In today’s world the technology has intensified to such a great extent and the construction industry is not left untouched with this.
The Three Gorges Dam is a pinnacle of dam engineering showing that the minds of people have broken all boundaries.
Built on the Yangtze river
Length- 2 Km
Height- 185 m (up to 60 stories high)
Construction period- 17 years ( 1993 to 2009)
Manpower – 40000 workers
Capacity- 20000 MW
Need for the dam
China required an enormous amount of power to feed its rapidly increasing population and its industrial sector. Also a solution to control the once in a decade flooding of the Yangtze river causing devastating damage to the country life and economy.
Let’s begin with what we are here for to see the challenges faced in the construction and the way they got over with it to build an example of great engineering.
Overcoming the challenges
Well said ” We should learn from our past mistakes to build a better future”. Over here you will see this came out to be true in case of the world’s largest dam.
Its not easy to build a structure so big without the hard working labor and great engineering minds. It was because of them that the problems faced while construction were solved. Below we will see some of the main Leaps made.
The technology for the power generation was taken from the Debdon Dam built in 18th century which used Thomson turbine to generate 4 MW of power.
The concept of Thomson turbine was taken to all new level . It consist 3 power houses with a total of 32 generators. The water is made to strike the turbine attached at the end of large concrete tubes which rotates the turbine and further the shaft of generator attached to the turbine producing enormous power.
- River control
Controlling the flow of the mighty Yangtze river was next to impossible. But the lessons learnt from the Mareges Dam, France built in 1914 gave the problem to the solution.
Two coffer dams were built from stone and one from concrete to isolate the area from the water so that the construction of the dam could take place. This resulted in rising of water level causing 150000 Acres of land being flooded hence millions of people from the surrounding area were rehabilitated which itself was a very tedious task.
After the completion of construction the other challenge was to blast the coffer dam safely without affecting the dam structure. This was the final test of the dam stability failure of which would have cause huge economic and life loss. 190 tonnes of dynamite was used to get this task in place.
- Building Material
Construction of the Hoover Dam in 1930 gave a lesson that using concrete has to be done very carefully as due to the large amount of difference in inner core and outer surface temperature while setting causes cracks to develop. Also the proper setting of concrete takes a lot of time due to the enormous amount being used.
In case of the Three Gorges Dam the problem was to keep concrete cool while setting even in the hot weather of china to prevent it from cracks being developed in it. To overcome this problem along with the large time taken for setting of concrete a huge cooling factory was developed in the dam structure which uses 950 Km in length of steel pipe through which the river water after cooling was passed so as to reduce the heat generated and setting time which would be 125 years if done traditionally to 22 months by this method.
Also the ingredients were cooled before being mixed to form concrete and a fog was created in the area where concrete was being poured to prevent from heat entering the concrete blocks.
Failure of the dam situated in Pennsylvania, U.S in 1889 posed great worries for the engineers of the world’s largest dam. The cause of failure was erosion of the river bed. There has to be a remarkable way out of the box to deal with this problem while constructing the Three Gorges dam.
The solution was adopted from the Grand Coulee Dam built in 1933 in which a concrete ramp was made at the bottom of the dam shooting down the water through the spillway water while dissipating its energy.
In the case of the Gorges Dam a ramp was made similar to the Grand Coulee dam the difference being the water was made to shoot the water into the air dropping 100m downstream breaking water into small droplets and loosing much of its energy.
- River navigation
The Yangtze river served as a major shipping route for goods and public transportation and taking them across was again an issue of great concern.
The technology was adopted from the Krasnoyarsk Dam which used hydraulics to lift the water and take ships across the dam on the guide rail. This concept was taken to a new level to take care of the heavy traffic ( 170 ships a day) served by the Yangtze river.
The biggest ship lock was build in the dam. The ships enter the bottom of the first block of the five blocks and the gates are closed to raise the water level and take the ship to next block. It took 4 hrs to cross the dam and was certainly not suitable for public ferry.
To solve the problem of public ferry an elevator like system was built which used 61000 tons of concrete blocks acting as counterweights attached to the steel trough by cables. It is capable of lifting weight of upto 3000 tons across its height of 113 m. As the weight was dropped the ship was lifted up and taken to other side of the dam.
- Silting of reservoir
Silting is a major problem of the reservoir caused due to settling of sediments and is huge in case of flood water ( upto 500 million tons per year equivalent to a 1 km cube). Also since all the sediments are settled in the reservoir the water reaching the agricultural land lacked nutrients which led to increased use of fertilizers.
To get away with such problems a way has to be developed to pass the sediments. For this sluice gates were made deep down the dam which were hydraulically lifted to a height of bus and allowing the settled sediments to pass. Still 30% – 60% of sediments remained in the reservoir.
A huge amount of money was invested for successful completion of the world’s largest dam which would serve China’s population for at least a 100 year without any problems faced making the investment a worth for value.
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