篇篇学之4：The Arch Dams

There are three mainly types of dams: gravity dams,embankment dams and arch dams.(Considering these dams are ordinarily,we just take these for example.),Here we just describe the arch dam.
NO3.Arch dams
The arch dam is a curved dam which is dependent upon arch action for its strength.The arch dam is thinner and therefore require less material than any other type of dams.The arch dam is good for sites that are narrow and have strong abutments.The main force of a arch dams are as follows:force of the reservoir water,weight of concrete and forces together.There are other forces that may act on an arch dam:internal water pressure,temperature variations in the concrete earthquake loads.and settlement of the foundation or abutments.

Words:
gravity dam 重力坝 embankment dam 堤坝（土石坝） arch dam 拱坝 curve 曲面的
abutment 连接（拱肩） variate 变化 settlement 沉降