1. Control of Ground Water
in exCavation
S.S.A.S.I.T, SURAT GTU
advanCed ConStruCtion & eQuiPMentSadvanCed ConStruCtion & eQuiPMentS
(2160601)(2160601)
PrePared by:-PrePared by:-
MiSS. KhuShbu K. ShahMiSS. KhuShbu K. Shah
aSSt. ProfaSSt. Prof
S.S.a.S.i.t, SuratS.S.a.S.i.t, Surat

2. Content…
• Introduction
• Dewatering methods
• Suitability of different dewatering methods

3. Introduction
• Dewatering means removal of excess water from saturated
soil.
• Dewatering is a necessary process when it comes to
many construction projects, particularly when the
construction is for underground projects.

4. Dewatering Methods
• Factors such as the type of soil and the nature of the construction
site will all influence which dewatering method will be best suited
to the project.
1. Sumps And Ditches 6. Cement Grouting
2. Shallow Well System 7. Chemical Process
3. Deep Well System 8. Freezing Process
4. Well Point System 9. Electro-Osmosis Method
5. Vacuum Method

5. Sumps and Ditches
• It is the simplest and most commonly used
form of dewatering.
• In this method, shallow pits, called sumps are
dug along the periphery of the area and
connected by drains of semicircular in shape
and 20 cm diameter.
• The water from the slopes flows under
gravity and is collected in sumps from
which it is pumped out.

6. Shallow Well Dewatering
 A hole of 30 cm diameter or more is bored into the ground to a
depth not more than 10 m below the pump level. A strainer tube of 15 cm
diameter is lowered in the bore hole having a casing tube.
 A gravel filter is formed around the strainer tube by gradually
removing the casing tube and simultaneously pouring the filter well so
formed.
 The suction pipe from a number of such wells may be connected to one
common header connected to the pumping unit.

7. Shallow Well Dewatering
[A typical layout of a shallow well
system]

8. Deep Well Dewatering (Bored well system)
 This system is more suitable when the depth of excavation is more than the
16m or where artesian water is present.
 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. The discharge pipes
from the submersible pumps of a number of adjacent wells are connected to
a common delivery main. The water is raised from the well by a multi-staged
pump.

9. Deep Well Dewatering
[A typical layout of a deep well
system]

11. Well Point System
• The main components of a well-point system are:
1. well points
2. Riser pipe
3. Swinger arm
4. Header pipe
5. pumps

12. Well Point System
• 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 2mt a part.
 Well point → riser pipe → swinger arm → header.
 It is suitable for lowering water table by 5 to 6 m in soil.

13. 13
SINGLE WELLPOINT SYSTEM

14. 14

15. Multi-Stage Well Point System
Multi-stage well point system is suitable for excavations up to 15
m.

16. 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 3rd 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.
Multi-Stage Well Point System

17. 17
MuLTI WELL POINT SYSTEM

18. Well Point System
Advantages:
•Installation is very rapid. The equipment is reasonably simple
and cheap.
•As water is filtered while removing from the ground, soil particles are
not washed away. Hence, there is no danger of subsidence of the
surrounding ground.
•As the water is drawn away by well points from the excavation, the
sides of excavation are stabilized and steeper side slopes can be
permitted.

19. Well Point System
Disadvantages:
•Single stage well point system is suitable for lowering water table by 5 to 6 m
only. For deeper excavations, where water table is to be lowered for a depth
greater than 6 m, multi-stage well point system is required.
•It is essential to continue pumping once it has been started until the
excavation is complete. If it is stopped in between, it may prove to be
disastrous.
•In case of the ground consisting of stiff clay, gravel or boulders, well points
are installed in drilled holes, which increases the installation cost.

20. Vacuum System

21. When draining is required for silt or clay which have size less than
0.05mm. That time vacuum pump system will require.
The process is as follows:
 The well-points are driven and 25 CM dia is provided around the well
point.
 Installed in the ground by forcing a jet of water under sufficient
pressure.
 The sand of medium to coarse size is then forced into
this hole as rapidly as possible. This sand forms the filter medium.
Vacuum System

22. In the upper most 600 mm to 900 mm, an impervious material
such as clay is tamped to form the seal the upper portion.
 The pumping is then carried out by means of equipment capable
of maintaining a vacuum in the well-points and the surrounding
filter.
 In this way, the pressure around the well-points is reduced to a
small fraction of the atmospheric pressure. The ground is acted
upon by the atmospheric pressure. Thus the soil becomes
consolidated under a pressure which is very nearly equal to the
atmospheric.
Vacuum System

23. In highly permeable cohesionless soil, the safety of the side slopes may be
endangered through the application of severe pumping. In such cases, especially if
control of the groundwater is required permanently, the methods of grouting can
be used.
The main idea is to insert fine materials or chemicals around the excavation in
order to reduce the hydraulic conductivity of the surrounding soil to a minimum.
In other words, the grouting process creates an almost impervious curtain around
the excavation. The grouting is conducted using movable pipes with holes. The
grout material is injected under pressure as it flows outside the pipes through the
holes to fill the voids of the surrounding soil.
The material used for grouting may be clay, cement or special chemical
compounds.
Control of Groundwater by Grouting

25. Cement Grouting

27. Cement Grouting
• The material commonly used for grout include:
1) Cement And Water
2) Cement, Rock Flour and Water
3) Cement, Clay and Water
4) Cement, Clay, Sand and Water
5) Asphalt
6) Clay And Water
7) Chemicals

29. Chemical Grouting
• The desirable properties of chemical grouts:
1)It must be able to modify the properties of soil as desired
2)It may either increase the strength or decrease the permeability of
soil
3)It must be cheap, non-toxic, non-explosive
4)It must be in the form of a liquid with low viscosity so that it can be
readily placed in the soil
5)It must be non-corrosive, so that it can be handled with
common pumps and piping
6)It must be possible to control the gel time by suitable means

31. Chemical Grouting
Inorganic chemicals
•Sodium silicate
•Calcium chloride
•Ligno-chrome
•Ligno sulphate
•They are called silicate grouts
•They are cheaper
Organic chemicals
•Epoxy resins
•Polyester resins
•They are also called resin grouts
•They possess advantage of low
viscosity, precise control of gel
time and high strength

32.  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.
FREEZING
PROCESS

33. GROUND FREEZING

34. 34

35. 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.

36. Electro-Osmosis Process

37. • This method is used for fine grained cohesive soils (such as clay), which can
be drained or stabilized using electric current. The method was developed by
L. Casagrande (1952).
• If direct current is passed between two electrodes driven into natural soil
mass, the soil water will travel` from the positive electrode (anode) to the
negative electrode (cathode). The cathode is made in the form of well point
or metal tube for pumping out the seeping form of well point or a metal tube
for pumping out the seeping water.
• A steel rod, a pipe or steel piling of excavation can serve as the cathode. The
arrangement of electrodes is done in such a way that the natural direction of
flow of water is reversed away from the excavation, thereby increasing the
strength of the soil and stability of the slope. The potentials generally used in
the process are from 40 to 180 volts, with electrode spacing of 4 to 5 meters.
Electro-Osmosis Process

38. The vibroflot is inserted into the ground and typically can be used to improve soil up
to depths of 150 feet. Vibroflotation utilizes water and the mechanical vibrations of
the vibroflot to move the particles into a denser state. Typical radial distances
affected range from 5 to 15 feet (Bauer Maschinen GmbH, 2012).
The vibroflot is suspended from a crane and seats on the surface of the ground that is
to be improved. To penetrate the material, the bottom jet is activated and the
vibration begins. The water saturates the material to create a “quick sand” condition
(i.e. temporarily liquefying the material), which allows the vibroflot to sink to the
desired depth of improvement.
At that point, the bottom jet is stopped and the water is transferred to the upper jet.
This is done to create a saturated environment surrounding the vibroflot, thereby
enhancing the compaction of the material. The vibroflot remains at the desired depth
of improvement until the material reaches adequate density.
Vibro flotation Process

39. The density of the soil is measured by using the power input (via the
electric current or hydraulic pressure) as an index. As the material
densifies, the vibroflot requires more power to continue vibrating at which
point pressure gauge displays a peak in required power.
Once this point is reached, the vibroflot is raised one lift (generally
ranging from 1 to 3 feet) and compaction ensues until the peak amperage
or hydraulic pressure is reached once again.

41. The vibroflotation process can offer the following benefits:
•When the process is done properly, it will reduce the possibility of differential settlements that
will improve the foundation condition of the proposed structure.
•It is the fastest and easiest way to improve soil when bottom layers of soil will not provide
good load bearing capacity.
•It is a great technology to improve harbor bottoms.
•On a cost-related standpoint, it helps improve thousands of cubic meters per day. It is faster
than piling.
•It can be done around existing structures without damaging them .
•It does not harm the environment. It improves the soil strata using its own characteristic
•No excavations are needed, reducing the hazards, contamination of soils and hauling material
out from the site.
Advantages

42. 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