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COFFER DAM



Contents

Definition

Uses

Selection of Coffer Dams

Types of Coffer Dams

Design features of coffer dams Leakage Prevention

Economic Height



Definition

Cofferdams are temporary enclosures to keep out water

and soil so as to permit dewatering and construction of the

permanent facility structure! in the dry"

# Coffer Dam is a temporary structure designed to keepwater and $or soil out of the e%cavation in which a &ridge

pier or other structure is &uilt"

'eaning of Coffer Dam ( Coffer ) *o%

To take up the +oundation works in the 'arine ,egion- itis necessary to o&struct the water flow &y means of Coffer

Dam"



PURPOSE TO USE COFFER DAM STRUCTURE

To retain Soil . /ater

Can &e used as either Temporary or Permanent

'ain purpose is to provide dry working area for workers

0t is constructed to facilitate pile driving operations"

0t is used to place grillage as well as the raft foundations

0t is used -when the foundations for piers and a&utments of a &ridge-

dams- locks- etc" are to &e constructed"

Some times it is also provided to store water temporarily"



Cofferdams can &e used in all the sectors as e%plained &elow"

Civil Engineering( Underground Car Parking- +oundation-*asement Construction

Transport Engineering( *ridge Pier- Support /alls- ,amps-

1round /ater ,etention- Tunnel /ork etc"

/ater Engineering( /eirs- Culverts- +lood Protection

/alls- Scour Protection /alls- Securing Em&ankment etc"

Port Construction( Dock /orks- 2etty /orks etc"



SELECTION OF TYPES OF COFFERDAMS

3" Low heads of water 4 earth fill cofferdams

5" 6arrow E%cavations 4 single wall sheet pile

cofferdams otherwise dou&le wall cofferdamsor cellular sheet piling are suita&le for wide

e%cavations

7" The materials availa&le at site of work for

construction

8" The possi&ility of overtopping &y floods- tides-

etc" and sliding 4 rock filled cri& cofferdams



9" The nature of &ed on which the cofferdam is to rest 4

deep deposits of soft clay- # heavy earth filled cri& or

cellular cofferdam could not &e suita&le &ut singlewall sheet pile would &e re:uired in these conditions"

;" The nature of velocity of flow-i"e" water flowing with

slow current or with swift current

<" The chances of &ed erosion due to reduction of water

way caused &y the construction of a cofferdam"

=" The facilities availa&le for the transport of e:uipment

and material re:uired for the construction of acofferdam"



Types of Coffer Dam

3"Earth fill cofferdams > mainly for low level water 5" Sand *ag Coffer Dam 4 to divert coarse of water

7",ock fill cofferdams

8"Tim&er Cri& or rock filled cri& cofferdams >

Construction on land and than floated into place-which is also known as 1ravity Dam

9"*raced $ Sheet Pile Coffer Dam> Consisting of Sheet

Piles- mainly used in shallow water depth

i!" Single wall coffer dams

ii!" Dou&le wall coffer dams

iii!" Cellular cofferdams

;" 'ova&le or suspended cofferdams



E#,TH +0LL C?++E,D#'S



Suita&le for rivers or streams having shallow depth of

water- a&out 35@ to 39@ cm- with low velocity of flow

0t is the simplest type of cofferdam"

+ree &oard 4 ;@ to A@ cm

Top width of earth dyke 4 one meter

Suita&le side slope should &e provided

Provided suita&le drain

0ts depends on soil availa&ility and site conditions"

Dry conditions 4 clay em&ankment provided

/et condition 4 sand materials suita&le



,?CB +0LL C?++E,D#'S



The construction of rock fill cofferdams is similar to

earth fill dams 0t can &e constructed with steeper slopes

/ater depths 4 7 m"

0n case of high heads of water - this can &e achieved

&y a clay or concrete care wall

0mpervious layer providedconcrete or caly corewall

or sheet pile ! for reducing entry of seepage



T0'*E, C,0* ?, ,?CB +0LLED C,0*

C?++E,D#'S



0t consists of tim&er cri&s made from logs of wood

Constructed on land and floated into place 0t consists of a unit or a cell open at the &ottom and

having the framework of horiontal tim&er mem&ers"

Hollow space thus formed are then filled with rock orgravel

Depth of water 4 3@ to 5@ m

Used for wide e%cavation and rocky river &ottoms



SHEET P0LE C?++E, D#'

3" Single wall cofferdams

>it used in places- where the area to &e enclosed is very

small

>depth of water is more ) 8"9 to ; m

> # single row of sheet piles is provided on the whole

length of the cofferdam

> 1uide piles- /ales and struts wood!

> guide piles are first driven deep in the river &ed andspacing &etween them 3"= to 7"@ m

> The sand &ags are stacked on the inside and outside faces

of the sheet to increase the sta&ility of cofferdam



Use of Gi!e "#o$% to pre&ent t'istin( of S)eet Pi#es



5" Dou&le wall cofferdams

> when the area to &e enclosed is large it is

necessary to provide dou&le wall cofferdam

> The dou&le wall cofferdams are of two types(

i! ?hio 4 river type cofferdams

ii! tim&er or steel sheeting cofferdams



7" Cellular Cofferdams

> The cellular cofferdams are mostly used fordewatering large areas - where the depth of water may

&e 3A to 53 m"

>'ostly used the constuction of marine structures likeDams -Locks etc"

> The two common shapes of the cellular cofferdam

are(

i! Circular type

ii! Diaphragm type



'?#*LE ?, SUSPE6DED

C?++E,D#'S

/here there are num&ers of repetition

work in under water foundations -such

as in the piers of multi span river &ridges - it is economical to design the

cofferdams to &e moved as a single unit

from one foundation to another"



DES016 +E#TU,ES ?+ C?++E,D#'S

The design of a cofferdam depends on various factors such as"

i!"Hydrostatic head of /ater

ii!"Dimensions of the area to &e covered &y the cofferdams iii!"Su&soil conditions

iv!"+luctuations or of outside water level

v!"Possi&ility of erosion

vi!"Presence of ice vii!"+loating logsthe stem of a cut>down tree- etc"



# purely theoretically designed cofferdam may fail

for factors unaccounted in its design"

Therefore -&ecome necessary to com&ine practical

knowledge or e%perience with the theoretical aspects

in the design of a cofferdam"

+or width and Depth of cofferdam ( for H 7 m- / ) /

H F 7- / ) 7 G IH>7!

/here- / ) /idth of cofferdam in

metres

H ) Height of water a&ove river &ed

in metres



Constr$tion Se*en$e of

Coffer Dam +,-Dri&in( of Gi!e Frame

.-Lo'erin( of S)eet Pi#e

/-Dri&in( of S)eet Pi#e0-1ori2onta# "ra$in( 34a##er 5 Strt

arran(ement6 to 'it)stan! t)e #oa!

$omin( on s)eet pi#es from otsi!e-

7-E8$a&ation an! P#( in Con$rete toresist p#ift pressre

9-Reinfor$ement an! Con$rete 'or% of

t)e Permanent Str$tre



COFFER DAM

J +actors governing the Economic Height of Coffer Dam

J 3"Depth of /ater

> Low depth )F Earthen Dam> High Depth )F Sheet Pile Coffer Dam

J 5"Current and nature of flowering of Sheet Pile

> High Current )F Sheet Pile Coffer Dam

Higher Seepage Control Capacity!> Low Current )F Earthen or any other Dam

Less Seepage Control Capacity!



J 7"Type and Period of /ork

> Short Duration /ork )F Tim&er Dam

> Long Duration work )F Sheet Pile Coffer

Dam

J 8"High and Low Tide Level of ,eservoir

> Sheet Pile must have top level slightly higherthan that of the HTL" So that even in

e%treme case water can not over top the

coffer dam- to achieve the dry working

through out the season"



J 9"Scour Level of ,eservoir

> Scour level can &e considered as the &ottom

most layer of the loose soil of river *ed Level"

> Up to Scour level there are chances of erosion

due to the current of water" 0n any Pile or /ell

foundation- the care to &e taken that thefounding level must &e &elow the scour water

level

J ;"Type of 'aterial to &e used

> Structural Sheet pile is costly &ut can &e reused

at different proKects"



SHEET PILE COFFER DAM




J Some P)oto(rap)s



GAMMON INDIA LIMITED

CABLE STAY BRIDGESURAT

AP-02 (EXCAVATION WORK)



Bracing welding work in

progress



J Some P)oto(rap)s



YOUTHANK

cofferdam conversion gate01

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