1、交通系统交通运输一直是土木工程最重要的一个方面。古罗马工程师的巨大成就之一就是公路系统，它使罗马与帝国的各个省之间的快速交通成为可能。在工程方面的第一所培训学校就是桥梁和公路学校，它于1747年创建于法国。而在英国，一位道路建筑家，托马斯泰尔福特于1820年担任了土木工程学会的第一任主席。现代公路仍然根据18世纪及19世纪初法国人皮埃尔特埃萨凯，英国人泰尔福特，以及苏格兰人约翰L马克当所制定的原则进行建造。这些人设计出了最初的现代道路，这种道路具有坚实的垫层，基础就建在垫层的上面。他们设计的道路还具有排水良好而且不渗水的磨耗层，即直接承受车辆交通磨耗的表层。特埃萨凯和泰尔福特均采用较厚的石头基
2、础，在其上面铺筑由较小碎石组成的基层和由更小的石头组成的磨耗层。他们的道路还微微隆起成曲线，形成路拱和反拱以便使雨水流走。马克当认识到当土壤被夯实或压紧之后，只要保证干燥，其本身就可承受道路的重量，因而他能够通过在压实的垫层上铺碎石基层来省掉建造石头基础所需要的昂贵费用。当时车辆的铁质车轮把表层石头碾压成连续的，较为平整的，更加不透水的表面。早19世纪，货车和客车都采用铁或钢制车轮，这种道路是适用的。当汽车在20世纪初出现之后，其橡胶轮胎毁坏了这种平整的路面。因此，就采用焦油或沥青掺拌碎石，使路面表层更坚固的黏合一起。现在，遍布全世界的数百万公里的道路采用这种路面。在20世纪，道路建设基本上仅
3、在两方面进行了改进。第一种改进是采用混凝土作为磨耗层。另一种改进则是交通工程，即设计高速的大交通量的、造价经济并且对于车辆和旅客都安全的公路。交通工程已建成了现代高速公路，这种公路具有限定的入口和最安全的管理。老式道路常用的拐角形交叉已不使用，而采用互通式立体交叉或其他更为复杂的设计。现代高速公路通常设有专门的车道，在那里当车辆要驶出公路时可减速驶入时可加速。应该尽量减少急弯或陡坡，以使能在不减速的情况下连续行驶。由于单调已被实践证明是对安全有害的，故交通工程甚至要包括道路两旁景观的设计工作。当开始建设一条新的公路时，被称为推土机的大型运土机械要沿着指定路线平整土地。平土和填土的运土量都要预先
4、计算出来。不论在哪里，都要尽可能使移除土壤的挖方量等于就近所需的填方量。远距离运土是很昂贵的，而经济效益是工程师工作的一个关键方面。在运完土方并根据道路设计的横断面定形之后，其他机械就为垫层做准备。其中最主要的一种机械很可能是振动压路机，它被用来压实地面，直至地面能承受将要压在其上的基层及磨耗层传来的重量。但是在许多情况下，必须用其他材料与土拌和而使土壤稳定。这种材料可以是沥青，也可以是混凝土浆或者其他物质。接着是基层，它或者是碎石，或者是用一种稀薄的混凝土铺成，然后才铺磨耗层。磨耗层可以是一层沥青，也可以是一排排钢筋混凝土板。混凝土路面必须分段铺设，每段之间留有膨胀缝，使其能在不同气候条件下
5、膨胀和收缩。铺钢筋混凝土磨耗层的一种方法是在浇筑一部份混凝土之后，再铺钢筋，钢筋通常为格栅状或网栅状。为了保证良好的粘结，必须在浇筑完底部的后20分钟之内浇完顶层。另一种方法是先浇筑全部所需厚度的混凝土，然后再将钢筋网按预定的标高压到混凝土当中。一组总称为混凝土铺路机组的机器通常能以每分钟四分之三米的速度完成所有的工序。一种新的，称为滑膜铺路机的单机，除了不能铺设钢筋网外，可以完成混凝土铺路机组所能完成的所有工作。已经研究出了一种新技术，就是先把钢筋网安放就位，然后使机械通过并在钢筋周围浇筑混凝土。滑膜铺路机能以每分钟大约两米的速度进行工作。飞机场跑道的施工也按类似的步骤进行，只不过跑道用的水
6、泥板比公路用的要宽的多。飞机场必须设计的不仅能够承受大型喷气飞机的巨大荷载，而且还要能够承受发动机喷出的强烈的热流。飞机的冲击系数也不比汽车的大。公路与飞机场跑道的区别在于尺寸和强度，而不是设计和施工的方法。如果说大型混凝土高速公路是本世纪的交通奇迹的话，那么铁路就是19世纪的交通奇迹。在1829发明蒸汽机车以前，人们也知道运用铁路运输。不过，当时铁路线路的长度只限于马或者其他动物能够拖着重物进行短距离运输的范围内。这种铁路大部分是和采矿作业一起兴建起来的。在蒸汽机车成为使用机器之后，建造铁路的热潮迅速兴起，使铁路网络扩展到世界各地。到1920年，铁路建设的鼎盛时期已经基本结束。随着汽车的使用
7、日益广泛，重点就转移到公路建设上。除了有限的改进，诸如电气化等铁路已不再被人们重视。不过，现在人们对铁路又有了新的认识。例如，日本人最近开通了从东京到大阪的新干线，其高速列车在正常运行时，平均速度为每小时166公里，并且达到了最高速度为每小时210公里。甚至在许多铁路都处于不景气状况的美国，特别是在其东部地区，对提供良好服务的兴趣也正在增长。不仅在美国，而且在其他国家的人们对建立城市快速交通系统也呈现的较大的兴趣。附件2：外文原文（复印件）Transportation SystemsTransportation has always been one of the most important
8、 aspects of civil engineering .one of the great accomplishments of the Roman engineers was the highway system that made rapid communication possible between Rome and the provinces of the empire. The first school that offered training specifically in engineering was the School of Bridges and Highways
9、, established in France in 1747. And in England, Thomas Telford, a roadbuilder, became the first president of the Institution of Civil Engineers in 1820.Modern highways are still built according to the principles laid down in the eighteenth and early nineteenth cenruries by a Frenchman, Pierre Tresa
10、guet, the Englishman Telford, and a Scot, John L. McAdam. These men designed the first modern roads that had a firm footing, the surface on which the foundstion rested. Their roads also included good drainage and a wearing surface-the top levelthat directly receives the wear of traffic-that could no
11、t be penetratated by water. Both Tresaguet and Telford used a heavy foundation of stones, on top of which a base course of lighter crushed stones and a wearing surface of still smaller stones were built up. Their roads were also slightly curved in a crown or camber so that the water would run off. M
12、cAdam realized that the soil utself could bear the weight of the road when it was compacted or pressed down, aslong as it remained dry. He wasable therefore to eliminate the heavy cost of the stone foundation by laying a base course of crushed stone on top of a compacted footing. The iron wheels of
13、the carriages of his day ground the stones of the top level into a continually smoother and more watertight surface.These roads were adequate during the nineteenth century when wagons and carriages had tires made of iron or steel. When the automobile appeared at the beginng of the twentieth century,
14、 however, its rubber tires broke up the smooth surfaces. Therefore,the top layer was bound together more firmly by mixing the crushed rock with tar or asphalt. Millions of kilometers of roads throughout the world today have this kind of surface.Basically, roadbuilding has improved in only two ways i
15、n the twentieeh century. The first improvement involves the use of concrete for the wearing surface. The other is traffic engineering, the design of highways for high-speed, heavy-volume traffic, highways thathat are economical to build and safe for vehicles and their passengers. Traffic engineering
16、 has produced the modern express highway that has only limited access and maximum safety controls. The angular intersections common on older roads have been eliminated in favor of interchanges or others with even more complicated designs. Modern express highways usually have special lanes where traf
17、fic can either slow down before exiting or speed up upon entering.Extreme curves or steep slopes are minimiced so that the traffic can continue to move without slo wing down. Since monotony has proved to be a safety hacard, tiaffic engineering even includes the landscaping of the borders of the road
18、.When construction on a new highway begins, huge earthmoving machines called bulldocers level the ground along the designated route. The amount of earth to be moved, both in leveling and filling , has been previously calculated. Wherever possible, the amount in a cat where earth is being removed sho
19、ule be equlal to the amount needed for a nearby fill. Moving earth form a distant point is extremely expensive, and economy is a critical aspect of an engineers work.After the earth has been moved and shaped according to the design of the road, other machines prepare the footing . The most important
20、 of these is probably a vibrating roller, which compacts the earth until it can bear the weight of the base course ang wearing surface that will rest on it. In many cases, however, the soil must be stabilized by mixing some other material with it. This may be bitumen or a grout of concrete or some o
21、ther substance.The base course, which is made of either crushed stone or a layer of thinly-mixed concrete, comes next, the wearing surface, which may be a layer of asphalt or a series of reinforced concrete slabs, is then laid. A concrete surface be laid in segments separated by joints to allow for
22、expansion and contraction under difffering weather conditions. One method of laying a reinforced concrete wearing surface is to put down the steel rods, usually in the form of a grill or mesh, after a certain proportion of the concrete has been poured. The top level must be poured within twenty minu
23、tes of the pouring of the bottom level to assure proper bonding. Anther method is to pour the entire thickness of concrete and then force the steel mesh down into it to a predetermined level. A group of machines collectively callled a concrete train usually perform these operations at a rate of abou
24、t three-fourths of a meter per minute. A single new machine called a slipform pawer can perform all the different jobs of a concrete train excep laying the reinforcing mesh. However, a technique has been worked out in which the mesh is held in place before the machine passes over it and pours concre
25、te aroung it . The slipform paver can operate at a rate of about two meters per minute. The construction of airport runways follows similar procedures, except that the slabs in a runway are much wider then those in a highway. Airport runways must also be designed to carry the heavy load of the big m
26、odern jumbo jets, as well as to withstanf enormous blastes of heat from the engines of heat form the engines of the aircraft.The impact fatcor is also greater with airplanes than with automobiles. Highways differ form airport runways, however, insize and strength rather than design and construction
27、methods.If huge concrete freeways are the transportation phenomenon of hort this century, then the railroads were the transportation phenomenon of the nineteenth century . Transportation by rail was not unkonw before the invention of steam locomotive in 1892, but rail lines had been limited to the s
28、hort distances over which horses or other draft animals pulled the load. Most of the lines were bugreat ilt in conjunction with mining operations. After the steam locomotive became a practical machine, a surge of railroad construction rapidly spread a network of railroads across the face of the word
29、.By 1920 the age of railroad building generally seemed to be over. As automobiles came into increasingly wider use, the emphasis shifted to highway consruction. Except for few improvements such as electrification, railroads were neglected. Now, however, there is a renewed interest in railroads. The
30、Japanese for example, have recently opened the Tokaido line between Tokyo and Osaka, with express trains that average 166 kilometers per hiur and reach speeds as high as 210 kilometers per hour in nirmal operation. Even in the United Stares where many of the railroads are in deplorable condition, especially in the eastern part of rhe country, there is an increased in providing better service. There is also considerable interest-not only in the United States but in many other countries as well-in urban rapid transit systems. .此处忽略！- 9 -
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