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1. CONSTRUCTION AND
DESIGN OF EARTHEN
DAMS
-by Anand M Hulagabali

2. CONTENT :
 Site Identification
 Site Preparation
 Construction steps
 Design criteria
 Design of Components of dam
 Material and Machinery used
 Measures to be taken

3. SITE IDENTIFICATION
 Foundations : all types of foundation are suitable. rock type,
nature and extend of fault zones is investigated.
 Engineering surveys –topographic survey is done and various
contour plans are prepared
 Hydrological investigation- Water resources available ,
maximum flood discharge, fixation of storage capacity.
 Site for spillway – spillway is provided separately from dam
body and located in the flank.
 Quantity &quality of material available for dam construction.
considering above factors, best site is selected.

4. SITE PREPARATION
 Clearing:
It is the removal of tress, boulders, fences, buildings, and other
structures from the area. This is for the borrow pits and the area to
be occupied by the dam
 Grubbing:
It is the removal of roots, stumps and organic matter. Grubbing is
done only in the actual borrow pits and within the outline of
embankments
 Stripping:
It is the removal of all topsoil, organic materials and soft pockets
which are unsuitable for the borrow in the borrow pit areas or
unsuitable for supporting structure within the embankment outlines.

5. STEPS OF CONSTRUCTION

6. DIVERSION OF STREAM
 dewatering of place where construction is to be done.
 Firstly, temporary dam or cofferdam is constructed
which walls off and protects the site area.
 Secondly, diversion of stream is done either by
following two methods -:
 placing large pipes- if flow volume is less.
 tunnel or diversion ditch- if flow volume is large.
 diversion is done usually in summer season.

7. FOUNDATION PREPARATION
 Dewatering by pumping from sumps is done.
 For greatest economy an open excavation is used.
 Water table is be lowered so that there is never an
upward flow of water in to the excavation
 All loose materials and porous materials are
removed.
 Pits and crevices are cleaned out as deep as
possible.
 Clay or cement grouting is done if required.

8. Contd…
 Cutoff trench
A cutoff trench is excavated below the base of the fill
upstream of the centerline of the fill.
The cutoff trench is incorporated in the design for two
reasons:
 to anchor the dam to the base material.
 to prevent piping (seepage under the fill).

10. BORROW PIT EXCAVATION
 Excavation of the embankment materials,
processing them, and hauling them to the job are
important from considerations of both cost and the
quality of the materials delivered to the
embankment.
 Excavation is done either by hands or power driven
equipments.

11. FILL PLACEMENT
All objectionable materials are removed during and
immediately after the spreading operation.
• These include roots, clumps of grass and the other
organic matter, and large stones which would interfere
with compaction
• Mixing of various material is done as per design
&availability.
Moisture addition is done by sprinkling water several
hours before compaction.

12. SOIL COMPACTION
 Compaction is the process by which the required
density is obtained in an embankment. Compaction
is done to:
1) increase stiffness,
2) minimize settlements during and after
construction,
3) increase strength,
4) prevent sliding shear failure of embankment,
and
5) water tight, to obtain required imperviousness
of the core zone

13.  Contd…
 Compaction is done in stages.
 Compaction is done by following equipments :
1. Tampers
2. vibrating rollers
3. Sheep foot rollers
4. Heavy pneumatic-tired roller, etc.
Chimney drains, filters etc. are mounted in stages as dam
construction progress.

14. DESIGN CRITERIA
1. Safe against overtopping during design flood by
providing adequate spillway and outlet capacity.
2. Sufficient free board so that it is not overtopped by
wave action.
3. Seepage line should be well within d/s face so that
no sloughing of slope takes place.
4. Side slopes stable during construction and under all
condition of reservoir operation.

15. 5.Upstream slope is safe against rapid drawdown.
6.Side slopes u/s and d/s are flat enough so that the
shear stress induced in the foundation is less then
the shear strength of material.
7.D/S slope is safe during steady seepage under full
reservoir condition.
8. d/s of the impervious core is provided by suitable
drainage system.

16. 9.There is no possibility of free flow of water from
u/s through either the dam body or foundation.
10. Dam as a whole should be earthquake resistant.

17. DESIGN OF COMPONENTS OF
DAM
 Before the construction, preliminary design of
some of the components of dam is done. Following
are some of them :
 Top width
 Free board
 outer shell
 central impervious core
 D/s drainage system

18. TOP WIDTH :
 Top width is between 20-40ft.
 No dam should have top width less then 10ft (This is
minimum needed for an access road to permit
maintenance)
FREE BOARD :
 Sufficient freeboard must be provided so that there is no
danger of overtopping.
 The seepage line is well within the downstream face of
the dam.
 For any height of dam, minimum 2mtr and maximum
3mtr freeboard is provided over maximum flood level.

19. OUTER SHELL :
 Function : impart stability and protect core.
 Material : relatively pervious materials are
used which are not subjected to
cracking like SW, GW, SP, GP,
GC, etc
 Slope :
U/s slope : range – 2:1 to 4:1
D/s slope : range – 2:1 to 2.5:1

20. CORE :
 Function : core checks the seepage of water
through dam body.
 Material : material used should not have
high compressibility ,low liquid limit
& less or no organic content.
Materials like highly plastic tough
clay, silt or combination of above
can be used.
 Width of core at the crest should be minimum of 3mtr.
 Sloping cores can also be provided.

21. D/S DRAINAGE SYSTEM
 Function : reduce pore pressure in d/s portion
and checks the migration of the
particles.
 Material : sufficiently fine material to prevent
base material from clogging the
filter and coarser enough to
remove the water as early as
possible.
 3 types of drains are provided :
Toe drain.
Horizontal blanket drain.
Chimney drains.

24. MATERIALS USED
material for constructing dam is usually derived by
digging of nearby areas. Different type of materials are
used for different zones.
1. Outer shell – well graded or uniformly graded
gravel, sand, silty sand, etc...
2. Inner core – high to medium plastic clay, silt, silty
sand, etc…
3. Cut-off trench – concrete, same material as that used
in inner core (to maintain homogeneity)
4. Filter – sand and gravel placed in form of layers.

26. MACHINERY

27. Following are some the most widely used
machinery in construction of dam :
 Excavation - power shovel, dragline, scraper and
elevating grader
 hauling – trucks, wagons.
 Compaction –pneumatic tampers, sheep foot
roller, vibrating roller, heavy pneumatic-tired roller,
smooth steel drum roller.

28. MEASURES TO BE TAKEN
 Drainage is necessary for pits below ground water. This
should be done far enough in advance of the construction so
that the soil is not water logged.
 The operation of the borrow pit must be carefully
controlled for better quality
 Moisture should be controlled while placing the soil.
 Compaction must be done in layers and each layer should
be compacted to achieve about 95% of standard proctor
maximum.
 A testing laboratory is set up at the borrow pit where the
moisture content, gradation, and even plasticity can be
determined in minimum time.

29. Contd…
 Thickness of soil to be compacted in layer is
important to keep good quality of fill.
 Small compactors are effective near abutment
foundation.

30. THANK YOU…