Who builds dams ??? by shanpk

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									NATIONAL TECHNICAL UNIVERSITY OF ATHENS
LABORATORY OF MATERIALS
OF CONSTRUCTION




   Dams- materials-
 environmental impacts
                    Emil. Koroneos, Professor

             G. Poulakos, Associate Professor

             G.-Fivos Sargentis, Civil Engineer




            December 2004
Hydrologic cycle

Dams

   Dam failure

   Basic forces on a concrete dam

  Dam types

Material testing for concrete dams

Environmental impacts-case study
What is a dam:
A dam is a structure built across a stream, river or estuary
to retain water.
There is no unique way to retain water, which is why we
see many different shapes for dams. Some dams are tall
and thin, while others are short and thick.
Dams are made from a variety of materials such as rock,
steel and wood. We will concentrate on dams made from
concrete, a complex material, because it is important for
the construction of large dams.
 Who builds dams
Dams are really the product of many people, but civil
  engineers are usually key players.


 What is a Societal Structure
Societal structures are those whose performance - including catastrophic
  failure - has a large impact on a significant population.

An obvious example of a societal structure is a bridge. A bridge provides
  a large number of people with a convenient way to cross a river.
  Another example is a highway, something that isn't usually thought of
  as a structure but also needs to be built and maintained because it can
  affect a large population.
HYDROLOGIC CYCLE
The earth's water supply remains constant, but man is capable of altering the cycle of
that fixed supply. Population increases, rising living standards, and industrial and
economic growth have placed greater demands on our natural environment. Our activities
can create an imbalance in the hydrologic equation and can affect the quantity and
quality of natural water resources available to current and future generations.
DAMS
Dams gather drinking
water for people




Dams help farmers bring
water to their farms




Dams help create power
and electricity form water
Dams keep areas form
floating




Dams create beautiful
landscapes and space for
pleasure
                                   Dams failure
Over 100 years ago, a catastrophic dam failure caused thousands deaths in Harrisburg
(Pennsylvania).


Before the failure:




and after
 A Tragic Display of Strength
The great reserves of strength inherent in an arch dam were dramatically
displayed in 1963 when the reservoir behind Vaiont Dam in Italy was virtually
destroyed by a landslide. Vaiont, at that time the second highest dam in the
world, was built across a narrow gorge on limestone foundations so that the
crest 858 feet above the valley bottom was only 623 feet in length. Some
large-scale instability in the mountainside above the reservoir had been
observed earlier by the engineers during filling.

They were allowed to proceed very slowly, and three years later, on Oct. 9,
1963, with filling still incomplete, about 314 million cubic yards of soil and
rock slid down into the reservoir, sending a tremendous volume of water to a
height of 853 feet on the opposite side of the valley. The flood overtopped
the dam to a depth of 328 feet and surged down the valley, causing a major
tragedy, the destruction of several villages with a large loss of life. Yet, only
superficial damage was caused to the dam, which, at its crest, is about 11.2
feet thick.
         Basic forces on a concrete dam



The main forces on a dam.
  • forces of the reservoir water
  • uplift force
  • weight of concrete
Beside these main forces, there are many other forces that may act
on a gravity dam:
• there may be water on the downstream side of the dam as well;
this water will have the same sort of vertical and horizontal forces
on the dam as the water on the upstream side
• internal hydrostatic pressure: in pores, cracks, joints, and seams
• temperature variations
• chemical reactions
• silt pressure; silt will build up over time on the upstream side; silt
provides about 1.5 times the horizontal pressure of water and twice
the vertical pressure of water
• ice load on the upstream side
• wave load on the upstream side
• earthquake loads
• settlement of the foundation or abutments
• other structures on top of the dam -- gates, a bridge, cars
• creep of concrete: deformation of the concrete when under a
constant load for a long period of time.
Dam types
Gravity dams
Arch dams
 An Introduction
to Gravity Dams
Massive dams (material-concrete)
that resist the thrust of water
entirely by their own weight.

Most gravity dams, like the Grand
Coulee Dam in Washington, are
expensive to build because they
require so much concrete.

Still, many people prefer its solid
appearance to the thinner arch
dams.
                            Embankment dam

They are massive dams made of earth and rock. Like gravity dams of concrete,
embankment dams rely on their heavy weight to resist the force of the water. But
embankment dams are also armed with a dense, waterproof core that prevents water
from seeping through the structure.
In 1850, French engineer J. Augustin
Tortene de Sazilly (1812-1852) showed in
a lecture that the most advantagous profile
for a gravity dam is triagle with a verticle
upsteam face. Sazilly also analyzed three
recent French navigation dams in a paper
published posthumously in 1853. He used
the cross sections of these three dams to
illustrate the confusion and uncertainty in
the design of gravity dams. In fact, two of
                                               The Triangular Gravity Dam
the dams were wrongly inclined on the
upstream side!
                              The parts of a gravity dam




Gravity dams use their weight to hold back the water in the reservoir. Gravity dams can be made of
earth or rock fill or concrete. In this section we will concentrate on concrete gravity dams. These dams
can be very expensive because of how much material they use.
Generally, the base of a concrete gravity dam is equal to approximately 0.7 times the height of the
dam:
base = 0.7 * height
The shape of the gravity dam resembles a triangle. This is because of the triangular distribution of the
water pressure. The deeper the water, the more horizontal pressure it exerts on the dam. So at the
surface of the reservoir, the water is exerting no pressure and at the bottom of the reservoir, the water
is exerting maximum pressure. The shape can vary slightly; any of these shapes can be used for a
simulation of a gravity dam if the exact shape is not known.
                             An Introduction
                             to Arch Dams




An arch dam is a curved dam which is dependent upon arch action for its strength.
Arch dams are thinner and therefore require less material than any other type of dam.
Arch dams are good for sites that are narrow and have strong abutments.
              The parts of the Arch dam




Arch dams are usually made of concrete and are very
suitable for narrow gorges with strong abutments. The
gorge is often in the shape of a V; less often it is a U-
shape. Arch dams use much less concrete than gravity
dams. The best design is a double-curved arch.
          Materials: The Return of Concrete

Concrete -now on the basis of Portland cement- was used
for the first time since the Romans for the Boyds Corner
gravity dam completed in 1872 in New York . The Lower
Crystal Springs Dam in California, completed in 1890, was
the first dam in which the water content of the concrete was
specifically controlled. Because the cement industry was
nonexistent in California, the cement had to be imported
from England. In 1892 in France and in 1918 in the United
States it was scientifically determined that by decreasing the
amount of water and increasing the amount of cement in
concrete, it became stronger. However, a minimum amount
of water must be there to ensure the workability of concrete
while the amount of cement may need to be limited on
account of the heat it develops during the hardening
process.
MATERIAL TESTING
Fracture
                  Brittle

                            Duractile




                                        Schematic
                                        representation of
                                        tensile stress-strain
                                        behaviour for brittle
                                        and duractile materials
Stress




                                        loaded to fracture.


         Strain
Many structures are made of steel and/or concrete, and both of these
materials can fracture.

Civil engineers use both steel and concrete, so they must be concerned
with fracture.

In steel, fracture is often ductile and may be due to fatigue.

A fatigue crack is caused when a cyclic load is applied. You are applying a
cyclic load to a soda can tab when you push it back and forth to break the
tab off of the soda can.

"Ductile fracture" means that the part of the material which is cracking is
also deforming (its shape is changing). Think of pulling a piece of silly putty
into two pieces: as you pull it apart, it deforms until you have created two
new pieces.
On the other hand, concrete fracture is brittle. Brittle fracture means there is no
deformation around the crack; the very grains of the material are separating, or
cracking themselves.

Concrete is the material of choice for many, many structures: buildings, bridges,
dams, to name a few. Concrete offers many advantages: low cost, good
weather and fire resistance, good compressive strength, and excellent
formability. Concrete is bad in tension and therefore prone to cracking. Also, it's
behaviour is not so predictable.

Many dams are made of concrete and have suffered from cracking, which is
caused by many different forces

Concrete is not found in nature the way we would find aluminium, nickel or iron.
Concrete is formed from combining water, a special cement and rock:

PORTLAND CEMENT + H2O + ROCK = HARDENED CONCRETE + ENERGY(HEAT)

Heat? Yes, and lots of it if your concrete structure is big. The heat, and
temperature variations in general, can cause cracking problems.
 Typical Composition by
          Volume
Cement            7-15%
Water            14-21%
Aggregate        60-80%
Compressive Strength Test

For this test, concrete is poured into a cylinder. The cylinders are
    usually steel. The cylinders filled with concrete are allowed to cure
    at 20 degrees °C for 28 days. Then each cylinder is loaded axially in
    a laboratory: the cylinder is stood up in a loading machine and an
    arm of the machine pushes down on the top of the cylinder until the
    cylinder breaks. The maximum amount of force the machine used
    on the cylinder is important. The compressive strength of the
    concrete, f'c is given by:
f'c=P/A
where P is the load at which the cylinder failed
    A is the cross-sectional area of the cylinder,
    in this case, π*r2
    where r is the radius of the cylinder
Split Cylinder Test

This test uses the same type of cylinders as are used in the
    compressive test from above. But instead of standing up
    in the loading machine, the cylinder lays on its side. The
    machine pushes down on the free side of the cylinder.
    The cylinder will split in two halves. Based on the load at
    which the cylinder split, you can compute a tensile
    strength, fct, of the concrete. The equation is:
fct=2P/(πdL)
where P is the load at which the cylinder failed
    d is the diameter of the cylinder
    and L is the length of the cylinder
Permeability of materials
This test uses cubes. The
   upper side of cube gets       Insulating
   water with hydraulic           material
   pressure.
After 3,6,12 hours of the test
   we are calculating the
   volume of the absorbed
   water in the material.
With this test we can have
   relatively results about
   the behavior of the
   materials according to
   water.
Volume of water




                         Better
                         material


                  Time
Materials corrosion
The more constant form of matter, and consequently the
maternal raw material of structural materials are the rocks,
the minerals.

With this form we can see the materials in nature in
combination with the local natural environment. Raw
materials are found in a situation of balance, both chemical
and natural.

They cannot be degraded through natural activities because
they have already suffered all the changes imposed to them
by nature, by the local environment and the various episodes
(natural reasons) such as earthquakes, volcanos’ explosions,
downpours, tides, heat, etc.
If we treat maternal materials and turn them into structural
   materials, the structural materials are energetically
   upgrading.



With the contribution of the environment in which they are
  placed, the conditions are created for the awakening and
  their inclination for natural, mechanical, chemical, and
  biological changes, or as we may say: their corrosion.
Factors of corrosion

Humidity, rain, ice
Solar radiation
Electrolytes, marine electrolytes, (salts)
Wind, dust, soot and harmful gases, which are
mainly:
  Carbon dioxide
  Sulphur dioxide
  Nitrogen oxides
Changes of temperature
Ice cycle




            Icing 75 min         Freezing 30 min

    -20 º C                0ºC             20 º C


        shower                    shower
     defreezing 15 min            heating 30 min
              Change of volume




Temperature
Gas cycle CO2, SO2




                      30 min
                  Corroded air gas
    20 º C                                       20º C
                      30 min
        Diphase material, liquid and air phase
Calculate a crack

The ways to calculate a crack, how it begins, how it grows,
  and if it stops, are all part of the field called fracture
  mechanics.

There are many, many ways to try to calculate a crack. In
  fact, people are still fighting about which way is the right
  way. The right way really depends on what kind of
  material and what type of structure you're talking about.
  Here we'll discuss a version of fracture mechanics which
  can be applied to large concrete structures, like dams.
   Forces
There has to be some sort of force acting on a material to
  make it fracture. There are three major forces to consider:

  Temperature variation -- this can be a big problem in
  concrete. As you learned earlier in the section on concrete,
  when concrete is mixed it gets very hot and expands. When
  it tries to cool off, the concrete wants to contract. If it can't
  contract (because it is connected to another wall or rock)
  then cracks form.

  Chemical reaction -- a reaction between the cement and the
  aggregate in the concrete which makes the concrete "grow”

  Live load -- the general pulling or pushing on a material. In a
  dam, loads could be caused by settling or sliding of the
  foundation or abutments, ice, silt, waves, earthquakes, or
  even bombs
Modes

These forces are simplified into three
 different "modes", basically three ways the
 forces can act and what kind of fracture
 they cause
Mode I: the forces are perpendicular to the crack (the crack is horizontal
and the forces are vertical), pulling the crack open. This is referred to as the
opening mode.
What would happen if both of the forces were pushing down on the crack?
Nothing. This would close the crack.

Mode II: the forces are parallel to the crack. One force is pushing the top
half of the crack back and the other is pulling the bottom half of the crack
forward, both along the same line. This creates a shear crack: the crack is
sliding along itself. It is called in-plane shear because the forces are not
causing the material to move out of its original plane.
In this case, what would happen if both the forces were moving in the same
direction, both forward or both backward? This would not cause the crack to
grow, since all of the material would be moving in the same direction.

Mode III: the forces are perpendicular to the crack (the crack is in front-back
direction, the forces are pulling left and right). This causes the material to
separate and slide along itself, moving out of its original plane (which is why
its called out-of-plane shear). The forces could also be pushing left and right
and the same effect would occur. But the forces have to be moving in
opposite directions in order to grow the crack.
Mode I cracking happens in concrete dams. If there is an existing crack
  on the upstream side, water can enter and open the crack:
KI and KIc

How do we describe what's happening during Mode I
  cracking? To help us do this, there is something called a
  stress intensity factor, which has the symbol KI.

  KI is basically a measure of the likelihood that the crack
  will grow when the opening forces are being applied.
  Think of KI as the crack's money: if the crack has enough
  money, then it can do what it wants, which is grow. How
  much money the crack has, KI is based on the load on
  the structure and the initial size of the crack.

  Now KIc is a material's resistance to crack growth. KIc
  tells you when the material will allow a crack to grow.
  This is a property which can be measured in a
  laboratory.
Energy
Another way to think about cracks is in
  terms of energy. What kind of energy
  and where does it come from? When
  a material is being pulled, like this
  one, the material gets some energy.
When a dam is being pushed on by the
  reservoir, the dam must do work to
  hold the water back. This work is the
  stored energy in the dam.
Cracks use up some of this stored
  energy when they grow in a dam
Cracks in dams
   RCC dams

The construction of dam using Roller Compacted Concrete
(RCC) technology with high doses of fly ash.

Approximately 60-70% cement is being replaced by fly ash.

The dams constructed under this project using RCC
technology with high doses of fly ash, includes dams of
height about 90m.
Coal Creek Station, owned by Great River Energy (Elk
River) is located near Falkirk Mine in Underwood,
N.D. It is one of the largest lignite-fired generating
plants in North America with 650-foot tall chimney
(almost as tall as the IDS Tower in downtown
Minneapolis)
CASE STUDY: N. Plastiras Lake
                     Introduction



The lake, situated in a mountainous part of Western Thessaly,
is a multipurpose reservoir used for hydropower, irrigation,
water supply and recreation.

These competitive uses raise various conflicts between groups
of different interests (farmers, residents, ecologists, hotel
owners).
Water basin




The dam
Characteristics of the water basin and the reservoir



  Basin area 161.3 km2
  Maximum basin altitude 2140 m, mean altitude 1459 m
  Mean annual runoff 147 hm3 (1029 mm)
  Arch dam, height 83 m
  Reservoir capacity 362 hm3, net capacity 286 hm3, maximum
  area 25 km2
  Intake level +776 m, spill level +792 m
  Installed power capacity 130 MW hydraulic head 577 m
  Annual water demand 160 hm3 (145 hm3 for irrigation, 15 hm3
  for water supply)
Reservoir operation analysis through
  a stochastic simulation approach


       Water quality analysis



        Landscape analysis
Reservoir level at
    +783 m
Level at +792 m (= spill
level, photo digitally
processed)
Reservoir level at
    +783 m
Level at +792 m (= spill
level, photo digitally
processed)
Field research
Photographs were taken
systematically from specified
observation positions so that we
could estimate the changes of the
landscape following the water-
balance of the lake.
Other problems to the landscape
 Road design
 Time programming of traveler
 Point of observation of traveler
Residential development
As the concept of the following statue presents:
      Nature will wriggle out of any norm.
Environment-Ecology
    and morality
“We must be the leaders and the owners of the
nature”
               Rene Descartes (1596-1650)



“We must learn to respect the earth of our
children
This respect must be our new morality”

           Friedrich Nietzsche (1844 – 1900)
   “Our society is abusive and bedrock foolish “
                     K. Kastoriadis (1922-1997)




“It is rather immoral to wait for a building to take fire
 in order to have the criteria on how to study the new
                 provisions of safety”
                                 D. Canter

								
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