Underwater construction is a method on how to place the concrete underwater.

Underwater construction is a method on how to place the concrete underwater.


It is opted when the foundation is most likely to lie underwater.

Construction in water poses many difficulties especially where the depth is considerable.

The main objective is to create dry and water free environment the stability of the structure is well
balanced

1. Underwater Construction 8 th Semester-2022

2. Introduction Underwater construction is a method on how to place the concrete underwater. It is opted when the foundation is most likely to lie underwater. Construction in water poses many difficulties especially where the depth is considerable. The main objective is to create dry and water free environment the stability of the structure is well balanced

3. Activities Includes: Power Generation Bridges Water Utilities

4. Ship Husbandry Industrial Mining

5. Underwater Construction techniques: There are two techniques : Caissons Cofferdams

6. Caissons 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. Permanent Structure Large Hollow structure that is sunk down through water. Used in Construction of bridge Piers, Building Columns, Dams. Following are the material used for the construction of caisson foundation. Wood Steel Reinforced Concrete

7. Caisson foundation is mostly used in deep foundation construction where the foundation should be extended up to or below the river bed so as to obtain the proper stability. Caisson foundation is one type of good foundation that is constructed in connection with piers and abutments in rivers and lakes, bridges, breakwater dock structures, and also in case of shore protection, lamp house, etc. Caisson foundation also used for pump house construction in which is subjected to huge vertical as well as horizontal forces. It is also occasionally used for large and multi-story buildings and other structures. Uses of Caisson Foundation :

8. Caissons Foundation

9. Types of caissons Open Caissons Box Caissons Suction Caissons Pneumatic Caissons

10. Open Caisson Foundation : An open caisson foundation is box types of construction that is generally open at the bottom and top of the box . These types of caisson are normally used for sandy soils or soft bearing stratum and where no firm bed is available at a higher depth. According to the shape of open caisson, they are also classified in further types: 1.Open Caisson Single Wall Open Caisson Cylindrical Open Caisson Open Caissons with dredging wells.

11. Construction of Open Caissons: The sinking process can be done in following conditions: Dry Water Bed. Dewatered Construction 3.Artificial Island

12. Box caissons Box caisson is almost the same as the open types of caissons, the only difference is that it is closed at the bottom . Box caisson is constructed on the ground surface and then it is launched in water by filling sand or gravel or concrete in the empty spaces. It is made up of timber, steel, and reinforced cement concrete ( R.C.C). Box type of Caisson foundation is generally used where the bearing stratum of the soil is available at the shallow depth.

13. Suction caissons METHOD APPLICATION Suction caissons (also referred to as suction anchors, suction piles or suction buckets ) are a form of fixed platform anchor in the form of an open bottomed tube embedded in the sediment and sealed at the top while in use so that lifting forces generate a pressure differential that holds the caisson down. They have a number of advantages over conventional offshore foundations, mainly being quicker to install than deep foundation piles and being easier to remove during decommissioning. Suction caissons are now used extensively worldwide for anchoring large offshore installations, like oil platforms, offshore drillings and accommodation platforms to the seafloor at great depths . In recent years, suction caissons have also seen usage for offshore wind turbines in shallower waters .

14. Pneumatic caissons The pneumatic types of caissons are open at the bottom and close at the top . These types of caisson foundations are specially used at the place where it is not possible to construct the well. It is used when the depth of water more than 12 m. In the construction of Pneumatic Caisson, to remove water from the working chamber compressed air is used and the foundation work is carried out in the dry condition. It can be constructed from timber, concrete, or steel. This is the fastest but the most expensive method.

15. Advantages of Caisson Foundation Caissons are economical. It is environment-friendly. There are slightly less sound pollution and reduced vibration. It is easily adaptable to varying underwater soil conditions. Caisson has high horizontal and lateral loading capacity . Minimum handling equipment is required for placement of reinforcement cage. It is sometimes used in types of soils where driving pile could not penetrate . Caissons can be reached to great depths . There is a direct and effortless way to go to the bottom by caissons to remove any kind of obstruction. Quality control of pneumatic caisson is good as it is built on dry conditions.

16. Disadvantages of Caisson Foundation The construction procedure is extremely sensitive and troublesome. It is not good for polluted sites . There is lack of qualified workers. The workers may suffer from giddiness, breaking of eardrums, bursting of blood vessels in the nose or ears and end up in paralytic death which is known as caisson disease. As the pouring of concrete is done underwater, it may not be satisfactory. The help of divers may be required .

17. Cofferdams A cofferdam is defined as a “ watertight enclosure from which water is pumped to expose the bed of a body of water in order to permit the construction for a pier or other hydraulic work.” In other words, it’s a structure that is able to retain water and pump it out into a different area . Whether it stores water or pumps it in a different location, a cofferdam ensures a dry area for construction sites.

18. Components of cofferdams Sheet piling Bracing frame Concrete seal

19. Types of cofferdams Earthen cofferdam Rock-fill cofferdam Cellular cofferdam Single walled cofferdam Doubled cofferdam Crib cofferdam

20. Advantages of Cofferdams Allow excavation and construction of structures in an otherwise poor environment. Provide a safe environment to work. Steel sheet piles are easily installed and removed. Materials can typically be reused for other projects .

21. Underwater concreting Underwater concreting is a critical concreting process performed for offshore construction . It involves the process of carefully placing fresh concrete underwater. As construction in water results in many difficulties, the start to end of an underwater construction requires special care, supervision and planning. For example, the construction of the foundation and piles to support the bridge crossing a river, or a dock construction. This is a process where the prepared concrete is poured below the water surface using suitable methods. Placement methods are: Tremie method Pump method Toggle bags Bagwork

22. Tremie method A Tremie is a watertight pipe generally of 250mm in dia. Funnel shaped hopper at its upper end and a loose plug at the bottom. It is supported on a working platform above water level.

23. Pump method Pumping concrete directly into this final position, involving both horizontal and vertical delivery of concrete. Pumping concrete has the advantage of operational efficiency with potential savings of time and labour. For massive underwater concrete construction of navigation structures, the pump method should be prohibited.

24. Toggle bags Toggle bags are ideal for small amounts of concrete placement. They are bag filled in the dry with wet concrete. Used for repair work. The concrete is squeezed out by a diver. Bagwork Bags are made of open weave material. Diver-handled bags are usually of 10 to 20 liters capacity but 1cum bags can be placed using a crane.