presentation beneficial for Engineering students as well as earth sciences students.

1. Role of Engineering Geology In
Resevoirs,Dams & Tunneling
Mr. K. D. Petare
Civil Engineering Department
SRE’S Sanjivani College of Engineering,
Kopargaon 423603
UNIT V

2. Introduction
 Dams are very important structure for overall development
of humankind & so the nation.They are creating storage of
water ,not only for irrigation, hydro-power generation &
water supply.
 The wetland surrounding the reservoir area also useful for
developing & mainting Environment.
 On an average ,less then 1% of dam have encountered
accident over a long period of time.
 When dam failure history is studied thoroughly, it is relived
that there were issue in underlying foundation rocks and
those were the major source for an accident to cause.
 Therefore geological study of dam site before construction
shall be conducted thoroughly to overcome mentioned
problems

3. Physical properties & Structure of rocks
 During the selection of the reservoir site consideration
must to be given to…..
1. The amount of rainfall in area
2. Run off
3. Infiltration rate of area
4. Rate of evapo-transpiration in catchment area
5. Types of vegetation in catchment area
6. Topographical & Geological Conditions

4. Strength, Stability & Water Tightness
of Foundation Rocks
 To serve actual purpose construction of dam, it should be
the watertight, incase if foundation rocks are not
watertight,sutable measures have to be taken to prevent loss
of water through them.
 Failure of dam may result in various effect keep away such
effect safety and stability of a dam Shall be guaranteed this
basically depends majorly upon the strength and soundness
of foundation rocks.
 The strength and soundness depend on microstructure and
nature of rocks on which dam is to be founded
 The required information about rocks at the site can be
obtained by geological survey

5. Dams
 Dam is a solid barrier constructed at a suitable
location across a river valley to store flowing water.
 Storage of water is utilized for following objectives:
 Hydropower
 Irrigation
 Water for domestic consumption
 Drought and flood control
 For navigational facilities
 Other additional utilization is to develop fisheries

6. Structure of Dam
Heel
Gallery
Toe
Spillway
(inside dam)
Crest
NWL
Normal
water level
MWL
Max. level
Free board
Sluice way
Upstream Down stream

7.  Heel: contact with the ground on the upstream side
 Toe: contact on the downstream side
 Abutment: Sides of the valley on which the structure of the dam rest
 Galleries: small rooms like structure left within the dam for checking
operations.
 Diversion tunnel: Tunnels are constructed for diverting water before
the construction of dam. This helps in keeping the river bed dry.
 Spillways: It is the arrangement near the top to release the excess
water of the reservoir to downstream side
 Sluice way: An opening in the dam near the ground level, which is
used to clear the silt accumulation in the reservoir side.

8. Types of dams
Gravity dams
A gravity is a solid concrete
structure, generally having
a triangular profile, which is
so designed that it can
safely stand against the
precalculated volume of
water by virtue of its weight.
Forces in the dam : thrust of
impounded water in x-axis
and weight of the dam in y-
axis.

9. Some examples
•Bhakra Dam is a concrete gravity dam across the Sutlej
River, and is in Bilaspur, Himachal Pradesh in northern
India.
•India's second tallest at 225.55 m (740 ft) high next to
the 261m Tehri Dam.
•The 90 km long reservoir created by the Bhakra Dam is
spread over an area of 168.35 km2. In terms of storage of
water, it withholds the second largest reservoir in India,
the first being Indira Sagar Dam in Madhya Pradesh
with capacity of 12.22 billion cm3.

10. Buttress dam
Buttress dams are derived from gravity dams. This type
of dams are supported uses thin concrete slab which is
supported from downstream side by buttresses.
•It uses multiple reinforced columns to support the
dams. Since it has relatively thin structure so there is
considerable amount of saving of concrete material.

12. Arch dams
It is an arch – shaped solid structure made up of concrete which is
designed in such a way that a major part of the thrust forces acting
on the dam are transmitted to arch.

13. •Arch dams are quite thin walled dams and hence lighter in
weight.
•The Idukki Dam, located in Kerala, India, is a 168.91 m (554
ft) tall arch dam.
•It is built on the Periyar River, in the ravine between the
Kuravan and Kurathi Hills in Kerala, India.
At 167.68 metres, it is one of the highest arch dams in Asia and
third tallest arch dam. Technically, the dam type is a concrete
double, curvature parabolic, thin arc dam.
•It supports a 780 MW hydroelectric power station. It was
constructed and is owned by the Kerala State Electricity
Board.
Example

14. Embankment dams
•These are non rigid structures which are build over
wide valleys with varying foundations. These are
trapezoidal in shape and are build of single type of
material(such as earth fill or rock fill) or combination of
more than one material.
•The main advantage of these dams is that it can be
constructed on weak foundation.
•Impervious core is placed in the middle of the
embankment body.
•Generally riprap is used to control erosion.

16. •The Tehri Dam is the highest dam in India and one of
the tallest in the world.
•It is a multi-purpose rock and earthfill embankment
dam on the Bhagirathim River near Tehri in
Uttarakhand, India.
•It is the primary dam of the THDC India Ltd. and the
Tehri hydroelectric complex. The Tehri Dam withholds a
reservoir for irrigation, municipal water supply and the
generation of 1,000 MW of hydroelectricity.
•The dam's 1,000 MW pumped-storage scheme is
currently under construction.
Example

17. Influence of Geological Condition
Factor Affecting Selection of Dam
 Topography
 Geology & Foundation Condition
 Availability Of Materials
 Spillway Size & Location
 Earthquake zones
 Height Of dam
 Economically

18. Topography
 Solid Rock have strong bearing capacity such rocks are
suitable AS Foundation example granite it is suitable for
almost every type of dam and can sustain for longer period of
time.
 Earthan or rockfill type of them are prefer on gravel
foundations
Geological and foundation conditions.
 The first choice of the type of dam depends mainly on
the topography.
 An area with a narrow u shaped Valley formed by
downward erosion by river suggest a concrete overflow
Dam.
 Arch dam is suitable for an area Where water is to be
stored in a narrow V shaped Valley.

19. Availability of materials
 Importance of use material for a construction of a dam
of a cost of the project largely so availability of material
is of crucial factor in selecting types of dam
Spillway size and location
 Spillway dispose the excess of river discharge. The
capability of the spillway will depend on the magnitude
of the flood to be bypass.
 The spillway is therefore much more vital on river and
stream with huge flood potential the ability of spillway
site is very important in selection of a particular types of
dam.

20. Earthquake zone
 This factor is a crucial importance while selecting the
types of dam. earthquake zone shall be considered
while designing the dam and while selecting the types
of dam.
 The type of structure best suited to resist earthquake
shocks without danger are Earthen dam and concrete
gravity dams.
Height of dam

21. Preliminary Geological work on Dam & Reservoir Sites.
 The geology of the dam site include the foundation for the
dam and the site for other structure such as spillway,
diversion tunnel and outlet works
 Dam Foundation strength and durability to support the
type of purpose Dam, whether the foundation is watertight
and if not how much grouting will be required, whether
the spillway will require concrete lining.
 Extensive site investigation are usually required to find the
solution for this questions. No two dam site are identical as
far as geology is concerned, so each new Dam construction
project has to be investigated individually.
 To overcome all possible problem on the site there is
required to conduct preliminary study on the dam side as
follows

22.  Geological mapping of surface Rock outcrop.
 Geophysical survey.
 Subsurface survey.
 Diamond core drilling.
 Availability of material.
 petrological study.
 Metrological study.

23. Geological condition suitable for Reservoir site.
 Nature of underlying rock.
 Bed dipping upstream.
 V shaped and U shape Valley .
 High drainage density.
The location of large impounding direct supply Reservoir is very much
influenced by topography, this control the storage capacity of a
Reservoir. In addition to the factor affecting the selection of a dam site
few factor are as follows.

24. Bed dipping upstream
 For the stability of the Dam, beds dipping upstream are
most suitable location for construction.
 Dam in bed dipping upstream are most suitable for stable
foundation and for reservoir.
 Water in the Reservoir May seep through the bedding
plans, but it will retain water somewhere in upstream side
again, which serve the purpose of Dam construction.

25. Unfavorable Dips
Horizontal bed.
 The dam constructed on horizontal bed are stable compared to
the dam on dipping beds. In spite of the present situation it is
more over depends upon the underlying rocks.
 If the underlying rocks are hard, impervious Dam can withstand
for a long period and water can be stored.
 In case of pervious Rock proper Foundation with grouting on the
surface before construction shall be done.
 The water Movement in previous Rock downwards May takes
place and later natural flow of groundwater may be followed so
water may rise on the surface on the downstream side.

26. Bed dipping downstream.
 The stability of the Dam on the rock dipping downstream
depend on the rock on which the dam is founded. If Dam
Foundation is constructed on a single uniform Rock then it
is comparatively more stable then the dam foundation on
multiple layer.
 Locations where bed are dipping downstream shall be
avoided at first instance but if it is necessary to construct
dam at such location then suitable treatment procedure
shall be followed before construction.

27. Faults: Dams founded on the fault zones are most liable to
the shocks during an earthquake. Generally the small scale
fault zones can be treated effectively by grouting.

28. Folds: the effects on of fold on rock are shattering
and jointing along the axial planes and stressing
of limbs. In the synclinal region dams placed on
the upstream limbs have the risk of leakage from
beneath the dam.