CAISSON FOUNDATION

INTRODUCTION

The term caisson has been derived from the French word ‘CAISSEE’, meaning BOX.

It can be round or rectangle in plan.

It is commonly used where foundation under water is done.

It can sunk from surface of either land or water to the desired depth.

TYPES OF CAISSON

Open caisson

Box caisson

Pneumatic caisson

OPEN CAISSON

Also called as well caisson.

They are open at both the ends.

These are boxes of timber, steel or R.C or masonry.

Small caisson consists of one opening or well, while larger one contain a series of wells.

PROCEDURE

The caisson is cast and flatted to the site and sunk.

When it reaches the required depth concrete is deposited through water to some depth.

After the concrete gets hardened, the water will be pumped out.

The caisson is finally filled completely with concrete.

BOX CAISSON

Also called as Floating caisson.

They are open at top and closed at bottom.

They can be made of steel, R.C or timber.

The caisson is built on land, then launched and brought to the site where they have to be sunk.

They are filled with concrete or stone masonry and sunk until it rests on the river bed, which has been prepared to receive it, or on a pile cluster to form a lower part of a bridge pier.

PROCEDURE

TOWING OF CAISSON

APPLICATIONS OF BOX CAISSON

Bearing stratum is available at shallow depth

Loads are not heavy

For wharfs and break waters

PNEUMATIC CAISSON

“Pneumatic" means "with air" “Caisson" means "a box“

The pneumatic caisson method works on the same principle as a cup pressed into some water upside down

EXECUTION OF THE PNEUMATIC CAISSON

1.Preparation of the ground for installation

We level surface of working site where the caisson

is to be installed and improve the surface conditions

so that appropriate supporting force can be supplied.

2.Construction of working chamber

We construct a working chamber at a bottom of

the caisson, in which earth is excavated and removed.

The chamber is pressurized to the same pressure as

the ground water pressure to make it watertight

EXECUTION OF THE PNEUMATIC CAISSON

3. Rigging

Cylindrical steel shafts are used for workers to

enter or exit the pressurized working chamber and to

remove excavated earth.

4. Repeated excavation to sink & construct

caisson

We excavate and construct the caisson every 4m

height, and repeatedly sink it by excavating the

ground and constructing it to the desired depth.

EXECUTION OF THE PNEUMATIC CAISSON

5. Testing the bearing capacity of soil

After the caisson has sunk to the specified depth,

we test and confirm that if sufficient bearing

capacity of soil has been obtained.

6. After concrete filling for working

chamber

After confirming the bearing capacity, we remove

equipments in the working chamber and fill

concrete, which means completion of works.

1.PREPARATION OF THE GROUND FOR INSTALLATION

2.CONSTRUCTION OF WORKING CHAMBER

3.RIGGING

4a.REPEATED EXCAVATING TO SINK AND CONSTRUCT THE CAISSON

4b.REPEATED EXCAVATING TO SINK AND CONSTRUCT THE CAISSON

5.TESTING THE BEARING CAPACITY OF SOIL

6.AFTER CONCRETE FILLING FOR WORKING CHAMBER

APPLICATIONS

The Pneumatic Caisson Method is used for many different structures:

Foundations of road and railway bridges

Subway tunnels facilities

Basements and foundations buildings

Water supply and sewage facilities

Other facilities (e.g. garbage pits)