This document discusses various methods for dewatering excavation sites, including open dewatering systems using sumps and ditches, well point systems, deep well systems, vacuum systems, electro-osmosis, freezing methods, and grouting. It explains what dewatering is, why it is required, outlines different dewatering methods and considerations for selecting a method based on the size and depth of excavation, soil characteristics, and other factors. The key methods covered are well point systems, deep well systems, and freezing, with explanations of how each works and when it is suitable.

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Prepared by:
BALAR KARM P.
Asst. Professor, CED, SSASIT

2. OUTLINE

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OUTLINE

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 WHAT IS DE-WATERING??
 WHY DE-WATERING IS REQUIRED??

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WHAT IS DE-WATERING
 Dewatering means “the separation of water from the soil,” or perhaps
“taking the water out of a particular construction problem completely.”
 …in other way say that the removal of water from solid material or soil
by wet classification, centrifugation, filtration, or similar solid-liquid
separation processes. Removing water from an aquifer, riverbed,
excavation, caisson or mine by pumping.

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WHY DE-WATERING IS REQUIRED
 For construction, excavations or permanent structures that are
below the water table and are not waterproof or are waterproof
but are not designed to resist the hydrostatic pressure.
 For providing working passage for the construction.

8. A numbers of methods are available for controlling the inflow of water into an
excavation, The choice of method will depend on
 the nature and permeability of the ground,
 the extent of the area to be dewatered,
 the depth of the water table below ground level and the amount by which it has to be
lowered,
 the proposed methods of excavation and ground support,

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De-watering process

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WHAT BEFORE DE-WATERING??
 COFFER DAM
 EARTHFILL
 ROCKFILL
 ROCKFILLED CRIB
 SINGLE WALLED
 DOUBLE WALLED
 CELLULAR
 CONCRATE
 SUSPENDED
 CAISSONS
 BOX CAISSONS
 OPEN CAISSONS
 PNEUMATIC CAISSONS

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 DE-WATERING METHODS
 OPEN DEWATERING SYSTEM
 SUMPS & DITCHES
 SINGLE WELLPOINT SYSTEM
 MULTI WELL POINT SYSTEM
 DEEP WELL SYSTEM/BORED WELL SYSTEM
 VACUUM SYSTEM
 ELECTRO-OSMOSIS PROCESS
 FREEZING METOD
WELL POINT
SYSTEM

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OPEN DEWATERING SYSTEM

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 Open dewatering systems enable one to
lower the groundwater table in cohesive
and low permeable soils.
 Water is pumped off directly from
sumps (ditches) along the toes of the
slopes of the excavation works.
 The suction hose with strainer is placed
in the sump and the collected water is
discharged.
 This system easy to install and simple to
operate.

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SUMPS & DITCHES

15.  This is simplest method over other method.
 Use for shallow excavations.
 Parts: - shallow pits, called sumps which are dug along the area.
 This sump is connected by ditches which are in semicircular with 20 CM
dia.
 The water from slopes flows under gravity and it’s collected in sump
from which it will pump out.
 The height of groundwater above the excavation Bottom is relatively
small (5ft or less)
 The surrounding soil is relatively impermeable (Such as clayey soil)

16. WELL POINT SYSTEM

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 Main components are as below...
i. The well points
ii. The riser pipe
iii. The header pipe
iv. The pumps
The well point is perforated pipe 5 to 8 CM in dia & 1m long covered by
cylindrical wire gauge screen known as strainer.
 Pipes are jetted in the ground 1 to 2m a part.
 Well point → riser pipe → header →pump.

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SINGLE WELLPOINT SYSTEM
Hole 10 mt
MAX. From
pump level
Hole dia
30 Cm.
It is suitable for lowering water table by 5 to 6 m in soil.

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Multi well point system

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 When water table is greater than 6
m this method will use.
 In this method 2 or more rows of
well point are installed at different
elevation.
 In this method wells are installed
in 2 stages.
 In 1st stage water table lowered
by 5 m.
 If required, then 3ed stage of well
point can also be installed for further
lower water table.
 This method useful for up to 15 m.
For up to 15th m deep well system will
use.

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30. Typical spacing for soil types and the approximate time
required for effective drawdown

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Deep well system/bored well systemDeep well systems consist of one or more individual wells, each of which has its own
submersible pump at the bottom of the well.
lower the water table 15 m to 30 m or more in a single lift without staging.

32.  when the depth of
excavation is more
than the 16m.
 In this, 15 to 16 cm
diameter hole is bored
and a casing with a
large screen is
provided.
 A row of well points is
frequently installed at
the toe of the side
slope of the deep
excavation.
 A submersible pump
is installed at the
bottom of the well, of
which the casing
generally has a
minimum diameter of
150 mm.

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Vacuum system
When draining is required for silt or clay which have size less than 0.05mm
25 CM dia around
well point

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Electro-osmosis process

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FREEZING METOD
 Soils that will not drain using conventional methods Typically a ground
freezing system consists of an array of freeze pipes.
 that are installed into the ground around the perimeter of the
excavation, usually in a circular pattern.
 A supermodel brine solution is pump through to freeze the pipes, which
freezes the water bearing soils around the pipes to create a frozen wall.
Extreme care must be taken to make sure that the freeze is complete
because any groundwater seepage though the wall or from below the
excavation depth will have a sliding effect.

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Pipes prior to freezing
Following initiation of freeze
Closure of frozen earth wall
Complete frozen earth wall

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39. GROUND FREEZING
The procedure:
 A refrigeration plant of required installed near the site of work.
 The large pipes of 100 mm to 150 mm diameter.
 The distance between the pipes is about 1 m to 1.50 m.
 The pipes are closed at the bottom.
 The small pipes of 25 mm to 50 mm diameter are inserted into the
large pipes.
 open at the bottom.
 The cold liquid at a temperature of about -23°C to -30°C is then
circulated through the circuit. The liquid comes through the small pipe
and goes up through the large pipe.
 This causes the ground to freeze around the pipes.

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41. Considerations When
Selecting A Dewatering
System

42. Size & Depth Of The
Excavation

43. Location And
Environment

44. Proximity Of Existing
Structures

45. Existence Of Any
Contamination

46. Soil Characteristics And
Subsurface Conditions

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Grouting

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What is grouting??
Grouting is the injection of pumpable fluid materials in to a soil or rock
formation to change the physical characteristics of the formation.
Method of grouting…
 Contact Grouting
 Repair Grouting
 Chemical Grouting
 Cavity Grouting
 Consolidation Grouting

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Type of grouting method
 Permeation Grouting
 Compaction Grouting
 Jet Grouting
 Cement Grouting
 Chemical Grouting
 Polyurethan Grouting
 Vibro Compaction
 Bitumen Grouting
 Clay Grouting
 Bitumen Grouting

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Permeation Grouting
This method describes the process of filling joints or fractures in rock or
pore spaces in soil with a grout without disturbing the formation.

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COMPACTION GROUTING
Grout mix is specifically designed so as not to permeate the soil voids or
mix with the soil. Instead, it displaces the soil into which it is injected.

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JET GROUTING
The high-pressure water or grout is used to physically disrupt the ground,
in the process modifying it and thereby improving it.

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54. CEMENT GROUTING
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55. CHEMICAL GROUTING
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56. POLYURETHANE GROUTING
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57. VIBRO COMPACTION
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58.  INITIALEXCAVATION
 DRILLING OF HOLES

59.  NAILINSTALLATION
 GROUTING

60.  PLACE REINFORCEMENT ANDDRAINAGE
 SHOTCRETINGAND INSTALLING BEARING PLATES

61.  REPEAT STEPS TO FINALSUBGRADE
 PERMANENT FACING

62. Suitability of Different Methods of Ground
Water Conditions
METHOD CONDITIONS FOR SUITABILITY
1. Sumps and Ditches For shallow excavations in coarse
grained soils.
2. Well point system Suitable for lowering water table by 5-6 m
in soils
3. Bored well system For coarse grained soils and depth of
excavation more than 16 m
4. Vacuum method Draining silty sands and fine sands
5. Cement grouting For coarse materials or rocks with
cracks
6. Freezing process Suitable for excavations in water logged
soils
7. Electro-osmosis process Suitable for fine grained cohesive soils
such as clays

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 http://www.hellofrade.com
 http://www.dewateringindia.com
 http://www.groundfreezing.info
 http://www.osp.mans.edu.eg
 http://www.google.com,images
 http://www.youtube.com
REFERENCES

65. Exclusion methods: (not covered in this note)
 Slurry trench cut-off walls with bentonite or native clay and Diaphragm concrete
walls. All soils. Curtain walls around excavations with flat buckets.
 Impervious soil barrier All soils. Relatively shallow applications (5-6m max.).
Backhoes form the clay filled barriers some distance from the excavation boundaries.
 Sheet piling All soils except soils with large boulders.
 Secant (interlocked) piling or tangent piling with grouting in between. All soils
except boulders.
 Compressed air All types of saturated soils and rock. Applications in tunnels, shafts
and caissons.

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T H A N K Y O