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Dewatering (pronounced de-wat er-ing ) is the removal of water  from solid material or soil by wet

classification, centrifugation, filtration, or similar solid-liquid separation processes, such as removal of residual liquid from

a filter cake by a filter press as part of various industrial processes.

Construction dewatering, unwatering, or water control are common terms used to describe removal or draining groundwater or

surface water from a riverbed, construction site, caisson, or mine shaft, by pumping or evaporation. On a construction site, this

dewatering may be implemented before subsurface ecavation for foundations, shoring, or cellar space to lower the water

table. !his frequently involves the use of submersible "dewatering" pumps, centrifugal ("trash") pumps, eductors, or application

of  vacuum to well points.

Contents

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1 Dewatering by deep wells

2 Dewatering by wellpoints

3 Control of pore pressures

4 Tectonic dewatering

5 See also

!eferences

" #urther reading

#edit

$%ewatering by deep wells

 & deep well typically consists of a borehole fitted with a slotted liner and an electric submersible pump. &s water is pumped

from a deep well, a hydraulic gradient is formed and water flows into the well forming a cone of depression around the well inwhich there is little or no water remaining in the pore spaces of the surrounding soil. %eep wells work best in soils with a

permeability of k'*+ms to *ms the amount of drawdown that a well can achieve is limited only by the si/e of the

pump.#$

%eep wells can be installed in a ring around an ecavation to lower the water level and maintain a safe, dry site. 0everal

equations can be used to design deep well dewatering systems, however many of these are based on empirical data and

occasionally fail. 1ractice and eperience, along with a firm understanding of the underlying principles of dewatering, are the

best tools for designing a successful system.#2$ 0ome dewatering situations "are so common that they can be designed almost

by rule of thumb".#+$

%eep wells are also used for  aquifer testing and for groundwater drainage by wells.#3$

#edit

$%ewatering by wellpoints

4ellpoints are small-diameter (about mm) tubes with slots near the bottom that are inserted into the ground from which

water is drawn by a vacuum generated by a dewatering pump. 4ellpoints are typically installed at close centers in a line along

or around the edge of an ecavation. &s a vacuum is limited to bar, the height to which water can be drawn is limited to about

5 meters (in practice).#$ 4ellpoints can be installed in stages, with the first reducing the water level by up to five meters, and a

second stage, installed at a lower level, lowering it further.

#edit$Control of pore pressures

4hilst engineers can use dewatering to lower a groundwater table, or to drain soils, they can also use the process to

control pore pressure in soils and avoid damage to structures by base heave. 6igh pore pressures occur in soils composed of

fine silts or clays. 0ince these soils have a very low permeability, dewatering in a traditional sense (gravity flow into an

abstraction well) may prove very costly or even futile. 7nstead, a vacuum-assisted dewatering scheme, such as e8ector wells, or 

vacuum-sealed deep wells may serve to draw water into a well for abstraction.#5$

%ewatering adalah proses penurunan muka air tanah selama 9onstruksi berlangsung selain itu 8uga diperuntukkan pencegahan

kelongsoran akibat adanya aliran tanah pada galian atau bisa dipaparkan sebagai proses pemisahan antara cairan dengan padatan.

1roses dewatering tidak dapat dilakukan sekaligus, tetapi harus secara bertahap, yaitu dengan 8alan :. !hickening, ;aitu merupakan proses pemisahan antara padatan dengan cairan yang mendasarkan atas kecepatan mengendap

partikel atau mineral tersebut dalam suatu pulp sehingga solid factor yang dicapai sama dengan satu (< solid ' <)

2. =iltrasi, &dalah merupakan proses pemisahan antara padatan dengan cairan 8alan

menyaring (dengan filter) sehingga didapat solid factor sama dengan empat (< solid ' <).

+. %rying, &dalah proses penghilangan air dari padatan dengan 8alan pemanasan,

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sehingga padatan itu betul-betul bebas dari cairan atau kering (< solid ' <).

!u8uan diadakannya proses dewatering antara lain adalah untuk:

. >encegah rembesan

2. >emperbaiki kestabilan tanah

+. >encegah pengembungan tanah

3. >emperbaiki karakteristik dan kompaksi tanah terutama dasar

. 1engeringan lubang galian

5. >engurangi tekanan lateral

0elain itu, terdapat faktor penentu dalam pemilihan dewatering antara lain:

. 0ifat tanah

2. &ir tanah

+. ?kuran dan dalam galian

3. %aya dukung tanah

. 9edalam dan tipe pondasi

5. %esign dan fungsi dari struktur

@. Aencana peker8aan

9euntungan dan kerugian dilakukannya proses %ewatering:

9euntungan :

. >uka air tanah turun

2. Bongsor kurang

+. Bereng lebih curam3. !ekan tanah berkurang

9erugian :

. >ata air sekeliling turun

2. 1ermukaan tanah turun

enis dewatering dilihat dari waktu dan kegunaannya dapat dikelompokkan men8adi :

. %ewatering sementara

2. %ewatering tetapsementara

>etode dewatering

. >etode pemompaan terbuka

2. >etode alur dangkal

+. >etode predrainase

3. >etode cut off . >etode osmose elektries

Range of application of dewatering techniques

(based on CIRIA C515, London 2!

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Deepwell s"ste#

Deepwell s"ste#s

 $$$$

Deepwell dewatering s"ste#s are used to lower groundwater le%els to pro%ide stable wor&ing conditions in e'ca%ations A

deepwell s"ste# co#prises an arra" of bored wells, each fitted with a #ulti)stage electric sub#ersible borehole pu#p

In unstable granular soils wells are fitted with a liner and screen to pro%ide borehole support and allow ingress of

groundwater *ilter pac&s and grout seals #a" be required around the well liner +he pu#ps are powered fro# a central

control cabin and discharge water is nor#all" collected in a ring #ain

+he technique is particularl" suited to deeper e'ca%ations or where artesian groundwater pressures threaten base stabilit"

+he s"ste# is reliable and the wide spacing of the wells reduces access restrictions to a #ini#u#