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

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 chamberWe 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. RiggingCylindrical steel shafts are used for workers to

enter or exit the pressurized working chamber and to remove excavated earth. These shafts have locks (for both men and materials) to regulate the difference between the atmospheric pressure on the ground and the pressure in the chamber. Installation of such locks and shafts is called "rigging work".

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 soilAfter 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 chamberAfter confirming the bearing capacity, we remove equipments in the working chamber and fill concrete, which means completion of works.

EXECUTION OF THE PNEUMATIC CAISSON

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)

FOUNDATIONS OF ROAD AND RAILWAY BRIDGES

BRIDGES CONSTRUCTED AT THE WATER DEPTH OF 50 TO 60 M.

SUBWAY TUNNELS FACILITIES

BASEMENT AND FOUNDATION BUILDINGS(Eg. UNDERGROUND PARKING ZONES)

WATER SUPPLY AND SEWAGE FACILITIES(Eg. TREATMENT PUMP BUILDING)

OTHER FACILITIES (E.G. GARBAGE PITS)

OTHER TYPES

There are few more methods in caisson foundation.

• Jacking caisson method

• Space System Caisson

JACKING CAISSON METHOD

Jacking caisson method is to sink large scale caisson thruster into ground by using jacks with rods connected to earth anchor.

Intake shaft of 14 meter ø. is thrusted in the ground at 50.7 meter below by using 12 jacks of 240 ton thrust force. The caisson itself is constructed on the ground by each rot of 5 meter.

Dimension of 26x19 meter is sunk by 8 jacks in the ground depth 18.5 meter, while inside of caisson is excavated by clam shell

JACKING CAISSON METHOD

SPACE SYSTEM CAISSON

• The gravel is filled between wall surface and ground, and the skin friction resistance is reduced.

• The SS caisson method gently and accurately install the caisson in non-loading.

• The problem of the conventional open caisson method is solved.

FEATURES OF THE SS CAISSON METHOD

• It is gently installed only at the dead weight at the good accuracy.

• Subsidence and collapse of the ground in the circumference are not caused.

• It is applicable for various geology.