INTRODUCTION MAIN PURPOSE OF DAM CONSTRUCTION PARTS OF DAM FORCE ACTING ON DAM TYPES OF DAMS GEOLOGY AND FOUNDATION CONDITION GEOLOGICAL STRUCTURE AND DAM COCLUSION

1. PG DEPARTEMENT OF GEOLOGY
NAME – NIRANJAN MALLICK
ROLL NO – 22GEOL-032
CLASS – M.Sc 1st year

2.  CONTENTS
INTRODUCTION
MAIN PURPOSE OF DAM
CONSTRUCTION
PARTS OF DAM
FORCE ACTING ON DAM
TYPES OF DAMS
GEOLOGY AND FOUNDATION
CONDITION
GEOLOGICAL STRUCTURE AND
DAM
COCLUSION

3.  INDRODUCTION
DAM:
A dam is a hydraulic structure and barrier which is
constructed across river to store the flowing water
.
The earliest known dam is the Jawa Dam in
Jordan.

4.  MAIN PURPOSE TO DAM CONSTRUCTION:
-IRRIGATION
-HYDROELECTRIC-POWER
-FLOOD CONTROL
-DOMESTIC AND INDUSTRIAL WATER SUPPLY
-SEDIMENT CONTROL

5.  PARTS OF DAM
CREST- The top of the dam structure used for walk way or
road way.
PARAPET WALL- Low heighted concrete wall constructed on
the both side of the crest used as protecting wall
HEEL- Contact with the ground on the upstream side.
TOE- Contact with the ground on the downstream side.
ABUTMENT- The sloping side of the valley along which dam
is keyed.
SPILL WAY- It is the part of dam to release the excess
amount of water from the upstream side to down stream
side.
SLUICE WAY- Smaller than spill way used to clear the slit
accumulation in dam.
GALLERIES- Galleries serve as passage for checking
operation.

6.  FORCE ACTING ON DAM
WEIGHT OF DAM- The weight of the dam is primarily responsible for holding the water
back.
WATER PRESSURE- The water pressure acts perpendicular to the surface of dam on
upstream side.
UPLIFTIMENT PRESSURE- The dams are subjected to upliftment pressure under its base
due to pore water pressure.
WAVE PRESSURE- The upper part of dam , i.e . Above water level is subjected to the
impact of wave created due to wind and storm.

7.  TYPES OF DAM
ON THE BASIS OF STRUCTURE
1-GRAVITY DAM:
- These dams are heavy and massive wall like structure of
concrete in which the whole weight acts vertical downward.
-As the entire load transmitted on the small area of foundation,
such dam are constructed where rock are competent and stable.
-Suitable across narrow river channel and it can be constructed
with great height.
-This type of dam can not be constructed on weak and
permeable foundation.
- Example – Bhakra Nangal dam (Sutlej river in Himachal
Pradesh) is the highest gravity dam of India (228m).
Vertical
force

8. 2-ARCH DAM:
- These types of dam are concrete or masonry dams
which are curved or convex upstream side.
- This shape helps to transmit the major part of the
water load to the abutments.
- Arch dams are built across narrow , deep river
gorges.
- Example – Idukki dam in Kerala(Periyar river)
3- BUTRESS DAM:
-Butress dam is a thin concrete dam, supported
from the downstream side by buttresses, which may
be single or in large number
-Upstream face may be inclined or vertical.
It is a small height dam .
-Here force are transmitted directly to foundation.
Example- Roseland Dam in France.
Butress
(Fig- Butress dam)
(Fig-Arch dam)

9. 4- EMBAKMENT DAM
- Non rigid structure, built on wide valley .
- Area where earth and rock fragment are easily available.
- The force acting from upstream side are not directed transported to the
foundation rock.
- Therefore these dam are constructed on even weak foundation.
- Example- Tehri Dam ( Uttarkhanda state on Bhagirathi river)
- There are three type of embakment dam :
- * Earth fill : Made up of soil and its aggregates, has an impervious clay
core.
- * Rock fill ( Require stronger foundation than earth fill): Its built of
rock fragments and large boulders , impervious membrane is placed
over the rock in upstream side .
- * Combination of both :
(Fig – Rock fill) (Fig - Earth fill)

10. ON THE BASIS OF FUNCTION
1-STORAGE DAMS:
- Storage dam are constructed to store water during rainy season.
- Use for supply water for local wildlife and store water for
hydroelectric power generation and irrigation
2-DIVERSION DAMS:
- This type of dam are used to divert water from original course of river.
- This is constructed before the main dam.
- They provide pressure to push water into canal.
3-DETENTION DAMS:
- Detention dam are constructed for flood control.
4- DEBRIS DAMS:
- This dam are constructed by debris materils .
(Storage dam)
(Diversion dam)
(Detention dam)

11. GEOLOGICAL CONSIDERATION IN THE SELECTION OF A DAM SITES
1-NARROW RIVER VALLEY:
- If the river valley is narrow , only a small dam is required, but in case of wide river valley a large dam is required ,
so the construction cost will be very high.
2-BEDROCK AT SHALLOW DEPTHS:
-If competent bedrocks occur near the surface or at shallow depths, the foundation cost of the
dam will naturally be less.
3 – COMPETENT ROCK FOR SAFE FOUNDATION:
(a) SUITABLE OF IGNEOUS ROCK:
- The massive plutonic and hypabyassal igneous rocks is the most desirable at the dam site because
they are very strong and durable due to their dense character, interlocking texture, hard mineral
composition , occurance of negligible porosity and permeability.
- Thus all plutonic rock like granite, syenites, diorites and gabbros are very competent and desirable

12. (b) SUITABLE OF SEDIMENTARY ROCKS :
- Shale , laterite , limestone are the not favourable rock for dam construction.
- Among the sedimentary rock sandstone , well-cemented siliceous and ferruginous types are
competent and suitable for the dam foundation.
- Thick massive sedimentary formations with less porosity are desirable.
- Alternating soft and hard rocks of small thickness are undesirable.
(C) SUITABLE OF METAMORPHIC ROCKS:
- Gneisses are generally competent like granites, unless they possess a very high
degree of foliation and are richly accompanied by mica-like minerals.
- Schists are undesirable because their constituents minerals are mainly soft and
possess a very well- developed cleavage.
- Quartzites are very hard and highly resistant to weathering. They are neither porous
nor permeable.
- Slate bears a typical slaty cleavage . Hence this rock is soft and weak and undesirable
at dam sites.

13. GEOLOGICAL STRUCTURES AND DAMS
1- Horizontal beds / strata 2- Dipping / inclined beds
- Strike of the beds parallel to dam axis
- Strata dipping upstream ( Favourable site)
- The dam located on rocks dipping upstream
represent ideal foundation condition.
- Here the weight of the dam is perpendicular
to the horizontal beds . Due to the weight of
the dam there is no water percolation takes
place within the beds.
- If the basement rock are made up
homogeneous rock (quartzite) then the dam
construction is favourable .

14. 3-Strata dipping downstream
Not suitable
- The percolation of water may lubricate the junctions of rock
beds which may facilitate sliding of dams.
- The water percolating through the strata dissolves the
cementing material of rocks and enlarges the openings by
mechanical erosion. The undermines the strength of the
rocks and increases the seepage of water.
4-Strike of beds perpendicular to the dam axis.
- The best foundation condition is
when only one uniform rock is
present along the length of a dam.
- If a dam is aligned across the strike of
strata , its foundation will be on
different rock types of varying
properties.
- In such a case , there chances of
unequal settlement of the dam.

15. Nonconformity sites should be avoided due to In-homogeneity.
- Sunclinal region, dams placed on
the upstream limbs have the risk of
leakage from beneath the dam.
- Dam founded on the fault zones are most
liable to the shocks during an earthquake.
Generally the small scale fault zone can be
treated effectively by grouting.

16.  CONCLUSION
- Dams have there place – they do provide control of water ( and saving of
water in reservoir)
- Dams provide free and clean energy.
- Overall – Dams do have their place but they should be well researched
and planned before being built.
- Dams are constructed various purpose and very used to mankind.

17.  REFERENCES
Principals of Engineering Geology- K.M Bangar
Engineering and General Geology-Parbin Singh
Text book of Engineering Geology- N Chenna Kesavulu
https://en.wikipedia.org/wiki/Dam
https://www.slideshare.net/asertseminar/dams-ppt-74760074