The dam is
taking shape in three sections;
(1) a mid-river spillway flanked by (2) a left bank powerhouse
and dam and (3) a right bank powerhouse and dam. Because of the
way the river was diverted, construction is currently being
concentrated on the spillway and the left bank powerhouse dam. The river
flows from west to east.
The Three Gorges Dam
is the biggest concrete gravity dam in the world. The gravity dam is the dam that the stability almost depends on the weight of the dam itself. The Three Gorges Dam is 2335 meters (1.46 miles) long and has a crest
elevation of 185 meters and maximum height of 175 meters above the sea level. The Three Gorges Dam
used 27.2 million cubic meters of concrete, 463000 tons of steel and moved
about 102.6 million cubic meters of earth. Such a lot of steel and concrete makes
the dam extremely tightly connects and combines with the tunnel and coasts of
the river.
Gravity dams including the Three Gorges
Dam are usually triangular shapes. They have the vertical upstream face,
uniformly sloped downstream face and grout curtain. The major forces existing
are gravity of dam, force of reservoir and the uplift force. The other forces such
like the thermal stress; internal structural forces and sedimentation pressure
are also included.
Figure: Free body diagram of gravity dam
http://www.cv.titech.ac.jp/~courses/atce2/dam.pdf
For the specific
forces existing on the Three Gorges Dam, there are two directional forces that
could be calculated, force of the gravity of the dam and the horizontal
pressure of water.
Force of gravity of
the dam
Concrete volume = 27.94*106 m3
Density of concrete = 2407.82 kg/m3
Therefore, the mass of the dam could be calculated by
multiply the volume and density.
Mass = 6.727*1010 kg
Force = mg =(6.727*1010 kg)(9.8 N/kg) = 9.599*1011
N
Horizontal Pressure
of water
The formula the calculate the pressure is P=ρgh
Upstream: Depth (1/3)*175 m = 58m
Density of water ρ = 1kg/m3
P =ρgh = 1 kg/m3 *9.8 N/kg *58 m = 568.4 N/m2
Downstream: Depth (1/3)*83 m = 28m
P = 1 kg/m3 *9.8 N/kg *28 m = 274.4 N/m2
Due to the Newton’s
3rd Law- action/reaction, the uplift force exists due to the gravity
force and other outside pressures and reacts the same force to support the dam.
The The Three Gorges
Dam has huge a reservoir which is on average about 660 kilometers in length and
1.12 kilometers in width. It contains 39.3 cubic kilometers of water and has a
total surface area of 1045 square kilometers.
The huge reservoir
made a security that even though the water level come a very high level, the
dam still can accept it. Such a lot of concrete and steel make sure that the
dam is heavy and stable enough. The extremely large concrete and steel dam not
only can resist the huge force generated by water flow, but also can endure
thousands tons of explosive without total break.
By: Yue Cao
