1、 外文翻译原文 Road DesignHistory of Road DesignFirstly let me apologise for this page. It is largely text based due to the nature of it and if reading is difficult then I am sorry. This is due solely to the material covered and is the only page in the series. This is not typical as the rest have graphics
2、or images to keep you amused. Secondly this page is very much a history of road building in the United KingdomThe first road builders of any significance in Western Europe were the Romans, who saw the ability to move quickly as essential for both military and civil reasons. It is from the Romans tha
3、t the term highway comes as all their roads were elevated 1m above the local level of the land. This was to minimise the risk of an ambush, as was the best known characteristic of the roads, their lack of corners. The standards set by the Romans in terms of durability far exceeded anything achieved
4、after the fall of the empire.The Roman approach to road design is essentially the same as that in current use. The roads were constructed of several different layers, increasing in strength from the bottom. The lowest layer was normally a rubble, intermediate layers were made of lime bound concrete
5、and the upper layer was a flag or lime grouted stone slabs. The thickness of the layers was varied according to the local ground conditions.After the fall of the Roman Empire the road system fell into a state of disrepair and by the end of the middle ages, there was in effect no road system in the c
6、ountry. The only routes available were unpaved tracks, muddy and impassable in winter and dusty and impassable in summer. Diversions around particularly poor stretches resulted in sinuous alignments. The state of the roads combined with the general lawlessness at the time meant only the determined o
7、r insane traveled. The first change in this attitude came in 1555 when an Act of Parliament was passed imposing a duty on all parishes to maintain its roads. Also included in the Act was the creation of the position of a Surveyor of Highways. This was unpaid and under resourced though and when combi
8、ned with the lack of technical skills it is no surprise that the post became distinctly unpopular and ineffective. This lack of resources meant that the first major road was not established until the latter part of the seventeenth century. These roads were known as turnpike roads where the road user
9、 paid a toll. The first sections were known as the Great North Road and has since become the A1 trunk road. In the following century Turnpike Trusts were established to provide turnpike roads along major routes in the United kingdom. In this improved financial climate roadbuilding techniques evolved
10、 thanks to the work of pioneers such as Telford and Macadam. By about 1830 a system of well paved built roads existed such that the only constraints on road traffic and travel times were imposed by the nature of road vehicles. The next improvement came about with the advent of the railways. With rap
11、id transport between towns now possible, the turnpikes became uneconomical and whilst roadbuilding in towns continued apace the turnpike trusts collapsed. Legislation in the late 19th century set the scene for the current administrative arrangements for highway construction and maintenance but the t
12、echnology remained primitive and empirical. Only in recent years has that situation improved to any extent and even now most road design is based on empirical relationships and experimental work.The present situation is almost a complete reversal, with funding for new roads coming from the private s
13、ector. In exchange for building and maintaining the road the owners are paid a toll by the government for each vehicle using the road, a sort of modern turnpike system.Traffic Analysis Road loading takes many different forms, from a bicycle to multi-axled truck and trailer combinations. Traffic Anal
14、ysis can be split into two well defined areas: Traffic Volume - This is the role of the Traffic Engineer and does not normally concern the Civil Engineer. This is not relevant to determining the load on the road, only the size and layout. Traffic Loading - This is the role of the Pavement Engineer a
15、nd involves determining the loading on the road to be carried forward to the Pavement Design. Traffic VolumeThe role of the traffic engineer is to enable all traffic to travel on the road at a reasonable speed and with an appropriate degree of safety. This is not the loading that is used in the Pave
16、ment Design. These values are used to determine the road width only. With relation to the volume of traffic using the road, the passenger car is adopted as the standard unit and other vehicles are assessed in terms of passenger car units (pcu).Differences in the urban and rural situations arise due
17、to the variation of speeds in the two areas. Decisions on road width are not normally made on total traffic flow per day as this is misleading but rather on the peak hourly flow. In Britain the maximum permissible flow is 3,000 pcu/h for a two lane dual carriageway and 4,500 pcu/h for a three lane d
18、ual carriageway (motorway). For all purpose roads with junctions these figures reduce to 1,100 and 1,900 pcu/h respectively. Where the road is new, studies must be carried out to estimate the volume of traffic expected to use the road. Where the new road replaces existing roads this is not too diffi
19、cult. If however the road is expected to change the flow of traffic then analysis should be carried out as to the volume and constitution of traffic on the new road. Matters are further complicated if the road is very long or provides access to or from a large town. Computer methods are now availabl
20、e to aid in this process. The constitution of traffic on the new road is of interest to the pavement engineer.Traffic LoadingIn this section, we will discuss the traffic loading that is taken forward to the pavement design section. Unlike in the above section where Passenger Car Units were the refer
21、ence unit, we will work in Standard Axles. This is a reference unit to determine the average loading on a pavement by what is known as the standard axle. This then allows a total loading over the life of the pavement to be determined, normally in Millions of Standard Axles (msa).EarthworksThe Proces
22、s of earthworks is to excavate the existing land to a suitable level so that road construction may begin. The earthworks can take the form of either excavation in the form of cuts or the construction of embankments to carry an elevated highway. Normally in a road design project, both will be necessa
23、ry and movement of earth from one part of the site to the next will be necessary. This should be done with as little waste created or as little extra material required as disposal or collection is expensive.Also included under the topic of earthworks is the compaction of the road materials to the ap
24、propriate level. This however is not covered as it is more concerned with the actual construction of the road than the design of it.This page is concerned solely with the design of the earthworks and not with the actual design of the embankments or cuts. If you wish to learn more about this then lin
25、ks to relevant pages are contained in the geotechnical section of the links page. A link to this can be found opposite.Of the topics covered in this page, they can be split up into the design of the earthworks and the plant used in the construction.ExcavationThe most important feature of the excavat
26、ion is the material you are working with. This will be known from the Site Investigation. Poor information can lead to technical problems and to cost overruns.There are many ways of classifying the soil in terms of its ease of excavation including seismic techniques. The most common in the United Ki
27、ngdom at present however is the Ease of Digging scale or diggability. This classifies the soil in one of four categories: E Easy digging - Loose free running soils eg sands, fine gravels. M Medium - Denser cohesive soils eg clayey gravel, low PI clays .M-H Medium to Hard - eg broken rock, wet heavy
28、clay, gravel with boulders. H Hard - material requiring blasting and hard high PI clays.Typical diggability factors can be seen in Table 1 below.Another important feature of rock is the amount of fissuring. There are two methods of assessing this, the percentage Rock Quality Data method and the Spac
29、ing of joints method. Each of these leads directly to an estimate of the uniaxial compressive strength and thus an indication of the excavation method. Both these can be found in the Manual of contracts document, Series 6001.Excavation increases the volume of material. It is therefore necessary to u
30、se a bulking factor to determine the volume of material that will be created by excavation. Bulking factor is defined as: Bulking Factor = Volume after Excavation/Volume before ExcavationSimilarly a shrinkage factor is defined for the compaction of a soil at its final destination.: Shrinkage Factor
31、= Volume after Compaction/Volume before ExcavationIn addition to the above properties, it is important to have some idea about the trafficability of the soils. This is because the excavation plant will need to drive over the soils without becoming bogged down. The trafficability of the soils is rela
32、ted to their drainage properties. Sands/Gravels Free Draining. Tend to have few problems. High PI Clays Low permeability will prevent water ingress so the surface becomes dangerous but not in the long term. Silts/Low PI Clays These cause the most problems. Permeability allows ingress which softens t
33、he soils thus weakening them.Asphalt Paving OperationIntroductionThe subject of this term project was an asphalt paving process utilizing a paving machine and 20 tons capacity tri-axle trucks. The location of the process was at the corner of Main and Madison in Greenwood ( South of Indianapolis ). T
34、he project is being run by the Reith-Riley Construction Company. - Indianapolis. The overall process involved : 1.Hot-mix batch plant cycle 2.Tri-axle truck cycle 3.Roller cycle 4.Spreader cycle 5.Crew cycle Because of the complexity of the overall construction process, we chose to observe, report o
35、n, analyze and model the paving process on the base layer of the 15 lane road. At that time, the other lane of the road was not paved yet. The road has slightly increasing grade and curve along the process. The preliminary process of gathering the data used in this project, the efficiency of the ope
36、ration, a model and MicroCYCLONE simulation of the process, and illustrations will be discussed and presented. Asphalt has been used by man for its adhesive and waterproofing properties. Asphalt was used in 3800 B.C. in the Euphrates and 2500 B.C. in Egypt. The Sumerians used asphalt in 6000 B.C. fo
37、r its shipbuilding industry. Today, asphalt is applied to roofing, sealants, caulking, brake linings, paints, enamels, and most widely used in the paving industry (Asphalt - Science and Technology, 1968). Process DescriptionBatch Plant ProductionFirst, aggregate travels through the cold feed bins, w
38、here initial proportioning of the aggregate takes place. The quantity of material leaving each bin is regulated by the size of the gate opening, or the speed of a belt, or a combination of the two. The aggregate is sent to a drier. Here the moisture is removed and is heated to provide the proper mix
39、ing temperature in the pugmill. The aggregate continues to the hot elevator by screens to the hot bins. The screens provide the final separation of the aggregate. The different sizes of aggregate are released into the weight hopper one bin at a time. The aggregate is dropped into the pugmill for mix
40、ing with the asphalt. The mixture is then dropped into a waiting truck or moved to a storage silo. Samples are taken from each hot bin for testing. A sieve analysis is conducted as well as gradation test. From the gradation information, the weight of the aggregate must be equal to the design gradati
41、on. A trial run should be performed and the weights adjusted until the desired mix is produced. (U.S. Department of Transportation, December 1984)The different sizes of aggregate are released into the weight hopper one bin at a time. The aggregate is dropped into the pugmill for mixing with the asph
42、alt. The mixture is then dropped into a waiting truck or moved to a storage silo. Samples are taken from each hot bin for testing. A sieve analysis is conducted as well as gradation test. From the gradation information, the weight of the aggregate must be equal to the design gradation. A trial run s
43、hould be performed and the weights adjusted until the desired mix is produced. (U.S. Department of Transportation, December 1984)Placing Asphalt PavementPlacing the Coat Before the paving operation starts, an asphalt distributor is used to spray asphalt on the unpaved surface. This film of asphalt s
44、erves as the prime and tact coats. The coats are then allowed to cure before the actual paving resume. The purpose of having these coats is to prevent any slippage between the surface and overlay during or after the compaction. (The Asphalt Institute) Placing the Asphalt Mix To start the paving oper
45、ation, the paver is positioned properly onto the road. The screed of the paver is lowered onto block of the same depth of the loose asphalt mat that is going to be laid on the road. (The screed is responsible for the setting the depth of the asphalt mix.) After that, the block can be removed and pav
46、ing can start. As soon as the haul truck arrives at the job site, the paving inspector must check that the asphalt delivered must be in a satisfactory condition. The paving inspector usually check for these criteria listed below: 1.blue smoke - blue smoke indicate that the mix is too hot. 2.stiff ap
47、pearance 3.mix slumped in truck. 4.lean, dull appearance - this indicates that the mix has insufficient asphalt. 5.rising steam - too much moisture. 6.segregation. 7.contamination. If there is any of the signs above is observed, the mix will be sent back to the batch plant to be reprocessed. After a
48、ll conditions are satisfied, the haul truck can load the mix into the receiving hopper of the paver. When loading the mix into the receiving hopper, the haul truck is placed carefully in front of the paver. The rear wheels of the truck should be in contact with the truck roller of the paver to avoid
49、 any misalignment with the paver. The paver will push the truck forwards as it paves the road. If skewness happens, the whole process will be delayed because they have to reposition the truck in front of the paver. Most paver used are self-propelled paver. Each of them consists of two main units: Tractor unit. -it includes the receiving hopper, slot conveyor, flow control gates, spreading crew, power plant, transm
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