நீரில்லா நதியது ஒன்றில் முகம் காணத் துடிக்கிறேன் துளையில்லா குழலதில் நாளும் இசையொன்றை இசைக்கிறேன் மவுனத்தின் மொழிக்கொண்டு கவிதை நான் வடிக்கிறேன் மரமில்லா பெரும் பரப்பை வனமென்று நினைக்கிறேன் சுடுமணலில் கால் புதைத்து நிலவென்று சுகிக்கிறேன் இறையில்லா கருவறையில் தொழுதே நான் அழுகிறேன் மறுதலித்த நேசமொன்றை நெஞ்சில் சூடி அலைகிறேன் அலையாடும் கடல் மீது நிலவின் பிம்பம் காண்கிறேன் நீயில்லா நெஞ்சின் நினைவு சுவைக்கின்ற வலியது மரணத்தின் வாழ்வது.
-கோ.லீலா.
T.R அவர்களின் இது குழந்தை பாடும் தாலாட்டு எனக்கு மிகவும் பிடித்த பாடல்,எப்படி இப்படியொரு சிந்தனை என பலமுறை வியந்திருக்கிறேன்,இரண்டு கவிஞர்களை கண்டு சற்று பொறாமை உண்டு அதில் ஒருவர் டி.ஆர்,இன்னொருவர் கங்கை அமரன். வெகு நாட்களாக இப்படி ஒன்று என்னுள் உதிக்கும் என தெரியவில்லை ,இன்றைய சிறு முயற்சி....கருத்து சொல்லுங்கள்.
கொட்டும் மழை
கோடி போய்
சேரலையே
கடைகோடி
போய் சேரலையே
விதைக்காம விதை
நெல்லு முளைச்சி போச்சி
விலைப் போகாம
நெல்லும் இங்கே
தங்கிப் போச்சு
கால்வயிறு சுருங்கி
மழை நனைஞ்ச காகிதமா
ஆகிப்போச்சு
பொங்க பானை
மேலே பூனை வந்து
உறங்கியாச்சு.
தண்ணீர் திறந்து விட்டு
கண்ணீர் சிந்தும் எம்மனசு
உறக்கம் மறந்து நாளாச்சி
சட்டத்தை மாத்திடதான்
எங்கிட்ட இல்லையே ஆட்சி.
-கோ.லீலா.
அறிவு தளையிலிருந்து விடுதலையாகி
ஞானசூன்யப் பெண்ணாய்
ஒரு நாள் வாழும் வரம் வேண்டும்.
கரடேறி சுள்ளி பொறுக்கி...
நெருப்புக் கூட்டி சோறாக்கி...
ஏரி இளங் காத்தோடு
ஆல்விழுது ஊஞ்சலாடி...
அறுத்த புல்லோடு
கன்னுக்குட்டி முகமுரசி முத்தமிட
கோழியை வாரியணைத்து
மெள்ள பறக்கவிட.
நேரக்கெடு ஏதுமின்றி
ஓடையிலே முங்கியெழ.
ஓடும் மீனை கையிலேந்தி நீரில் விட...
குயிலுக்கு எசை கொடுக்க...
பூத்த மல்லி பாத்துநிக்க..
மூச்சுக்காத்துல பச்ச நெல்லு
மணம் நிரப்பிக்கொள்ள
அந்தி மயங்கையிலே
அள்ளிப் பூசிய வண்ணத்திலே
வானைக் கொஞ்சம் கிள்ளி வர
கண்ணோடு அள்ளி வர
நிலவோடு பேசி விட
ஞானசூன்யப் பெண்ணாய்
ஒரு நாள் வாழும் வரம் வேண்டும்.
அணை வழியும் தண்ணீர்கணக்கிடும்
மனம் மாய்ந்தே போகட்டும்
ஒருநாள் மகிழ்ந்தே இருக்கட்டும்.
Dear Friends Greetings ! Today let us have a look over Arch dams.
An arch dam
is a dam curved in plan and carries at major part of its water load
horizontally to the abutments by arch action.
This part of
water load depends primarily upon the amount of curvature. The balance of the
water load is transferred to the foundation by cantilever action.
The thrust
developed by the water load carried by arch action essentially requires strong
side walls of the canyon to resist the arch forces.
The weight
of arch dams is not counted on to assist materially in the resistance of
external loads. For this reason, uplift on the base is not an important design
factor.
Many early
arch dams were built of rubble, ashlar masonry, etc.
However,
practically all arch dams constructed during recent years have been built of
concrete.
The
famous Hoover Dam of U.S.A., constructed in 1936, is an an arch dam of constant
radius type having the following dimensions:
Height 222 m
(726 ft);
Length 380 m (1244 ft);
Top width 13.7 m (45 ft)
and Base thickness 201 m (660 ft).
Advantages
of Arch Dam.
1. Arch dams
are particularly adapted to the gorges where the length is small in proportion
to the height.
2. For a
given height, the section of an arch dam is much lesser than a corresponding
gravity dam. Hence, an arch dam requires less material and is, therefore,
cheaper.
3. Because
of much less base width, the problems of uplift pressure are minor.
4. Since
only a small part of water load is transferred to the foundation by cantilever
action, an arch dam can be constructed in moderate foundations where gravity
dam requiring sound foundation rock may be unsuitable.
Disadvantages
of Arch Dam.
1. It
requires skilled labor and sophisticated form work. The design of an arch dams
are also quite specialized
2. The speed
of construction is normally slow.
3. It
requires very strong abutments of solid rock capable of resisting arch thrust.
Hence, it is not suitable in the locations where strong abutments are not
available.
Unfortunately,
only few sites are suitable for this type of dam.
Types of
Arch Dams.
The arch
dams may he divided into the following types:
Classification
of an arch dam depends on its angle, radius and curvature. There are four types
of arch dams i.e. constant radius arch dam, variable radius arch dam, constant
angle arch dam, double curvature arch dam.
An arch dam
is curve shaped solid wall which is generally built with cement concrete. It is
preferred where river valleys are formed.
The working
nature of arch dam is like partly cantilever retaining wall and partly arch
action. The whole curved wall stands with its large base and transfers the
loads to the two ends of the dam using horizontal thrust.
Another
important point is that the load carrying capacity of arch dam also depends on
its curvature, i.e. greater the curvature larger will be the load resisted.
Different types of arch dams constructed and used in the world and their
characteristics are discussed below.
Types of
Arch Dam Construction
Arch dams
are generally classified into four main types:
Constant
radius arch dam
Variable
radius arch dam
Constant
angle arch dam
Double
curvature arch dam
Constant
Radius Arch Dam
Constant
Radius Arch dam, in which outer side curve of arch is built with constant radii
at all elevations. At the same time the inner curve of arch is constructed with
decreasing radius from top to bottom of dam.
The outer
side curve of an arch is called as extrodos while the inner curve is called as
introdos. Extrados always faces the upstream side and intrados faces the
downstream side.
The
thickness of dam is more at the base to withstand against hydrostatic pressure
from water and minimum thickness is provided at the top. The cross section of
constant radius arch dam look like right angled triangle in which vertical line
represents extrados and hypotenuse represents intrados.
In this type
of arch dam, all the centers of circular curves of intrados lie on same line
and on the same line the centers of extrados also lie. So, this dam can also be
called as constant center arch dam.
The constant
radius arch dams require large amount of concrete for its construction. These
are the most common types of arch dams and they are generally preferred
for U-Shaped valleys.
The central
angles of constant radius arch dam are not constant. The angle made by every
arch ring at its center vary at different elevations. The central angle is
maximum at the top of the dam and minimum at the bottom of the dam.
But there
are some recommendations in which the safest angle for an arch dam is derived
as 133o 34’. But due to its shape it is not possible to provide constant
angle throughout the dam.
Hence, this
safest angle is provided for the middle arch ring. From the middle ring the
angle will increase towards top and decrease towards base of dam. But at the
top of the dam the angle should not be more than 150o hence, during its
design the top angle is managed to below 150o.
Variable
Radius Arch Dam.
Variable
radius arch dam, as in the name itself the radii of both extrados (outer side)
and intrados inner side) curves are varied with respect to elevation. The
radius is maximum at the top of the dam and minimum at its base. In this case
also central angles of arch rings are varied at different heights hence it is
also called as variable center arch dam.
The center
line or crown line on downstream face is looks like vertical line and both
sides of this line look like battered from the top view. At abutments also, it
looks like vertical line similarly upstream side also looks vertical.
Hence, we
can provide over hangings at the crown as well as at the abutments which can
reduce the designed thickness of the dam to reduce the amount of concrete and
make it economical.
In general,
variable radius arch dam is economical than constant radius arch dam. It uses
only 58% of the amount of concrete used for constant radius arch dam. This type
of arch dam is more suitable for V-shaped valleys.
Constant
Angle Arch Dam.
Constant
angle arch dam, is a dam in which central angle of every arch ring is constant
throughout the height of an arch dam. It is obtained by the modification of
variable radius arch dam. Safe and best central angle 1330 34’ is used as
central angle in this case.
For this
type of arch dam, it is necessary to provide over hangings at the crown and at
abutments. The provision of over hangings also be done when the foundation is
stronger and is not suitable for weaker foundations.
This type of
arch dam is more economical than the above two types and requires just 43% of
the amount of concrete used to build constant radius arch dam. Constant angle
arch dam is more suitable for V-shaped valleys.
Double
Curvature Arch Dam
Double
curvature arch dam, in which curvature is provided not only in horizontal direction
but also in vertical direction. It means the cross section of double curvature
also looks like curve.
The whole
dam is looks like shell type so, it is also called as shell arch dam.
Because of
double curvature, the thickness of arch wall is reduced. But this non-vertical
type dams are difficult to construct compared to other three types. They also
require stronger foundations. Shell arch dams are more suitable for very narrow
valleys.
Why no
shutter has been provided in the arch portion of Idukki( Double curvature) dam?
Idukki dam is a double curvature thin arch dam.it means dam is curve both in X
and Y direction.look like half broken coconut.so if we provide the shutter will
be in immersed condition. So shutters are provided in cheruthoni (5 shutters).
In Tehri dam
a funnel shaped arrangement is provided at F.R.L. the surplus water will go
into funnel and reach a shaft from there through a tunnel water will be let
out. This arrangement is called "Morning glory".but Idukki is double
curvature and "thin" dam so this arrangement is not possible.
colorodo dam(Hoover dam) is single arch dam,so shutter is there.
Few important and Wonderful arch dams Enjoy the Technology.
Hoover dam's beauty at its Height.
Jingpin-I Dam i
Currently, the tallest arch dam in the world is the 305 metres (1,001 ft) Jingpin-I Dam in China, which was completed in 2013. Daniel-Johnson Dam
The longest multiple arch with buttress dam in the world is the Daniel-Johnson Damin Quebec, Canada. It is 214 meters (702 ft) high and 1,314 meters (4,311 ft) long across its crest.
