Underwater construction
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Underwater construction

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detailed seminar report on underwater construction

detailed seminar report on underwater construction

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Underwater construction Underwater construction Presentation Transcript

  • Underwater construction 1 DEPT. OF CIVIL ENGINEERING GCET JAMMU Presented by: Abira Rather 7th sem Civil Eng. Dept. R.no: 07/10
  • Contents: 2  Introduction  Underwater construction techniques  Caissons  Types  Advantages  Dangers encountered  Cofferdams  Types  Components  Advantages  Underwater lying of concrete  Tremie method  Pump method  Toggle bags  Bagwork  Conclusion  References DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 3 During the construction of brides , dams or any other structure where the foundation part of the structure is most likely to lie underwater, we have to opt for underwater construction Construction in water poses many difficulties especially in the places where there the depth is considerable. During underwater construction our main objective is to create dry and water free environment for working in such a manner that the structural stability of the structure is not compromised. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 4 UNDERWAT ER CONSTRUC TION Constructio n techniques Caissons Cofferdams Tremie method Methods of Placing of concrete Pump method Toggle bags Bag works DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 5 Caissons: Watertight retaining structure . Permanent in nature. Used to work on foundation of bridge pier, construction of concrete dam or for the repair of ships. Constructed in such a manner so that the water can be pumped out. Keeps working environment dry. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • Working inside a caisson 6 DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • TYPES OF CAISSONS 7 Control post Open caisson grab Ground water level Circumferential gap pontoon Ballast water Box caisson shoe DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 8 PNEUMATIC CAISSON •Large inverted box on which pier is built. •Compressed air is used to keep the water and mud out. •Used to work on riverbed or quicksand's. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 9 Suction caisson • More suitable for off shore construction. • Upturned bucket embedded in marine sediment. • Embedment achieved by pushing or by creating negative pressure. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 10 ADVANTAGES OF CAISSONS Economic. Slightly less noise and reduced vibrations. Easily adaptable to varying site conditions. High axial and lateral loading capacity. Minimal handling equipment is required for placement of reinforcing cage. Placement is sometimes possible in types of soil that a driven pile could not penetrate DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 11 Dangers encountered: Caisson disease is so named since it appeared in construction workers when they left the compressed atmosphere of the caisson and rapidly re entered normal (decompressed) atmospheric conditions. Construction of the Brooklyn Bridge, which was built with the help of caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction, including the designer's son and Chief Engineer of the project. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 12 Cofferdams:  Temporary structure  Built within or in pairs across a body of water  Allows the enclosed space to be pumped out, creating a dry work environment .  Enclosed coffers are commonly used for construction and repair of oil platforms, bridge piers and other support structures built within or over water.  A cofferdam involves the interaction of the structure, soil, and water. The loads imposed include the hydrostatic forces of the water, as well as the dynamic forces due to currents and waves.  Used for shallow constructions having depth less than 10m. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • Working inside a cofferdam 13 DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 14 Components of cofferdam:  Sheet piling Sheet piling is a manufactured construction product with a mechanical connection “interlock” at both ends of the section. These mechanical connections interlock with one another to form a continuous wall of sheeting.  Brace piling  Concrete seal Sheet piles DEPT. OF CIVIL ENGINEERING GCET JAMMU Bracing frame
  • COFFERDAM CONSTRUCTION SEQUENCE: 15 1. Pre-dredge to remove soil or soft sediments and level the area of the cofferdam 2. Drive temporary support piles. 3. Temporarily erect bracing frame on the support piles 4. Set steel sheet piles. 5. Drive sheet piles to grade. 6. Block between bracing frame and sheets, and provide ties for sheet piles at the top as necessary 7. Excavate inside the grade or slightly below grade, while leaving the cofferdam full of water 8. Drive bearing 9. Place rock fill as a levelling and support course. 10. Place Tremie concrete seal . DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 16 ADVANTAGES OF COFFERDAM: Allow excavation and construction of structures in otherwise poor environment. Provides safe environment to work. Contractors typically have design responsibility. Steel sheet piles are easily installed and removed. Materials can typically be reused on other projects. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 17 UNDERWATER CONCRETING It is a process in which the prepared concrete is poured below the water surface by using suitable methods. PLACEMENT METHODS: Tremie method. Pump method. DEPT. OF CIVIL ENGINEERING GCET JAMMU Toggle bags. Bags work.
  • 18 TREMIE METHOD A Tremie is a watertight pipe Generally 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. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • Laying of concrete by using Tremie 19 Basic principle behind Method of underwater concreting Tremie method DEPT. OF CIVIL ENGINEERING GCET JAMMU Method of underwater concreting— Tremie method (inside view)
  • 20 Specifications of concrete to be used in Tremie method:  Coarse Aggregate: Gravel of 3/4” (20mm) max. size. Use 50-55 % of the total aggregate by weight.  Sand, 45-50% of the total aggregate by weight.  Cement: Type II ASTM (moderate heat of hydration), 600 lbs./yd3  Water/Cement Ratio: 0.42 (0.45 Maximum).  Water-Reducing Admixture (preferably it is also plasticizer): Do not use super plasticizers.  Air-Entrainment Admixtures: To give 6% total air.  Retarding Admixture: To increase setting time to 4-24 hours, as required.  Slump: 6 1/2" ± 1"  This mix will develop compressive strength in the range of 5,600 – 7,000 psi at 28 days. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • PUMP METHOD: 21  Pumping concrete directly into its 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 construction underwater of concrete navigation structures, the pump method should be prohibited. DEPT. OF CIVIL ENGINEERING GCET JAMMU PUMP METHOD OF LAYING CONCRETE
  • 22 TOGGLE BAGS: • Toggle bags are ideal for small amounts of concrete placement. • The bag is filled in the dry with wet concrete • Used for repair work. BAGWORK: • Bags are made of open weave material. • Diver-handled bags are usually of 10 to 20 litres capacity but 1cub.m bags can be placed using a crane. • The concrete is squeezed out by a diver. Used only in special cases like repair works, etc. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 23 CONCLUSION:  Cofferdams are temporary structures and used in cases where the plan area of foundation is very large, depth of water is less and for the soft soils, where soils allow easy driving of sheet piles.  Caissons are permanent structures and becomes economical in cases where the plan area of foundation is small, large depth of water and for loose soils.  Suction caisson anchors are gaining considerable acceptance in the offshore industry.  At present, the Tremie placement method is the standard way of placing high-quality concrete underwater. The other placement method are not able to reliably place high-quality underwater concrete for major structures, although they may find application in special cases.  For massive underwater concrete construction of navigation structures, the pump method should be prohibited. DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 24 ANY QUESTIONS?? DEPT. OF CIVIL ENGINEERING GCET JAMMU
  • 25 THANK YOU!! DEPT. OF CIVIL ENGINEERING GCET JAMMU