineers to position a box caisson with pinpoint accuracy. Citation needed

2. Open

An open caisson is similar to a box caisson, except that it does not have a bottom face. It
is suitable for use in soft clays (e.g. in some river-beds), but not for where there may be
large obstructions in the ground. An open caisson that is used in soft grounds or high
water tables, where open trench excavations are impractical, can also be used to install
deep manholes, pump stations and reception/launch pits for micro tunnelling, pipe jacking
and other operations. A caisson is sunk by self-weight, concrete or water ballast placed on
top, or by hydraulic jacks. The leading edge (or cutting shoe) of the caisson is sloped out
at a sharp angle to aid sinking in a vertical manner; it is usually made of steel. The shoe is
generally wider than the caisson to reduce friction, and the leading edge may be supplied
with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling
depressions and voids. An open caisson may fill with water during sinking. The material
is excavated by clamshell excavator bucket on crane.

3. Monolithic

A monolithic caisson (or simply a monolith) is larger than the other types of caisson, but
similar to open caissons. Such caissons are often found in quay walls, where resistance to
impact from ships is required.

4. Pneumatic

Shallow caissons may be open to the air, whereas pneumatic caissons (sometimes called
pressurized caissons), which penetrate soft mud, are bottomless boxes sealed at the top
and filled with compressed air to keep water and mud out at depth. An airlock allows
access to the chamber. A pneumatic (compressed-air) caisson has the advantage of
providing dry working conditions, which is better for placing concrete. It is also well
suited for foundations for which other methods might cause settlement of adjacent
structures.

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Construction workers who leave the pressurized environment of the caisson must
decompress at a rate that allows symptom-free release of inert gases dissolved in the body
tissues if they are to avoid decompression sickness, a condition first identified in caisson
workers, and originally named "caisson disease" in recognition of the occupational
hazard. Construction of the Brooklyn Bridge, which was built with the help of pressurised
caissons, resulted in numerous workers being either killed or permanently injured by
caisson disease during its construction. Barotrauma of the ears, sinus cavities and lungs
and dysbarism osteonecrosis are other risks.

2.2.2 Mechanism of caisson

Caisson is a box but with no floor underneath it. So, when we put it underwater instead of
filling up with water as it is airtight, bubbles form. So as a result, we have a dirt floor
from where all the water is kept out. But water is heavy so the surface of the water is
exerting pressure on the caisson and tries to enter the caisson. So, in order to solve this,
we build a platform up in the top and a tube connecting the caisson to the platform that
exerts compressed pressure into the surface of the caissons. The front pressure and the
chamber pressure equalizes, therefore. The workers climb down in the box and they start
digging the dirt out of it. Now if the dirt is taken out manually, all the water will come
inside and drown everything. To solve this, we build a pipe full of water. Air pressure
from the environment and inside pressure of the caisson keep the water intact in the pipe.
Next, the workers send a bucket through the pipe and fill it with dirt and then carried back
up. Thus, the workers can dig their way down the riverbed.

2.2.3 Components of Pneumatic Caissons

Following are the various components of pneumatic caissons:
Air Shaft: A passage connecting in between the working chamber and air lock is termed
as 'air shaft' This passage or air shaft is used by the workmen or workers to reach to the
working chamber to ground surface. If caisson is too large in size, the separate unit of air
shaft may be provided for workers and material. Air Shaft is made up of steel material.
The joint involved in air shaft are sealed by rubber gasket air lock is provided on each air
shaft at top. When sinking process is going on, air shaft is extended above the water level.

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Working Chamber: Working Chamber height is about 3 m and is totally air tight and
made up of structural steel. To prevent the entry of air and water into the chamber, the air
inside the chamber is kept at a pressure just more than atmosphere pressure. External
surface of chamber is kept thick. Chamber is leak proof and smooth to reduce skin
friction. To facilitate the proper processing of sinking, a cutting edge is provided at the
bottom.

Air Lock: A chamber made of steel provided at the upper end of the air shaft above the
water level is called as 'Air Lock'. Air lock allows the worker or workmen to enter or exit
from the caisson without releasing the air pressure in the working chamber.

• The air locks have two air tight doors, one door opens into shaft and another door opens
to the atmosphere. When workmen enter the airlocks through the outside door, then
pressure in the chamber is kept at atmospheric level. Pressure is increased gradually till it
becomes equal to the working chamber. Under these condition workmen is allowed to go
into the air shaft. Complete procedure is again done when workmen comes out of the air
shaft to air lock.

• By opening a valve in the airlock, fresh air is circulated in the shaft workers or workmen
are allowed to work into the working chamber up to 2 hrs.

• The maximum limit of working into the chamber is 2 hrs. Miscellaneous Equipment

Different types of miscellaneous equipment used:

1. Pumps
2. Motors
3. Air Compressors
These equipment are normally placed above the bed level.

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Fig 5: components of a pneumatic caisson

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3. COMPARISON OF CAISSONS AND COFFERDAM

Fig 6: caisson and cofferdam

Caissons and cofferdams are selected depending on site conditions. Caissons are
permanent structure used for small area where the water height is more than 12m
whereas cofferdams are temporary structures which are used for large area with water
height up to 12m.

A caisson is retaining water tight structure used to work for the construction of a
concrete dam, on the foundation of a bridge pier or for the repair of ships. They are sunk
through water during the process of excavation of foundation to exclude water which
eventually becomes an essential part of the substructure .
Cofferdams are temporary watertight enclosure pumped dry below the water line to
execute the building operation to be performed on dry surface.

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4. TYPES OF IMPOSED LOADS

A typical cofferdam will experience several loading conditions as it is being build and
during the various construction stages. The significant forces are hydrostatic pressure,
forces due to soil loads, water current forces, wave forces, ice forces, seismic loads and
accidental loads. In order to overcome the displaced water buoyancy, the tremie seal
thickness is about equal to the dewatered depth.

1. Hydrostatic pressure

The maximum probable height outside the cofferdam during construction and the water
height inside the cofferdam during various stages of construction need to be considered.

2. Forces due to Soil Loads

The soils impose forces, both locally on the wall of the cofferdam and globally upon the
structure as a whole. These forces are additive to the hydrostatic forces. Local forces are
a major component of the lateral force on sheet-pile walls, causing bending in the sheets,
bending in the wales, and axial compression in the struts

3. Current Forces on Structure

With a typical cofferdam, the current force consists not only the force acting on the
normal projection of the cofferdam but also on the drag force acting along the sides.
With flat sheet piles, the latter may be relatively small, whereas with z-piles it may be
substantial, since the current will be forming eddies behind each indentation of profile,

4. Wave forces

Waves acting on a cofferdam are usually the result of local winds acting over a
restricted fetch and hence are of short wavelength and limited to height. However, in
some cases the cofferdam should have at least three feet of freeboard or higher above the
design high water elevation than the maximum expected wave height. Wave forces will
be significant factor in large bays and lakes where the fetch is several miles. Passing
boats and ships, especially in a restricted waterway, can also produce waves. The force
generated by waves is asymmetrical and must be carried to the ground through the sheet

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piling in shear and bending. The water system must be designed to transmit the wave
forces to the sheet piles.

5. Ice forces

These are of two types: the force exerted by the expansion of a closed-in solidly frozen-
over area of water surface (static ice force) and the forces exerted by the moving ice on
breakup (dynamic ice force). As an example, for static ice force, a value of 4000 lb/ft2
has been used on cofferdams and structures on the great Lakes, whereas the value due to
dynamic ice force on a cofferdam-type structure are often taken at 12,000 to 14,000
lb/ft2 of contact area.

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5. METHOD OF CONCRETING

There are several methods to carry out underwater concreting such as tremie method,
pumping methods, preplaced aggregate concrete etc. which are described.

The underwater concreting techniques designed mostly to prevent cement washout.

These methods did not obtain the full purpose of avoiding cement wash out at early
stages of using under water concreting apart from cases where large masses of
concreting were employed.

However, more recent techniques could obtain the objective of preventing washing out
of concrete. In this article, various methods will be explored.

Methods of Underwater Concreting

Following are the methods of underwater concreting:

1. Tremie method

2. Pumping technique

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3. Hydro valve method

4. Pneumatic valve method

5. Skip method

6. Tilting pallet barge method

7. Preplaced aggregate concrete

8. Toggle bags method

9. Bagged concrete method

1. Tremie Method of Underwater Concreting

Fig 8: Typical Arrangement of Tremie Method of Underwater Concreting

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Underwater concreting using tremie method is convenient for pouring large amount of
high flow able concrete. The concrete is moved to the hopper by either pumping, belt
conveyer or skips.

Tremie pipe, which upper end connected to a hopper and lower end continuously
submerged in fresh concrete, is used to place concrete at the exact location from a
hopper at the surface. The reason to immerse the tremie pipe lower end is to prevent
intermixing of both concrete and water. Tremie pipe typical arrangement is shown in
Figure-8.

Process of Underwater Concreting using Tremie Method

There number of factors that should be considered during Tremie pipe technique of
underwater concreting:

Tremie Equipment

The tremie pipe might be configured in three different ways such as constant length that
is raised during concreting, pipe with different sections which dismantled during
concreting and telescope pipe.

An aluminium alloy pipe can adversely affect the concrete due to chemical reactions
between them therefore it should be avoided. The pipe should have an adequate diameter
to prevent blockage because of aggregate size.

The usual diameter is between 200- 300 mm and occasionally 150 mm and 450 mm
could be used but aggregate size should be considered for example 19 mm and 40 mm
aggregate size is lower limit for 150 mm 200 mm pipe diameter respectively.

Tremie seal

To avoid intermixing water and concrete in the pipe, a wooden plug of plat is used to
seal the end of the pipe. This prevents entering water in to the pipe and keeps it dry.

After the pipe reach the intended position the concrete is poured and break the seal. Then
concrete flow out of the pipe and creating a seal by accumulating around the lower end
of the pipe

Placing the concrete

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As soon as concreting began the pipe mouth should be submerged up to 1- 1.5 m into
fresh concrete to prevent water entering the pipe. The concrete flow rate is controlled by
lowering and raising the pipe and either decrease or increase in concrete discharge
indicates the loss of the seal, therefore flow of concrete should be continuous and
carefully monitored.

Flow pattern

Two types of flow pattern are recognized namely, layered and bulging. The bulging flow
is desired because it displaced the concrete uniformly which leads to lesser laitance
deformation and flatter slopes.

2. Underwater Concreting using Pumping Technique

Fig 9: Typical Configuration of Underwater Concreting Pump Line

Underwater concreting using pumping technique is a developed version of Tremie pipe

and it is quicker method for concreting in areas that is difficult to access such as under
piers.

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Pumping provide several advantages that Tremie pipe is lacking for example, pouring
concrete from mixer to formworks directly, solve blockages in the pipe because
concreting is through pumping instead of using gravitational force, and risk of
segregation is decreased. Figure 9 show typical pipeline configuration.

3. Hydro Valve Method of Underwater Concreting

This method of underwater concreting is developed and employed by the Dutch in 1969.
A flexible hose which hydrostatically compressed is employed to pour concrete.

As soon as concrete placed in the upper of the pipe, both friction inside the pipe and
hydrostatic pressure is overcame by concrete weight. This leads to move concrete slowly
in the pipe and avoid segregation. A rigid tubular section is used to seal the end of the
hose. This method is not costly and quite simple. Figure 3 shows typical hydro valve
arrangement.

Fig 10: Hydro Valve Apparatus for Underwater Concreting

4. Underwater Concreting using Pneumatic Valves

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Pneumatic valves are joined to the end of the pipe line of concrete. There are different
types of valves which are employed for underwater concreting such as Abetong-Sabema
and Shimizu. These two valves are alike apart from a sensor that attached to the latter; its
function is to close the valve when concrete reach determined thickness.

Another type of valve is available which can be used to pour concrete at a depth of 52m
without immersing end of the pipe. The function of the valves is to permit, restrict, stop
the discharge of concrete and this method is the useful technique. Figure 11 show
Abetong-Sabema valve.

Fig 11: Abetong-Sabema Pneumatic Valve

5. Underwater concreting using the Skips Method

The equipment that is used for conveying concrete is a bucket with double door opening
at the bottom and overlapping canvas flaps which is fitted at the top to prevent concrete
washing. The skip is lowered down through water slowly as soon as it filled with
concrete and when it reaches the location the doors are opened either automatically or
manually.

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The Skip technique of underwater concreting is suitable for cases where a large mass of
concrete is required for stabilizing foundations and small amount of concrete is needed
for different locations. Shows opened and closed skips.

Fig 12: concreting by bucket method

6. Underwater Concreting using Tilting Pallet Barge

This technique is useful for shallow water and the concrete is poured in thin layers.
Along the deck of the barge a tilting pallet is constructed upon which concrete is spread
uniformly and then fell into the water freely.

7. Underwater Concreting using Preplaced Aggregate Concrete

Preplaced aggregate concrete method is quite good for cases where pouring ordinary
concrete is difficult or improbable. It includes placing aggregate in the forms then
injecting concrete into the bottom and filled the forms to the top.

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To prevent trapping water and air, concreting is beginning from the bottom. That is why
it is necessary to position the tubes in the forms before placing the aggregate.Concrete
strength about 70 to 100 percent of conventional concrete can be obtained in this
technique. The pipes are distributed with the maximum distance of 1.5 m and their
diameters ranges from 19 – 35 mm.

Fig 13: Preplaced Aggregate Concrete with Injecting Tubes

8. Toggle Bags Method

Toggle Bags method is useful when small amount of concrete is required. A reusable
canvas bag is sealed at the top with chain and secured with toggles is filled with concrete
and dropped carefully into the determined location then through opening at the bottom of
the bag the concrete is discharged.

9. Bagged Concrete Method

Bagged concrete method used for renew ballast or to seal holes temporarily. The bags
are produced from considerably strong fabric with capacity of 10 -20 liters and it carried
by divers to the selected position. The concrete slump is between 19- 50 mm and 40 mm
is the maximum aggregate size that can be used. The installation of the bags is similar to

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bricks in order to create bonds.

Fig 14: bags stacked one over other in bag concreting method

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6. UNDERWATER CONCRETE PROPERTIES

1. Thermal behaviour
One of the most critical problems with mass concrete is the thermal stress caused by heat
of hydration. The problem is especially pronounced for in-the wet construction of
navigation structures, since the thermal expansion of mass concrete can lead to
unacceptable cracks in the precast concrete form. The problem is exacerbated by the fact
that underwater concrete usually has to be continuously placed without construction
joints, giving little time for heat dissipation.
Conventional underwater concrete mixtures generally are not suitable for mass concrete
construction due to their high cement content. Common means to control thermal stress
include:

A. Use a large proportion of pozzolans or GGBF slag as replacement of Portland cement.

B. Lower the concrete placement temperatures to slow down early cement hydration and
lower the peak temperature rise of the concrete mass.

C. Plan concrete placement sequences to minimize temperature gradients within the

concrete mass.

D. Use insulating covers to control temperature gradients within concrete mass.

E. Design the precast concrete forms in such a way as to minimize thermal cracking

2. Laitance, bleeding, and segregation

laitance is "a layer of weak and nondurable Material containing cement and fines from
aggregates, brought by bleeding Water to the top of over wet concrete. In underwater
concrete, laitance is mainly a result of the washing out of cementitious materials by
water as well as Bleeding and segregation of concrete.
In "in-the-wet" construction of navigation structures, however, the laitance And bleeding
are detrimental if underwater concrete has to be placed beneath an Overhanging precast
concrete slab so as to bond to the slab. As laitance and Bleed water flow to the top
surface of the mass concrete, a weak layer of Concrete or possibly a gap will likely
develop between the slab and the Underwater concrete, resulting in a loss of structural

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integrity. Thus, vent Holes and/or collection sumps should be provided to remove
laitance wherever is possible. The formation of laitance should be kept to a minimum as
discussed below.
To minimize laitance formation, the construction operation should cause as little
disturbance to the concrete underwater as possible. Most of the Disturbance occurs
during starting and restarting of the placement, or result from loss of the seal or dragging
the tremie horizontally while embedded in the Concrete underwater. Therefore, the
tremie mouth should be always embedded in the fresh concrete and, to the extent
possible, the embedment depth should Be moderately deep (0.7 m (2 ft) minimum).
Vertical movement of the tremie pipe or pump line should be limited To that absolutely
necessary. Horizontal movement of embedded tremie or Pumpline should be generally
prohibited in mass underwater placement
In developing proper concrete mixtures to reduce bleeding, a number of Approaches can
be taken in the trial batching stage. In general, the bleeding Rate and bleeding capacity
can be reduced by a combination of several Approaches as listed below:

 Use of silica fume and fly ash as a replacement of Portland cement.

 Use of low water-to-cementitious material ratios, preferably less than 0.45.
 Increased proportions of fine aggregates, especially the particles smaller than 70
pm.
 Adjustment of retarding admixture to reduce bleeding while keeping adequate
slump retention

3. Form pressure

Underwater concrete has been historically used for tremie seal of Cofferdams where
lateral form pressure is not a serious concern. In the past, only a limited number of
underwater construction projects required Consideration of the hydrostatic pressure of
fresh concrete on formwork. For In-the-wet construction of navigation structures,
accurate evaluation of the form Pressure is critical. The construction method utilizes
precast concrete segments as the in situ form for underwater concrete. As the concrete is
being placed into the form, the hydrostatic pressures of the concrete on the form increase
proportionally. Past experience shows that the form pressures in combination with the
thermal expansion of the concrete often dictate the design of the precast form.

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In principle, the form pressures decrease when the fresh concrete gradually transforms
from a liquid state into a plastic state. If placement of concrete is Slow enough to allow
the concrete at the bottom to stiffen, the form pressure at the location will
correspondingly decrease. Past experience shows that neglecting the time-dependent
reduction of the form pressures often leads to over conservative and uneconomical
design of the precast form

4. Strength and the other properties of hardened concrete

The strength of underwater concrete has been extensively studied in the Past. The past
studies concluded that fully immersed concrete has excellent Curing conditions. If good
placement procedures are followed, the long-term Strength of underwater concrete
should be higher than that of concrete placed in the dry.

For example, a series of early tests conducted by the U.S. Bureau Of Reclamation
(Bureau of Reclamation 1975) showed that, in a period of 6 months, continuously
immersed concrete developed an average compressive Strength about 25 percent higher
than that of comparable concrete with only 7 days moist curing The increase in strength
at later age is especially pronounced in concrete Containing mineral additives.

Concrete containing fly ash and/or slag usually Develops higher strength than Portland
cement concrete beyond 90 days Concrete strength appears to be influenced by the
placement method.

Coring and testing of large-scale underwater concrete placements indicated that Tremie-
placed concrete tends to have higher strength than pump-placed or Hydro valve-placed
concrete (Netherlands Committee for Concrete Research 1973). It has been found that
the concrete placed by direct pumping or the Hydro valve method is usually less
cohesive and contains more voids, probably Due to the method and the rate of concrete
discharge from the end of the pipe.

The tensile strength of concrete develops more slowly than the compressive Strength
with the curing age. An approximate 10-percent increase in the tensile strength of
underwater concrete is expected over that of air-dried concrete.

The shear strength is expected to show an increase similar to that of the tensile
Strength. However, the bond strength between the precast concrete form and

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underwater concrete may vary to a greater extent, depending on such factors as Surface
preparation of the precast concrete and the underwater concrete Placement technique to
remove bleeding water and laitance.

If full-strength bonding between precast concrete and tremie concrete is required in

certain Critical areas, it is recommended that additional measures be taken. Common
Strengthening measures include use of steel studs, surface roughening, and Corrugated
precast concrete forms to enhance the mechanical locking.

Algae growth (slime) should either be inhibited or cleaned off. Fortunately, the growth
of algae depends on light. Since many of in-the-wet schemes proposed block off light
inside the precast forms, algae growth will be Minimum. However, the possibility of
rapid mussel growth (e.g., zebra Mussels) must not be discounted.

The elastic modulus of concrete is not influenced in the same way by the Environment.
In the first 3 months to 1 year, the elastic modulus of concrete Increases at a higher rate
than the compressive strength and remains almost Constant at later ages. The elastic
modulus in an immersed condition is about 15 percent greater than that of concrete in an
air-dried condition.

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7. CHALLENGES

1. Budget

Building beneath water is a very costly way because of using heavy machinery, devices
and professional Employees. Building below water also includes some of Welfare and it
desires to large price range.

2. Erosion

Erosion is the method of weathering and delivery of Solids (sediment, soil, rock and
different rock particles) in the natural surroundings or their source and deposits them
someplace else. It normally takes place because of Transport with the resource of wind,
water, or ice so Engineers ought to pick out appropriate materials for beneath water
building.

3. Location of fuel

Any coincidence may also be possible when the driller Machines and other machinery
are trying to find out oil Or to any ship also can damage the outlook and structure Of the
building it's far out of manage.

4. The hassle of warmth of the water

The temperature varies reasonably over the surface of Water, it is heated from the
ground from the below by the Usage of daylight hours, but at depth maximum of the
Water may be very cold.

5. The problem of pressure

Stress performs a large characteristic in persuading the Guidelines of the constructing

additionally people comes to problems one or the other at some stage in the
Development system or at some point of the protection Procedure.

6. Environmental building elements

No doubt that the primary problem that is to be had in our mind is the problem of
Aeration. There need to be a supply of renewable air that Helps in respiratory, and

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removing unwanted gases. Permits discover a solution, for the air flow hassle, that
Changed into implemented at the same time as the Development of the underwater
Holland tunnel. Tunnels in particular, have an exceptional trouble with ventilation due to
gases produced thru trains and cars.

This hassle Modified into addressed with the aid of Clifford Holland, The tunnel's
clothier. His intention was to find ways to Easy exhaust fumes and pump in clean air,
reaching this with the aid of manner of the usage of aeration towers, and enthusiasts to
transport air in and out. In the end, air can be transformed each ninety seconds.

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8. CONCLUSION

This record analysed a present day generation of construction of structures beneath the
water. Constructing building under the water is the future establishment that has a superb
effect on the environment. This document has shown up what underwater buildings are.
It has mentioned the impact of underwater constructions on environment and social
Existence. It has tested the materials which can be utilized in underwater constructing. It
additionally has described the Problems that are faced during the construction of
structures below the water. It has described the air flow structures which are used. It has
higher the reader with a few examples of underwater constructions that have been built
or under Manufacturing, in order to mesmerize him with the appealing View and the
magnificence of buildings. So this document acclaims the reader to don't forget this
technology of Building, and convince him to stay down there.

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9. REFERENCES

1. Yiqiang Xiang, Ying yang “challenge in design and construction of submerged

floating tunnel and state-of-art”,2016

2. Zaran D. Patel, Dr. Jayeshkumar Pitroda “a study on the developing concepts of

underwater construction”,2017

3. Sam X. Yao, Dale E. Berner, Ben C. Gerwick, Ben C. Gerwick, “Assessment of

Underwater Concrete Technologies for In-the-Wet Construction of Navigation
Structures”, 2001

4. Gopal Murty, Bhumka Das, Kumar Umang “a case study on underwater

construction”, 2018

5. Kmaran M. Nemati “temporary stuctures- cofferdam”, 2005

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