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.

PROCEDURE 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.

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)