This presentation explains different methods of dewatering of ground water during construction works and suggests the suitability of particular method in particular context.

1. (Advanced Construction and Equipment)
Control of Ground Water in Excavation
L.D. College of Engineering, Ahmedabad-15
Semester- 6 Division-C
Guided by..
Prof. J.S. Kamble

2. Prepared by,
Sr. No. Name of Student Roll No. Enrollment No.
1. Patel Keyur 6062013 130280106081
2. Patel Vedant 6062014 130280106089
3. Patel Vishesh 6062015 130280106090
4. Patni Mo.Aamir 6062016 130280106091

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

4. 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

5. 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
2. Shallow Well System
3. Deep Well System
4. Well Point System
5. Vacuum Method
6. Cement Grouting
7. Chemical Process
8. Freezing Process
9. Electro-Osmosis Method

6. 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.
• The water from the slopes flows under
gravity and is collected in sumps from
which it is pumped out.

7. 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.

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

9. Applications for Shallow Well Dewatering
• Shallow wells can be installed with effective filters which can allow
them to pump ‘clean’ water with much lower levels of suspended
solids compared to sump pumping. This makes it easier to meet
water quality limits at the discharge point.
• Shallow wells, if installed to sufficient depth, can act as a form of
pre-drainage dewatering, where groundwater levels are lowered in
advance of excavation and can be held significantly below current
dig levels.

10. Deep Well Dewatering
 This system is more suitable when the depth of excavation is more
than the 16m or where artesian water is present.
 15 to 16 cm diameter hole is bored and a casing with a large screen
is provided. A submersible pump is installed near the bottom of the
well.

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

12. Applications for Deep Well Dewatering
 Deep well dewatering is normally suited to relatively deep
excavations where permeability is between moderate (e.g. sands) to
high (e.g. gravels).
 Deep wells can be less effective is in low permeability soils. In these
cases the well yields can be very low. Such low well yields can
make it difficult to select suitable submersible pumps that can
operate reliably and efficiently at low flow rates.

13. 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

14. Well Point System
• Well points are for lowering water table by 5-6 m in soils with a
coefficient of permeability between 10-4 to 10-6 m/sec.
• The riser is surrounded by a coarse sand filter in order to facilitate
the flow of water towards the well points.

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

16. 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.

17. 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.

18. Vacuum System

19. Cement Grouting

20. 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

22. 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

23. 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

24. Advantage
1) It can be used for sealing narrow cracks of about 0.5 mm width
2) It become hard in cold as well as warm temperature
3) It can bond the moist as well as dry surface
4) It has practically the same viscosity as water and hence it can be
injected into any soil and fine cracks into which the water can be
injected

25. GROUND FREEZING

26. Advantages and Limitations
Advantages:
• The freezing process is readily accomplished where other methods
may be difficult or impossible.
• The freezing does not affect the current water table.
Limitations:
• The area to be covered by this process should be as small as
possible.
• The freezing process is suited for work of comparatively short
duration.

27. Electro-Osmosis Process

28. 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