Notes on introduction and design of caissons

CEC NOTES FINAL
TOPIC-CAISSONS
A caisson is a watertight chamber that can be used for construction or diving operations. In
construction, it is used to create a dry work environment for construction of bridges, dams, and
other structures in water or mud. In diving, it is used to allow divers to work at great depths for
extended periods of time by providing a pressurized environment to counteract the water
pressure at depth.
Types of Caissons
Open caissons
Pneumatic caissons are watertight chambers that are used in construction to create a dry work
environment. They consist of a steel or concrete structure that is lowered into the water and then
filled with compressed air to create an air-tight seal. This allows construction workers to work
inside the caisson in a dry environment, even when it is submerged in water or mud.

Pneumatic caissons are typically used in the construction of bridges, dams, and other structures
in water or mud. They can also be used for the construction of foundations for buildings and
other structures. They are most commonly used in shallow waters and are typically not used at
depths greater than around 60 feet (18 meters)
Open caisson
An open caisson is a hollow structure with both an open top and bottom that is designed to keep water
out of a construction zone. It is one of three caisson shaft types, which also include pneumatic and box

caissons. Open caissons are used in trenchless operations, such as in the excavation of entrance or exit
pits.
BOX CAISSON
A box caisson is a type of pneumatic caisson that is used in construction to create a dry work
environment. It is a rectangular-shaped, watertight chamber that is made of steel or concrete. It is
lowered into the water and then filled with compressed air to create an air-tight seal. This allows
construction workers to work inside the caisson in a dry environment, even when it is submerged
in water or mud.
Box caissons are typically used in the construction of bridges, dams, and other structures in
water or mud. They can also be used for the construction of foundations for buildings and other
structures. They are most commonly used in shallow waters and are typically not used at depths
greater than around 60 feet (18 meters).
The process of using a box caisson involves excavating the soil around the caisson, lowering it
into place, and then filling it with compressed air to create the air-tight seal. Once the seal is
created, construction workers can enter the caisson and begin their work. After the work is
completed, the compressed air is released and the caisson is removed.

Defects in caissons
1.sand blowing
It occurs when wind-borne sand particles are blown onto the caisson, causing damage to equipment,
materials, and finished surfaces. This can be caused by a lack of barriers or windbreaks around the
construction site, or by winds that are particularly strong or blowing in the direction of the site.
2.sinking
Sinking of a caisson is a problem that can occur during the construction process. It occurs when
the caisson settles or sinks into the ground, causing the structure on top of it to become unstable.
This can be caused by a number of factors including:
• Poor soil conditions: If the soil is not strong enough to support the weight of the caisson
and the structure on top of it, the caisson may sink.
• Construction errors: If the caisson is not built or placed correctly, it may sink.
• Improper filling of caisson: if the caisson is not filled with concrete completely or not
placed level, it may sink.
• Groundwater infiltration: If water enters the caisson, it can cause the soil around the
caisson to become saturated, leading to sinking.
Topic-COFFERDAM
A cofferdam is a temporary structure used to dry an area of a body of water in order to allow
construction or repair work to be done on a bridge, dam, or other structure that is typically underwater.
It is typically made of steel or concrete and is used to create a dry work area by diverting the flow of
water around the area. Cofferdams are often used in the construction of bridge and dam foundations, as
well as for the repair and maintenance of existing structures.

TYPES OF COFFERDAMS
1. GRAVITY COFFERDAM
A gravity cofferdam is a type of cofferdam that relies on its own weight to maintain its stability
and keep water out of the construction area. It is typically made of steel or concrete and is
designed to be self-supporting, with no need for additional bracing or support.
Gravity cofferdams are built in sections, with each section being placed and filled with material
such as soil or rock to add weight and stability. The sections are then joined together to form a
continuous barrier around the construction area.
One of the main advantages of using a gravity cofferdam is that they can be built quickly, and
they are relatively easy to construct. However, they can only be used in certain conditions, such
as in shallow water and where the surrounding soil is stable and can support the weight of the
cofferdam.
METHODS OF CONSTRUCTING GRAVITY COFFERDAMS
There are several methods for constructing gravity cofferdams, including:
1. Excavation Method: This method involves excavating the soil inside the cofferdam to
create a dry work area. The excavated soil is then used to backfill and support the
cofferdam walls.
2. Fill and Compaction Method: This method involves filling the cofferdam area with
material such as soil or rock and compacting it to create a solid foundation for the
cofferdam walls.
3. Prefabricated Unit Method: This method involves constructing the cofferdam walls using
precast concrete or steel sections that are assembled on site. This method is faster than
traditional construction methods and can be used in areas with limited access.

4. Combination Method: This method combines the use of excavation, fill and compaction
and prefabricated units to construct the cofferdam.
5. Sheet Pile Method: This method involves driving sheet piles into the ground to form the
cofferdam walls. The sheet piles are then filled with material such as soil or rock to add
weight and stability.
The method chosen depends on the site conditions, cost, and time available for the construction.
2. SHEET PILE COFFERDAM
A sheet pile cofferdam is a type of cofferdam that uses interlocking sheets of steel, wood, or
other materials to form a barrier and keep water out of the construction area. Sheet piles are
driven into the ground, usually by a pile driver, to create a continuous wall that can withstand the
water pressure and keep the construction area dry.
Sheet pile cofferdams are commonly used in deep water or where the soil is not stable enough to
support a gravity cofferdam. They can also be used in situations where the water level fluctuates,
such as in a tidal area, as the sheet piles can be adjusted to accommodate changes in water level.
Sheet pile cofferdams can be constructed relatively quickly and are relatively easy to install, but
they can be more expensive than other types of cofferdams. They also require regular
maintenance to ensure that they remain in good condition and can withstand the pressure of the
water.

METHODS OF CONSTRUCTING SHEET PILES COFFERDAMS
There are several methods used to construct sheet pile cofferdams, including:
1. Drive-in method: This method involves driving the sheet piles into the ground using a
pile driver. The piles are driven in a pre-determined pattern, and the gaps between the
piles are filled with soil or rock to add stability. This method is typically used in soil or
rock that is not too hard or dense.
2. Vibratory method: This method involves using a vibratory hammer to drive the sheet
piles into the ground. The hammer vibrates the pile, which helps to loosen the soil and
make it easier to drive the piles in. This method is typically used in soil or rock that is
harder or denser than the soil that can be driven by the drive-in method.
3. Impact method: This method involves using an impact hammer to drive the sheet piles
into the ground. The hammer delivers a series of high-energy blows to the pile, which
helps to loosen the soil and make it easier to drive the piles in. This method is typically
used in soil or rock that is harder or denser than the soil that can be driven by the
vibratory method.
4. Float-in method: This method involves floating the sheet piles into place, and then
driving them into the ground. This method is typically used in deep water or in areas
where it is not possible to use a pile driver.
The method chosen will depend on the soil conditions, water depth and the accessibility of the
site and the budget.
3. ARCH COFFERDAM
An arch cofferdam is a type of cofferdam that uses a series of arches to create a barrier and keep
water out of the construction area. It is typically made of steel or concrete and is designed to be
self-supporting, with no need for additional bracing or support.
Arch cofferdams are built in sections, with each arch being placed and filled with material such
as soil or rock to add weight and stability. The arches are then joined together to form a
continuous barrier around the construction area.
Arch cofferdams are typically used in situations where the water level fluctuates, such as in a
tidal area, as the arches can be adjusted to accommodate changes in water level. They can also be
used in deep water and where the soil is not stable enough to support a gravity cofferdam.
Compared to other types of cofferdams, arch cofferdams are relatively easy to construct and
maintain, also they are more flexible than sheet piles cofferdams. However, they can be more
expensive than sheet piles cofferdams and they may need more space to be placed.

METHODS OF CONSTRUCTING ARCH COFFERDAMS
There are several methods of constructing an arch cofferdam, including the following:
1. Prefabricated arches: In this method, the arches are fabricated off-site and then
transported to the construction site for installation. This method can be faster and more
cost-effective, but it may be limited by the size of the arches that can be transported to the
site.
2. Cast-in-place arches: In this method, the arches are cast on-site using concrete. This
method can be more flexible, as the arches can be cast to any size or shape, but it may be
slower and more labor-intensive.
3. Combination of prefabricated and cast-in-place arches: This method uses a combination
of prefabricated and cast-in-place arches to create the cofferdam. This method can
provide the benefits of both methods, but it may be more complex and require more
coordination.
4. Arch-based Cofferdams: This method uses a combination of arches and sheet piles to
create the cofferdam. This method can provide the benefits of both arches and sheet piles,
but it may be more complex and require more coordination.
Maintenance of cofferdams
The maintenance of cofferdams is an important aspect of ensuring the safety and longevity of the
structure. Proper maintenance can help prevent leaks and failures, and prolong the lifespan of the
cofferdam. Some of the key maintenance tasks that should be performed on a regular basis
include:
1. Inspection: Regular inspections of the cofferdam should be conducted to check for any
signs of wear and tear or damage.
2. Leak detection: Check for leaks in the cofferdam and repair any that are found.
3. Water level monitoring: Monitor the water level in the cofferdam and make sure it is
within the safe range.
4. Drainage: Make sure that any drainage systems in the cofferdam are functioning properly
and that any standing water is removed quickly.
5. Maintenance of the supporting structure: Regularly check the supporting structure of the
cofferdam and repair or replace any damaged parts.
6. Cleaning: Remove any debris or sediment that may have accumulated in the cofferdam to
prevent blockages

TOPIC- DREDGING AND RECLAMATION
DEFINITIONS
DREDGING- is the process of removing sediment, debris, or other materials from the bottom of
a body of water. Dredging is typically done to maintain or deepen navigable waterways, to create
new land, or to extract minerals or other resources.
RECLAMATION- is the process of converting an area of land that has been disturbed or used
for a specific purpose, such as mining, into a more productive and sustainable land use. It
involves restoring the land to a condition that is suitable for the intended use, such as agriculture,
forestry, or development.
DREDGING PROCESSES
A.Pretreatment
Pretreatment in dredging refers to the process of preparing the dredged material before it is
disposed of or used for beneficial reuse. The goal of pretreatment is to remove any contaminants
or pollutants from the dredged material, so that it can be safely handled and used without causing
harm to the environment or human health.
There are several methods of pretreatment that can be used, depending on the characteristics of
the dredged material and the intended use of the material. Some common methods include:
1. Physical separation: Using screens or other equipment to separate the dredged material
into different size fractions, with the goal of removing any debris or large particles that
may contain contaminants.
2. Chemical treatment: Using chemicals to neutralize or remove pollutants from the dredged
material, such as acid neutralization or pH adjustment.
3. Biological treatment: Using microorganisms or other biological agents to break down
pollutants or contaminants in the dredged material.
4. Thermal treatment: Using heat to destroy pollutants or contaminants in the dredged
material, such as incineration or thermal desorption.
5. Water treatment: Using water treatment technologies to remove pollutants or
contaminants from the dredged material, such as flocculation, sedimentation, and
filtration.
Pretreatment is an important step in the dredging process, as it ensures that the dredged material
can be safely handled and used without causing harm to the environment or human health. It's
also important to comply with the regulations and standards established by the relevant
authorities.
B. Extraction

Extraction in dredging refers to the process of removing valuable materials or resources from the
dredged material. This can include minerals, such as sand, gravel, or clay, or other resources,
such as shells or peat.
There are several methods of extraction that can be used, depending on the characteristics of the
dredged material and the desired end product. Some common methods include:
1.Mechanical dredging: Using mechanical equipment, such as excavators or suction dredges, to
remove valuable materials from the dredged material. The most common types of mechanical
dredging equipment include:
a) Excavators: These are large machines that use a scoop or bucket to dig into the sediment
and remove it. They can be equipped with different types of buckets, such as clamshell
buckets or dredging buckets, depending on the type of material being dredged.
b) Trailing suction hopper dredgers (TSHDs): These are large vessels that use a dredging
pump and a suction pipe to suck up sediment and pump it into a hopper on the vessel.
The dredged material is then transported to a disposal site.
c) Cutter suction dredgers (CSDs): These are similar to TSHDs, but they use a cutter head to
break up and loosen the sediment before it is pumped into the hopper.
d) Backhoe dredgers: These are small dredgers that use a backhoe-like arm to dig into the
sediment and remove it. They are typically used for small-scale dredging projects.
e) Draglines: These are large machines that use a bucket or clamshell to dig into the
sediment and remove it. They are typically used for large-scale dredging projects.
2.Washing and screening: Using water and screens to separate the dredged material into different
size fractions, with the goal of removing the desired materials.
3.Classification: Using air or water to separate the dredged material based on density or particle
size, with the goal of removing the desired materials.
4.Magnetic separation: Using magnetic fields to remove ferromagnetic materials, such as iron,
from the dredged material.
5.Flotation: Using chemicals and air bubbles to separate the dredged material based on
buoyancy, with the goal of removing the desired materials.
C. TRANSPORTATION
Transportation of dredged material refers to the process of moving the dredged material from the
dredging site to a disposal or beneficial use area. The method of transportation will depend on
the type of dredged material, the distance to the disposal or beneficial use area, and the specific
project requirements. Some common methods of transportation include:
1. Pipelines: Dredged material can be pumped through pipelines to transport it to the
disposal or beneficial use area. This method is often used when the disposal or beneficial

use area is located a significant distance away from the dredging site or when the dredged
material needs to be transported through difficult terrain.
2. Barges or hopper dredgers: Dredged material can be transported by barge or hopper
dredger to the disposal or beneficial use area. This method is often used when the
disposal or beneficial use area is located in a body of water or when the dredged material
needs to be transported over a significant distance.
3. Trucks: Dredged material can be loaded into trucks and transported to the disposal or
beneficial use area. This method is often used when the disposal or beneficial use area is
located a relatively short distance away from the dredging site or when the dredged
material needs to be transported to an area that is not accessible by barge or pipeline.
4. Conveyor belts: Dredged material can be transported on conveyor belts to the disposal or
beneficial use area. This method is often used when the disposal or beneficial use area is
located a relatively short distance away from the dredging site or when the dredged
material needs to be transported to an area that is not accessible by other means.
D.DEPOSITION
Deposition of dredged material refers to the process of placing the dredged material in a
designated area after it has been removed from the dredging site. The method of deposition will
depend on the type of dredged material, the characteristics of the disposal or beneficial use area,
and the specific project requirements. Some common methods of deposition include:
1. Open water disposal: Dredged material can be placed in designated areas in the open
water such as designated dredged material disposal areas, deep ocean or in the sea bed,
away from sensitive habitats and shipping lanes. This method is often used when the
dredged material is not contaminated and can be safely placed in the open water without
causing significant environmental impacts.
2. Confined disposal facilities: Dredged material can be placed in confined disposal
facilities such as dredged material containment areas (DMCA) or engineered containment
facilities (ECF). This method is often used when the dredged material is contaminated
and needs to be contained to prevent the release of pollutants or when the dredged
material needs to be placed in a specific location for beneficial use.
3. On-land disposal: Dredged material can be placed on land in designated areas such as
upland or lowland disposal sites. This method is often used when the dredged material is
not contaminated and can be safely placed on land without causing significant
environmental impacts.
4. Beneficial use: Dredged material can be used beneficially in various ways such as
construction of coastal protection and beach nourishment, habitat creation and
restoration, land reclamation, and agricultural and industrial uses. This method is often
used when the dredged material is not contaminated and can be used beneficially without
causing significant environmental impacts.

METHODS OF DREDGING
A.BLASTING
Blasting method of dredging involves using explosives to break up and loosen sediment or
rock on the bottom of a body of water. The loosened material is then removed by dredging
equipment such as a suction dredge or a cutter dredge. This method is typically used in
deeper waters or in situations where the material to be removed is too hard to be dredged
using mechanical methods alone. It is also used to remove underwater obstacles or to create
channels or berths for boats and ships. However, the use of explosives can also have negative
environmental impacts, such as damage to marine life and habitats, and must be carefully
regulated and monitored.
B.CUTTING
Cutting method in dredging involves using a dredging equipment with a sharp cutting edge to
slice through and remove sediment or rock on the bottom of a body of water. This method is
typically used in shallow waters or in situations where the material to be removed is
relatively soft and can be cut easily. One of the most common cutting dredges is the cutter
suction dredge, which uses a rotating cutting head to break up and remove the material,
which is then pumped to the surface through a pipe. Another type of cutting dredge is the
chain ladder dredge, which uses a chain with cutting teeth to cut through the material and lift
it onto a conveyor belt. This method is often used for dredging channels, harbors and berths
for boats and ships
DREDGING PLANT
A.SPUDDED DREDGER
Spudded dredger is a type of dredging vessel that uses a spud, or a large vertical pole, to
anchor itself in place while it dredges. This allows the dredger to work in one spot and
prevent drift while it excavates sediment from the bottom of a body of water. Spudded
dredgers are typically used in shallow water and can be used for a variety of dredging
projects, including maintenance dredging, capital dredging, and environmental dredging.

B.TRAILER SUCTION DREDGER
A trailer suction dredger is a type of dredging equipment that is typically used for dredging and
excavation of materials from the bottom of bodies of water such as lakes, rivers, and harbors. It
uses a suction hose to suck up sediment, gravel, and other materials, which are then deposited in
a holding area or transported to a different location. The dredger is typically mounted on a trailer,
allowing it to be easily transported to different locations as needed. These dredgers are
commonly used for dredging channels, maintaining navigational channels, and removing
sediment from harbor

C. PONTOON DREDGER
A pontoon dredger is a type of dredging equipment that is typically used for dredging and
excavation of materials from the bottom of bodies of water such as lakes, rivers, and harbors.
It is a floating platform that supports a dredging pump, which is used to suck up sediment,
gravel, and other materials from the bottom of the water. The pontoon dredger is typically
powered by an on-board generator and is equipped with a discharge pipe that transports the
dredged materials to a designated location. These dredgers are commonly used for dredging
channels, maintaining navigational channels, and removing sediment from harbors. They also
can be equipped with excavator arm, crane and other tools for more versatile dredging
application

SKETCHING IN DREDGING
Sketching in dredging refers to the process of creating visual representations of a dredging
project, such as a map or cross-section, to help plan and communicate the details of the
project. These sketches can include information on the location of the dredging area, the
depth of the water, the type of material to be removed, and any potential obstacles or hazards
in the area. They may also include details on the equipment and methods to be used for the
dredging. Sketches are an important tool for dredging professionals as they help to ensure
that the project is executed safely and efficiently.
FACTORS AFFECTING CHOICE OF DREDGER
There are several factors that can affect the choice of dredger for a particular project, including:
1. Type of material to be dredged: Different dredgers are better suited for different types of
materials, such as sandy soils, clay, or rock.
2. Volume of material to be dredged: The volume of material to be dredged will determine
the size and capacity of the dredger required.
3. Depth of water: The depth of water in the dredging area will affect the type of dredger
that can be used, as some dredgers are not designed for deep water operations.
4. Accessibility of the dredging area: The accessibility of the dredging area, such as the
presence of obstacles or limited space, will affect the type of dredger that can be used.
5. Environmental considerations: The potential impact of the dredging on the environment,
such as on fish and other wildlife, will affect the type of dredger and dredging method
used.
6. Cost: The cost of the dredger, maintenance and operational cost is also an important
factor that is considered while choosing the dredger.
7. Dredging duration: The duration of dredging is also an important factor that is considered
while choosing the dredger.

8. Technical specification of dredger: Technical specification like dredging capacity,
dredging depth, speed of dredging, weight of dredger etc also plays an important role
while choosing the dredger.
RECLAMATION
Reclamation refers to the process of converting land that is not suitable for human use, such as
desert or marshland, into land that can be used for a specific purpose, such as agriculture or
urban development. This process typically involves a combination of techniques, including
irrigation, drainage, and the addition of soil or other materials. Reclamation projects can be large
in scale and may be undertaken by governments, corporations, or private individuals. They can
have both positive and negative impacts on the environment, economy, and communities
RECLAMATION METHODS
A.DYKE METHOD
Land reclamation by dyking, also known as dike building or dyke construction, is the process of
building a dike (or dam) to reclaim land from a body of water. This can be done for a variety of
purposes such as creating new land for agriculture or development, protecting against flooding,
or creating a new waterfront. The process typically involves excavating soil and rock from a
nearby area and using it to construct the dike, which is then typically planted with vegetation to
stabilize the structure and prevent erosion. The reclaimed land may need to be drained and
levelled before it can be used for development.

B.FILLING-IN ABOVE EXISTING WATER LEVEL
Land reclamation by filling in refers to the process of building up low-lying areas of land by
adding soil or other materials. This can be done for a variety of reasons, such as to create new
land for development, to expand existing land, or to protect against flooding. The materials used
for land reclamation can vary, and may include dredged materials, rock, or other types of fill.
Land reclamation can have both positive and negative impacts on the environment, such as
creating new habitats for wildlife, but also can lead to loss of wetlands, and destruction of natural
coastal habitats.

Notes on introduction and design of caissons

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Notes on introduction and design of caissons