A cofferdam is a temporary structure designed and constructed to support ground and keep groundwater or water above ground level away from an excavation. By and large, a cofferdam does not rule out hose out of dig finally since the construction of such class of cofferdam would be abundantly expensive. round about discharge of hose down into the mine is regularly well-tolerated and pumped out periodically.
There are more few types of cofferdams including earth embankment, rockfill embankment, sandbag embankment, single and double wall timber sheet pile, precast concrete blockwork, precast concrete frame unit, cellular sheet steel piling, bored cast-in-place piling, rock or earth fill timber cribs, flexible sheeting on timber or steel framing, and movable cofferdam.
Distinctive site conditions require various types of cofferdams. The variables that oversee the decision of a cofferdam for a specific building site are the water table of that territory, kind of soil, size and profundity of removal, development material accessibility, simplicity of transportation, water stream speed, and danger of harm by drifting flotsam and jetsam.
Types of Cofferdams
The nearness of specific elements at the building site prompts the decision of a particular kind of cofferdam, for instance, earth fill cofferdam is reasonable for a zone with low water head though single-divider sheet heap cofferdam is pertinent for confined site zones where ground grapple or cross propping can be utilized.
Single wall timber sheet piling
Double wall timber sheet piling
Flexible sheeting on timber or steel framing
Rock or earth fill timber cribs
Single wall steel sheet piling
Double wall steel sheet piling
Cellular steel sheet piling
Bored cast in place piling
Precast concrete blockwork
Precast Concrete frame unit
Movable cofferdams (structural steel cylinders and shells)
Criteria for Selection of Cofferdam Types
Depth of water
Depth and size of excavation
Velocity of flow in waterway
Risk of damage by floating debris or ice
Availability of construction materials
Ease of transportation of construction materials
Each sort of cofferdam gives extreme proficiency and is appropriate in specific conditions. Reasonable materialness states of basic kinds of cofferdam are talked about underneath:
It is appropriate for low head of water, and can be utilized on locales presented to streaming water if surface security is given.
Single Wall Sheet Pile Cofferdam
This kind of cofferdam is appropriate for confined site zones where ground grapple or cross supporting can be utilized. It isn’t reasonable for regions containing high amount of stones.
3. Double Wall and Cellular Sheet Piling
They are suitable for wide excavations where self-supporting dams are needed.
Shake or Earthfill Timber Cribs
These are regularly developed in a remote site in undeveloped zones where timber in bamboo or log structure are accessible, and import and exchange of sheet heap and vital plant to deal with and drive it is cosmically high.
Timber Sheet Pile Cofferdam
It is utilized in the regions where timber is promptly accessible and is reasonable for low head water.
Favorable circumstances of Cofferdams
Permit exhuming and development of structures in a generally poor condition
Give a protected situation to work
Contractual workers normally have structure duty
Steel sheet heaps are effectively introduced and expelled
Materials can normally be reused for different ventures
Weaknesses of Cofferdams
Uncommon hardware is required
Very tedious and dreary procedure of development
Whenever surged, sheets can be driven out of keeps or out of plumb
At the point when in streaming water, ‘log jams’ may happen making an additional weight on the structure
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