Cofferdam- Types, Selection Criteria, and Applicability Conditions

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.

  1. Earth embankment
  2. Rockfill embankment
  3. Sandbag embankment
  4. Single wall timber sheet piling
  5. Double wall timber sheet piling
  6. Flexible sheeting on timber or steel framing
  7. Rock or earth fill timber cribs
  8. Single wall steel sheet piling
  9. Double wall steel sheet piling
  10. Cellular steel sheet piling
  11. Bored cast in place piling
  12. Precast concrete blockwork
  13. Precast Concrete frame unit
  14. Movable cofferdams (structural steel cylinders and shells)
Sheet Pile Cofferdam
Fig. 1: Sheet Pile Cofferdam
Cellular Cofferdam
Fig. 2: Cellular Cofferdam
Timber Crib Cofferdam
Fig. 3: Timber Crib Cofferdam

Criteria for Selection of Cofferdam Types

  1. Depth of water
  2. Depth and size of excavation
  3. Soil type
  4. Velocity of flow in waterway
  5. Tide levels
  6. Risk of damage by floating debris or ice
  7. Availability of construction materials
  8. Ease of transportation of construction materials

Application Conditions

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:

  1. Earthfill Cofferdam

It is appropriate for low head of water, and can be utilized on locales presented to streaming water if surface security is given.

  1. 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.

Double Wall Sheet pile Cofferdam
Fig. 4: Double Wall Sheet pile Cofferdam
  1. 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.

  1. 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

Moderately costly

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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