Three Gorges Dam - Pushing the Limits: New Adventures in Engineering - page 141

After spending some time at the locks, we were driven over to the dam proper, which we viewed
head-on from its downriver side. The scale of this part of the project was even grander than that
of the locks, for it rose higher into the air and stretched over a kilometer wide before us. Under
construction to our left was the spillway, with one section of it raised to the dam's final height, giv-
ing a sense of how the finished structure would loom over this part of the river. To our right was
the power-plants section, which would hold fourteen hydraulic-turbine generator units capable of
generating 9,800 megawatts of power when this portion of the dam was completed. (The remaining
8,400 megawatt capacity will not be realized until the third stage of the project is completed and all
potential generating capacity is in place.)
Behind us stood the batch plant, where concrete was being mixed constantly for the twenty-four-
hour-a-day work schedule. One of the major considerations in placing concrete in such a massive
structure is how to dissipate the heat of hydration that is generated in the concrete as it cures. The
concrete, which experiences thermal contraction as it cools, can develop cracks. Taking the heat
away in a controlled and timely manner obviates this unwanted behavior. At the Three Gorges Dam,
the thermal problem was being handled in several ways. As with Hoover Dam, cooling pipes were
imbedded into the concrete to carry away some of the heat. A certain amount of undesirable heat
was itself eliminated at the source by mixing and placing the concrete at the lowest temperature
possible. This was accomplished through cooling the aggregate by blowing cold air over it, by us-
ing ice water in the mixing process, and by insuring that no concrete comes out of the batch plant at
over seven degrees Celsius. The measures appeared to be working. Only one significant crack had
appeared in the part of the dam in place, and the Chinese engineers seemed confident that it was
satisfactorily repaired.
After the dam itself and the tower cranes—red, white, and yellow— the next most prominent fea-
ture of the construction site was the conveyor-belt system that rose up to great heights on tempor-
ary concrete columns. The conveyor system to deliver the concrete was a critical component of the
job, for the rate at which concrete is placed largely determines if a project can be kept on schedule.
Unfortunately, shortly before our visit to the site, an accident involving one of the conveyors had
killed some workers. Before that accident, we were told, the safety record of the project had been
excellent. At the time of our visit, the conveyor system was not operating at the desired capacity,
which irritated the Chinese, and local papers were carrying stories of a lawsuit against the conveyor
company for breach of contract.
While at the construction site, it was hard not to be awed by the enormity of the project and the
confidence of the engineers working to hold back the legendary Yangtze, building on their exper-
ience with Gezhouba Dam and the many other flood-control and hydroelectric projects completed
throughout their country in recent decades. (A late-twentieth-century survey by the World Commis-
sion on Dams found that 46 percent of the world's forty-five thousand large dams were located in
China. It also reported that, although they have contributed significantly to human development,
dams have also been the cause of considerable social and environmental damage.)
The convincing official arguments that the Chinese put forth about the multifarious good that the
Three Gorges Dam will bring to their emerging economy impress visitors from a country that is
what it is today in part because its engineers also tamed great and scenic rivers like the Colorado and