COFFER DAM
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COFFER DAM
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Contents
Definition
Uses
Selection of Coffer Dams
Types of Coffer Dams
Design features of coffer dams Leakage Prevention
Economic Height
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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"
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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"
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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"
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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
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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"
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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
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E#,TH +0LL C?++E,D#'S
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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
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,?CB +0LL C?++E,D#'S
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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
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T0'*E, C,0* ?, ,?CB +0LLED C,0*
C?++E,D#'S
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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
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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
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Use of Gi!e "#o$% to pre&ent t'istin( of S)eet Pi#es
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5" Dou&le wall cofferdams
> when the area to &e enclosed is large it is
necessary to provide dou&le wall cofferdam
> The dou&le wall cofferdams are of two types(
i! ?hio 4 river type cofferdams
ii! tim&er or steel sheeting cofferdams
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7" Cellular Cofferdams
> The cellular cofferdams are mostly used fordewatering large areas - where the depth of water may
&e 3A to 53 m"
>'ostly used the constuction of marine structures likeDams -Locks etc"
> The two common shapes of the cellular cofferdam
are(
i! Circular type
ii! Diaphragm type
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'?#*LE ?, SUSPE6DED
C?++E,D#'S
/here there are num&ers of repetition
work in under water foundations -such
as in the piers of multi span river &ridges - it is economical to design the
cofferdams to &e moved as a single unit
from one foundation to another"
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DES016 +E#TU,ES ?+ C?++E,D#'S
The design of a cofferdam depends on various factors such as"
i!"Hydrostatic head of /ater
ii!"Dimensions of the area to &e covered &y the cofferdams iii!"Su&soil conditions
iv!"+luctuations or of outside water level
v!"Possi&ility of erosion
vi!"Presence of ice vii!"+loating logsthe stem of a cut>down tree- etc"
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# purely theoretically designed cofferdam may fail
for factors unaccounted in its design"
Therefore -&ecome necessary to com&ine practical
knowledge or e%perience with the theoretical aspects
in the design of a cofferdam"
+or width and Depth of cofferdam ( for H 7 m- / ) /
H F 7- / ) 7 G IH>7!
/here- / ) /idth of cofferdam in
metres
H ) Height of water a&ove river &ed
in metres
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Constr$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
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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!
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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"
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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"
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SHEET PILE COFFER DAM
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SHEET PILE COFFER DAM
J Some P)oto(rap)s
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GAMMON INDIA LIMITED
CABLE STAY BRIDGESURAT
AP-02 (EXCAVATION WORK)
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Bracing welding work in
progress
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SHEET PILE COFFER DAM
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J Some P)oto(rap)s
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