资料简介： Bridge construction% J' ^/ P0 S( H7 G% }
Bridge construction can present extraordinary difficulties. Usually the foundations for the piers must rest on the bedrock, and often under water. One technique for working in these conditions is by means of a cofferdam. Piles usually made of interlocking steel plates are driven into the water bed. The water is then pumped out from within the area that has been enclosed.- T3 p7 m0 i6 N
Another technique is the use of the pneumatic caisson. The caisson is huge cylinder with a bottom edge that can cut into the water bed.. When compressed air is pumped into it, the water is forced out. Caissons must be used with extreme care. For one thing, workers can only stay in the compression chamber for short periods of time. For another, if they come up to normal atmospheric pressure too rapidly, they are subject to the bends, or caisson disease as it is also called, which is a crippling or even fatal condition caused by excess under construction between 1867 and 1874, at a time when the danger of working in compressed air was not fully understood, fourteen deaths were caused by the bends.% l J! O5 x6 N* E8 k$ W
桥梁建设
( t; n+ ]+ i- U1 V# }* T 桥建设在目前有一定的困难。 通常桩的基础必须放在基岩上而岩石经常在水下。 在这些环境条件里起作用的一种技术是通过一个围堰。 由钢板的做成的围堰被敲进含水层。 水从围堰里被抽出。
' H: d: ^- W+ J- i 另一种技术是使用气压沉箱。 沉箱是有巨大刃脚的圆筒，它能够进入河床。 当压缩的空气被泵送入它时，水被排挤出。在应用沉箱的过程必须非常小心。 原因之一，工人只能呆在里面非常短时间。 对于另一个来说如果他们太快的达到正常的大气压， 他们受到非常大的压强，容易得潜水病 也当时也叫沉箱病，有时甚至是致命的。这是由于血管中溶于过多的氮引起的的。在1867 和1874之间在桥梁的建设中， 当在压缩的空气里工作的危险没被完全了解时，有14起死亡事故是由这种原因引起的 。
| 
