Construction dewatering

Construction Equipments
- A project report on
Construction Dewatering…

Team members…
• Tote Vipul
• Salunkhe Harish
• Parab Shubham
• Kakamare Mrinali
• Katkam Rahul
• Thorat Omkar
• Jadhav Yatiraj
1201049
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1202016
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1202025

Definitions...
Dewatering may be defined as separation of
water from soil. OR
Dewatering may also be defined as taking the
water out of the particular construction
problem/ site.
Permanent ground water control is the
permanent stoppage of flow of water within
the ground.

Difference...
Construction dewatering
• It is separation or taking out
water from a particular
construction site.
• Purpose of dewatering is to
control sub - surface
hydrologic movement in
such a way so as to permit
construction activities in dry
environment.
Permanent ground water control
• It is permanent stoppage of
flow of water within the
ground.
• Purpose of permanent
ground water control is to
prevent entry of water in
underground constructions
during and even after
construction activities are
over.

Difference...
Construction dewatering
• It involves temporary
lowering of ground water
table at the construction
site to permit sub - surface
constructions.
• It is required only at the
time of construction.
• It is a dynamic process.
• Eg. During construction of
foundations, lift pits etc.
Permanent groundwater control
• It blocks the flow of ground
water, without interfering
with ground water table.
• It is required during and
even after construction.
• It is a static process.
• Eg. Areas of mining,
tunnels, basement, subways
etc.

Groundwater Control…
• Control of ground water always referred to
temporary and permanent exclusion.
• Temporary exclusion: lowering of the
water table and within the economic
depth range of 1500mm using subsoil
drainage methods, for deeper treatment a
pump or pumps are usually used.
• Permanent exclusion: the insertion of an
impermeable barrier to stop the flow of
water within the ground.

• Water can be classified by its relative
position to or within the ground.

• Problems of water in the subsoil:
• A high water table could cause flooding
during wet period.
• Subsoil water can cause problems during
excavation works by its natural tendency to
flow into the voids created by the excavation
activities.
• It can cause an unacceptable humidity level
around finished building and structures.

Dewatering techniques…
Pumping
methods
Sump
pumping.
Shallow well
pumps.
Well
points.
Deep
wells.
Exclusion methods
Ground freezing
Sheet freezing
Slurry trench cut-off
walls with bentonite.
Impervious soil
barriers
Grounted cut-
offs.

Sump and Sump
pumping.
• Water is collected in
deeper part of
excavations (called
sumps) and pumped
away.

Sump and Sump pumping…
ADVANTAGES-
• Simple and cheap method of dewatering.
DISADVANTAGES-
• The sump takes up space within the
excavation.
• Can lead to water pollution problems silt-
laden water.

Shallow Wells
• These are suitable
for sandy gravels
and water-bearing
rocks for depth not
in excess of 5
meters and
principle upon
which they operate
is similar to that of
well point system.

Shallow Wells
ADVANTAGES
• It is used to extract large quantities of water
from a single hole.
DISADVANTAGES
• The limiting depth to which this method is
employed is about 8 m.

Well point system.
• A line or ring of small
diameter shallow wells
(called well points)
installed at close
spacing (1 to 3 m
centres) around the
excavation.
• Commonly used for
dewatering of pipeline
trenches.

Well point system
ADVANTAGES-
• Can be very flexible and effective method of
dewatering in sands or sands and gravel.
DISADVANTAGES-
• Drawdown limited to 5 to 6 m below level of
pump due to suction lift limits.

Deep wells system
• Wells are drilled at wide
spacing (10 to 60 m
between wells) to form
a ring around the
outside of the
excavation
• An electric submersible
pump is installed in
each well.

Deep wells system
ADVANTAGES
• Effective in a wide range of ground conditions,
sands, gravels, fissured rocks.
DISADVANTAGES-
• Drawdown limited only by wells depth and
soil stratification.

Permanent groundwater Control…
• Ground Freezing Techniques
• Slurry Trench Walls
• Steel sheet Piling
• Thin Grouted Membranes
• Contiguous Piling
• Diaphragm Wall
• Precast Concrete Diaphragm Walls
• Grouting Methods

Ground Water control…
Ground freezing

Ground Freezing
• Principle: To change the water in the soil
into a solid wall of ice.
• Seepage into a excavation or shaft can be
prevented by freezing the surrounding
soil. However, freezing is expensive and
requires expert design, installation, and
operation.

Ground Freezing Techniques
• Suitable for all types of saturated soils and
rock and for soils with a moisture content in
excess of 8% of the voids.
• The basic principle is to insert into the
ground a series of freezing tubes to form an
ice wall thus creating an impermeable
barrier.
• Takes time to develop and the initial costs
are high.

Ground Freezing Techniques
• The freezing tubes can be installed vertically for
conventional excavations and horizontally for
tunneling works.
• Normally using magnesium chloride and calcium
chloride with a temperature of -15 to -25 degree
Celsius which takes 10 to 17 days to form an ice
wall 1m thick.
• Liquid nitrogen could be used as the freezing
medium to reduce the initial freezing period if
the extra cost can be justified.

Ground freezing
ADVANTAGES
• Ground freezing is an extremely versatile
method for temporary ground improvement
or cutoff.
• It is applicable to the entire range of soils,
provided that the soil is near saturation or
completely saturated.
• It is also applicable to difficult ground
conditions including large boulders and
cobbles, or debris-rich non-engineered fills.

Ground freezing
DISADVANTAGES
• Ground freezing is a highly energy intensive
process, requiring refrigeration of massive
quantities of soil over extended periods of
time, which is very expensive.

Ground freezing
DISADVANTAGES
• Ground freezing requires plenty of monitoring:
brine temperatures, soil temperatures,
deflections of adjacent or nearby structures,
heaving and settlement at the ground surface,
groundwater salinity, pressures within freeze
pipes (leak detection), frozen wall thickness, and
the location and dimensions of possible windows
within the frozen wall, among other site specific
measurements.

Slurry trench walls
• These are used to contain
or divert contaminated
groundwater from drinking
water intake, divert
uncontaminated
groundwater flow from
contaminated sites and or
provide a barrier for the
groundwater treatment
system
Slurry trench cutoff walls
Soil-bentonite
Cement –bentonite
Soil-cement bentonite

Slurry trench wall
ADVANTAGES
• This is the only method that permits the visual
inspection of key material.
• Depth up to 200ft can be reached.
DISADVANTAGES
• Large excavation site, excavated soil storage,
slurry mixing, material storage etc.
• It is hard to ensure integrity of the wall.

Cutoff wall
• Vertical barriers or “cutoff walls” are often
used in geo-environmental engineering to
control the spread of contaminants.
• Cutoff curtains can be used to stop or
minimize seepage into an excavation where
the cutoff can be installed down to an
impervious formation.

Steel sheet piling
• Steel sheet piles are long structural sections with
a vertical interlocking system that creates a
continuous wall. The walls are most often used to
retain either soil or water.

Steel sheet piling
ADVANTAGES
• It is extremely light weight and makes it easier
to lift and handle.
• Steel sheeting is reusable and recyclable.
• The pile length is easily adaptable and can be
welded or bolted to make it work

Steel sheet piling
DISADVANTAGES
• It is extremely difficult to install steel sheeting
in soil that is rocky or has large boulders.
• Driving the sheets may cause neighborhood
disturbance.

Grouted barrier walls
• It consists of injecting a fluid material at a
certain pressure into soil or rock in order to
decrease the permeability and strengthen the
formation.
• Grout walls are typically formed by overlapping
grout columns which form a single row.

Grouted barrier walls
ADVANTAGES
• Depths greater than 200 ft can be achieved.
• Little waste material is generated.
DIS-ADVANTAGES
• This configuration involves more cost.
• Relatively high hydraulic conductivity values
are obtained.

Thin Grouted Membranes
• Work as permanent curtain or cut-off non
structural walls or barriers inserted in the
ground to enclose the proposed excavation
area.
• Suitable for silts and sands and can be
installed rapidly but they must be adequately
supported by earth on both sides.
• The only limitation is the depth to which the
formers can be driven and extracted.

Contiguous Piling
• Forms a permanent structural wall of
interlocking bored piles.
• Alternate piles are bored and cast by
traditional methods after which the
interlocking piles are bored using a special
auger or cutter.
• To ensure a complete interlock of all piles over
the entire length may be difficult therefore
the exposed face of the piles is usually
covered with a mesh or similar fabric and face
with rendering or sprayed concrete.

Contiguous Piling
• Suitable for most types of subsoil and has the
main advantages of being economical on
small and confined sites; capable of being
formed close to existing foundations and can
be installed with the minimum of vibration
and noise.
• Suitable for structures such as basements,
road underpasses and underground car parks.

Diaphragm Wall
• Are structural concrete walls which can be
cast in-situ or using pre-cast concrete
methods.
• Suitable for most subsoil and their
installation generates only a small amount of
vibration and noise.
• The high cost of these walls makes them
uneconomic unless they can be incorporated
into the finished structure.
• Normally use for basements, underground
carparks and similar structures.

Pre-cast Concrete Diaphragm Wall
• Have some applications with in-situ concrete
diaphragm walls.
• Lack in design flexibility.
• The panel or post panel units are installed in a
trench filled with a special mixture of bentonite
and cement with a retarder to control the setting
time.
• This mixtures ensures that the joints between
the wall components are effectively sealed.
• To provide stability, the panels of posts are tied
to the retained earth with ground anchors.

Grouting Methods
• Are used to form a curtain or cut-off wall in
high permeability soils where pumping
methods could be uneconomic.
• The curtain walls formed by grouting
methods are non-structural therefore
adequate earth support will be required and
in some cases this will be a distance of at
least 4m from the face of proposed
excavation.

Grouting Methods
• Grout mixtures are injected into the soil by
pumping the grout at high pressure through
special injection pipes inserted in the ground.
• The pattern and spacing of the injection pipes
will depend on the grout type and soil
conditions.
• Grout types:
• Cement grouts
• Chemical grouts
• Resin grouts

240m lengthx150m
widthx21m depth

Equivalent Radius and Influence Range
Equivalent radius of excavation
r= √800ft * 500ft/√ = 357ft 112.5m
Height of water level in well
h = 160 – 70 – 5 = 85ft 25.5m
Influence range
R=C’(H-hw)√k =3000*(140-85)*0.3*√9.2*10^-5
=2200ft 670m
C= 3000 for wells

Rate of flow in wells
Multiple wells
For circular arrangement of wells
Q = 3.14k(H^2-h^2) / ln R – ln r
=3.14 * 0.00181*(140^2 – 85^2) /
ln 2200 - ln 357
= 38.7 cubic ft /min = 290gal / min
= 290/8 = 36.3 gal/min per well

Multiple Wells
Deep wel l size:
4” dia. for 36.3 gal/min
Header pipe:
4” dia. for 5*36.6 gal/min=181 gal/min
Discharge pump:
4” dia. Pump for 290 gal/min

THANK YOU…
Questions please…

Construction dewatering

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