Cofferdam_ppt.pptx

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PATEL PRANAV R. PATEL SANJAY B. NAYI VISHAL A. BHAGAT HARSH G. PATEL DENISH D. PATEL VISHAL P. DESAI MOHIT D.

(106560306127) (106560306089) (106560306101) (116560306098) (096560306128) (116560306027) (096560306050)

Contents : Introduction  Requirement of a cofferdam  Necessity of cofferdam  Use of cofferdam  Factor affecting selection of cofferdam  Types of cofferdam  Forces acting on cofferdam  Economical height of cofferdam

Introduction : A cofferdam is a temporary

structure which is built in a river, lake etc. to remove water from an area and make it possible to carry on the construction work under reasonably dry conditions.  Cofferdams are usually required for project such as dams and construction of piers and abutment.

Requirement of a cofferdam :• The cofferdam should be reasonably watertight. • It should be generally constructed at site of work. • The design and layout of a cofferdam should be such that

the total cost of construction, maintenance and pumping is minimum. • It should be stable against bursting, overturning and sliding, under the floods and waves. • The water to be excluded by a coffer dam may be either ground water of water lying above ground level, it may be deep or shallow and still or running. • The materials used in construction of a cofferdam are earth, timber, steel and concrete.

Necessity of cofferdam : The coffer dams are required in the following situation:  When it is required to construct a structure in the river   

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bad. When structure is to be constructed on a sea shore. When it is required to construct a structure one a bank of the lake or inside the lake. When deep excavation are carried out in a course grained soil. When excavation is carried out below ground water table. During deep excavation, when sides of the trenches are likely to collapse.

Use of cofferdam  To facilitate pile driving operation  To place grillage and raft foundation  To construct foundations for piers and abutments of

bridge, dams, locks, etc.;  To enclose a space for the removal of sunken vessels  To provide a working platform for the foundation of building when water is met with; and  To provide space for carrying out the foundation work without disturbing or damaging the adjoining structure such as buildings, pipelines, sewers, etc.

Factor affecting selection of cofferdam  The selection of a type of cofferdam depends upon the     

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following factors: The size of area which is protect by cofferdam Depth of water Flow of water velocity of flowing water. The nature of bed on which the cofferdam is to rest. Availability of materials at the site The Possibility of overtopping by floods, tides etc. Transportation facility of machine equipment and materials

Types of cofferdam : Earthen cofferdam  Rock-filled cofferdams  Sand bags cofferdam  Single wall cofferdams  Double wall cofferdams  Cellular cofferdam

 Crib cofferdam  Concrete cofferdam  Suspended or floating cofferdam

Earthen cofferdam : This is the simplest form of cofferdam. It essentially consist

of an earthen embankment built around the area to be enclosed.  Suitable for low, 1.2 to 1.5 m and moderate head of water.  The top of embankment should be 1m above the water level.

Rock-filled cofferdams : Suitable for turbulent flow and up to 3m depth of water.  Stone or rubble is used for the embankment.  It construction is adopted only the stone is easily available

in the nearby areas.

Sand bags cofferdam :• The method of using laminated sand bags to

build cofferdam are easy to construct, costefficient and economic friendly

Single wall cofferdams • This type of cofferdam is used

in places where the area to be enclosed is very small and the depth of water is more, say 4.5 to 6 m. • It can be used for up to 25m depth of water.

Double wall cofferdams : Two-parallel rows of steel

sheet piles driven into the ground  Tied together with anchors

and wales, then filled with soil

 There are two types of this

type of cofferdams: 1.

ohio river type wood sheeting cofferdam

2. Wood or steel sheeting cofferdam with wales and

tie rods

Cellular cofferdams : Circular cells are connected

by diaphragms  Deep excavations  Used when the construction area is very large  Also used when internal bracing is impractical  There are two types of this type of cofferdams: 1. Circular 2. Diaphragm

Crib cofferdam •In deep water where it is difficult to penetrate the guide piles or sheet Piles into the hard bed below ,crib cofferdam is used. •In these type of construction ,the sheet piles are supported by a series of wooden cribs.

Concrete cofferdam • when construction must take place below the water level, a cofferdam is built to give works a day work environment. •sheet piling is driven around the work site, seal concrete is placed into the bottom to prevent water from seeping in from underneath the sheet piling, and the water is pumped out.

Suspended Cofferdam •cofferdam which is freely suspended and has a characteristics of floating. •it is a box type cofferdam.

Forces acting on cofferdam : Self weight of cofferdam  Water pressure

 Earth pressure from out side soil  Uplift pressure  Scouring action

 Ice pressure  Other action

Economical height of cofferdam • The maximum height of cofferdam for which its total cost is minimum is known as the most economic height of cofferdam.

• When cofferdam is constructed in a river. It is necessary to determine the height that will most satisfactory. Usually the height of cofferdam is determined based on the height of the average normal flood during every year.