二級公路設計專業(yè)外文翻譯

1、本科畢業(yè)設計（論文）專業(yè)外文翻譯專業(yè)名稱：土木工程專業(yè)（道路與橋梁）年級班級：道橋08-5班學生姓名：宋鵬指導教師：廖明成河南理工大學土木工程學院二一二年五月十八日河南理工大學本科畢業(yè)設計 專業(yè)外文翻譯Geometric Design of HighwaysThe road is one kind of linear construction used for travel. It is made of the roadbed, the road surface, the bridge, the culvert and the tunnel. In addition, it also has

2、the crossing of lines, the protective project and the traffic engineering and the route facility.The roadbed is the base of road surface, road shoulder, side slope, side ditch foundations. It is stone material structure, which is designed according to route's plane position .The roadbed, as the

3、base of travel, must guarantee that it has the enough intensity and the stability that can prevent the water and other natural disaster from corroding.The road surface is the surface of road. It is single or complex structure built with mixture. The road surface require being smooth, having enough i

4、ntensity, good stability and anti-slippery function. The quality of road surface directly affects the safe, comfort and the traffic.Highway geometry designs to consider Highway Horizontal Alignment, Vertical Alignment two kinds of linear and cross-sectional composition of coordination, but also pay

5、attention to the smooth flow of the line of sight, etc. Determine the road geometry, consider the topography, surface features, rational use of land and environmental protection factors, to make full use of the highway geometric components of reasonable size and the linear combination.1.Alignment De

6、signThe alignment of a road is shown on the plane view and is a series of straight lines called tangents connected by circular. In modern practice it is common to interpose transition or spiral curves between tangents and circular curves.Alignment must be consistent. Sudden changes from flat to shar

7、p curves and long tangents followed by sharp curves must be avoided; otherwise, accident hazards will be created. Likewise, placing circular curves of different radii end to end (compound curves) or having a short tangent between two curves is poor practice unless suitable transitions between them a

8、re provided. Long, flat curves are preferable at all times, as they are pleasing in appearance and decrease possibility of future obsolescence. However, alignment without tangents is undesirable on two-lane roads because some drivers hesitate to pass on curves. Long, flat curves should be used for s

9、mall changes in direction, as short curves appear as “kink”. Also horizontal and vertical alignment must be considered together, not separately. For example, a sharp horizontal curve beginning near a crest can create a serious accident hazard.A vehicle traveling in a curved path is subject to centri

10、fugal force. This is balanced by an equal and opposite force developed through cannot exceed certain maximums, and these controls place limits on the sharpness of curves that can be used with a design speed. Usually the sharpness of a given circular curve is indicated by its radius. However, for ali

11、gnment design, sharpness is commonly expressed in terms of degree of curve, which is the central angle subtended by a 100-ft length of curve. Degree of curve is inversely proportional to the radius.Tangent sections of highways carry normal cross slope; curved sections are super elevated. Provision m

12、ust be made for gradual change from one to the other. This usually involves maintaining the center line of each individual roadway at profile grade while raising the outer edge and lowering the inner edge to produce the desired super elevation is attained some distance beyond the point of curve. If

13、a vehicle travels at high speed on a carefully restricted path made up of tangents connected by sharp circular curve, riding is extremely uncomfortable. As the car approaches a curve, super elevation begins and the vehicle is tilted inward, but the passenger must remain vertical since there is on ce

14、ntrifugal force requiring compensation. When the vehicle reaches the curve, full centrifugal force develops at once, and pulls the rider outward from his vertical position. To achieve a position of equilibrium he must force his body far inward. As the remaining super elevation takes effect, further

15、adjustment in position is required. This process is repeated in reverse order as the vehicle leaves the curve. When easement curves are introduced, the change in radius from infinity on the tangent to that of the circular curve is effected gradually so that centrifugal force also develops gradually.

16、 By careful application of super elevation along the spiral, a smooth and gradual application of centrifugal force can be had and the roughness avoided.Easement curves have been used by the railroads for many years, but their adoption by highway agencies has come only recently. This is understandabl

17、e. Railroad trains must follow the precise alignment of the tracks, and the discomfort described here can be avoided only by adopting easement curves. On the other hand, the motor-vehicle operator is free to alter his lateral position on the road and can provide his own easement curves by steering i

18、nto circular curves gradually. However, this weaving within a traffic lane (but sometimes into other lanes) is dangerous. Properly designed easement curves make weaving unnecessary. It is largely for safety reasons, then, that easement curves have been widely adopted by highway agencies.For the same

19、 radius circular curve, the addition of easement curves at the ends changes the location of the curve with relation to its tangents; hence the decision regarding their use should be made before the final location survey. They point of beginning of an ordinary circular curve is usually labeled the PC

20、 (point of curve) or BC (beginning of curve). Its end is marked the PT (point of tangent) or EC (end of curve). For curves that include easements, the common notation is, as stationing increases: TS (tangent to spiral), SC (spiral to circular curve), CS (circular curve to spiral), and ST (spiral go

21、tangent).On two-lane pavements provision of a wilder roadway is advisable on sharp curves. This will allow for such factors as (1) the tendency for drivers to shy away from the pavement edge, (2) increased effective transverse vehicle width because the front and rear wheels do not track, and (3) add

22、ed width because of the slanted position of the front of the vehicle to the roadway centerline. For 24-ft roadways, the added width is so small that it can be neglected. Only for 30mph design speeds and curves sharper than 22°does the added width reach 2 ft. For narrower pavements, however, wid

23、ening assumes importance even on fairly flat curves. Recommended amounts of and procedures for curve widening are given in Geometric Design for Highways.2. GradesThe vertical alignment of the roadway and its effect on the safe and economical operation of the motor vehicle constitute one of the most

24、important features of road design. The vertical alignment, which consists of a series of straight lines connected by vertical parabolic or circular curves, is known as the “grade line.” When the grade line is increasing from the horizontal it is known as a “plus grade,” and when it is decreasing fro

25、m the horizontal it is known as a “minus grade.” In analyzing grade and grade controls, the designer usually studies the effect of change in grade on the centerline profile.In the establishment of a grade, an ideal situation is one in which the cut is balanced against the fill without a great deal o

26、f borrow or an excess of cut to be wasted. All hauls should be downhill if possible and not too long. The grade should follow the general terrain and rise and fall in the direction of the existing drainage. In mountainous country the grade may be set to balance excavation against embankment as a clu

27、e toward least overall cost. In flat or prairie country it will be approximately parallel to the ground surface but sufficiently above it to allow surface drainage and, where necessary, to permit the wind to clear drifting snow. Where the road approaches or follows along streams, the height of the g

28、rade line may be dictated by the expected level of flood water. Under all conditions, smooth, flowing grade lines are preferable to choppy ones of many short straight sections connected with short vertical curves.Changes of grade from plus to minus should be placed in cuts, and changes from a minus

29、grade to a plus grade should be placed in fills. This will generally give a good design, and many times it will avoid the appearance of building hills and producing depressions contrary to the general existing contours of the land. Other considerations for determining the grade line may be of more i

30、mportance than the balancing of cuts and fills.Urban projects usually require a more detailed study of the controls and finer adjustment of elevations than do rural projects. It is often best to adjust the grade to meet existing conditions because of the additional expense of doing otherwise.In the

31、analysis of grade and grade control, one of the most important considerations is the effect of grades on the operating costs of the motor vehicle. An increase in gasoline consumption and a reduction in speed are apparent when grades are increase in gasoline consumption and a reduction in speed is ap

32、parent when grades are increased. An economical approach would be to balance the added annual cost of grade reduction against the added annual cost of vehicle operation without grade reduction. An accurate solution to the problem depends on the knowledge of traffic volume and type, which can be obta

33、ined only by means of a traffic survey.While maximum grades vary a great deal in various states, AASHTO recommendations make maximum grades dependent on design speed and topography. Present practice limits grades to 5 percent of a design speed of 70 mph. For a design speed of 30 mph, maximum grades

34、typically range from 7 to 12 percent, depending on topography. Wherever long sustained grades are used, the designer should not substantially exceed the critical length of grade without the provision of climbing lanes for slow-moving vehicles. Critical grade lengths vary from 1700 ft for a 3 percent

35、 grade to 500 ft for an 8 percent grade.Long sustained grades should be less than the maximum grade on any particular section of a highway. It is often preferred to break the long sustained uniform grade by placing steeper grades at the bottom and lightening the grade near the top of the ascent. Dip

36、s in the profile grade in which vehicles may be hidden from view should also be avoided. Maximum grade for highway is 9 percent. Standards setting minimum grades are of importance only when surface drainage is a problem as when water must be carried away in a gutter or roadside ditch. In such instan

37、ces the AASHTO suggests a minimum of 0.35%.3. Sight DistanceFor safe vehicle operation, highway must be designed to give drivers a sufficient distance or clear version ahead so that they can avoid unexpected obstacles and can pass slower vehicles without danger. Sight distance is the length of highw

38、ay visible ahead to the driver of a vehicle. The concept of safe sight distance has two facets: “stopping” (or “no passing”) and “passing”.At times large objects may drop into a roadway and will do serious damage to a motor vehicle that strikes them. Again a car or truck may be forced to stop in the

39、 traffic lane in the path of following vehicles. In dither instance, proper design requires that such hazards become visible at distances great enough that drivers can stop before hitting them. Further more, it is unsafe to assume that one oncoming vehicle may avoid trouble by leaving the lane in wh

40、ich it is traveling, for this might result in loss of control or collision with another vehicle.Stopping sight distance is made up of two elements. The first is the distance traveled after the obstruction comes into view but before the driver applies his brakes. During this period of perception and

41、reaction, the vehicle travels at its initial velocity. The second distance is consumed while the driver brakes the vehicle to a stop. The first of these two distances is dependent on the speed of the vehicle and the perception time and brake-reaction time of the operator. The second distance depends

42、 on the speed of the vehicle; the condition of brakes, times, and roadway surface; and the alignment and grade of the highway.On two-lane highways, opportunity to pass slow-moving vehicles must be provided at intervals. Otherwise capacity decreases and accidents increase as impatient drivers risk he

43、ad-on collisions by passing when it is unsafe to do so. The minimum distance ahead that must be clear to permit safe passing is called the passing sight distance. In deciding whether or not to pass another vehicle, the driver must weigh the clear distance available to him against the distance requir

44、ed to carry out the sequence of events that make up the passing maneuver. Among the factors that will influence his decision are the degree of caution that he exercises and the accelerating ability of his vehicle. Because humans differ markedly, passing practices, which depend largely on human judgm

45、ent and behavior rather than on the laws of mechanics, vary considerably among drivers. The geometric design is to ensure highway traffic safety foundation, the highway construction projects around the other highway on geometric design, therefore, in the geometry of the highway design process, if ap

46、pear any unsafe potential factors, or low levels of combination of design, will affect the whole highway geometric design quality, and the safety of the traffic to bring adverse impact. So, on the geometry of the highway design must be focus on.公路幾何設計公路是供汽車或其他車輛行駛的一種線形帶狀結構體。它是由路基、路面、橋梁、涵洞和隧道組成。此外，它還

47、有路線交叉、防護工程和交通工程及沿線設施。路基是路面、路肩、邊坡、邊溝等部分的基礎。它是按照路線的平面位置在地面上開挖和填筑成的土石料構造物。路基作為行車部分的基礎，必須保證它有足夠的強度和穩(wěn)定性，可以防止水及其他自然災害的侵蝕。路面是公路表面的部分。它是用混合料鋪筑的單層或多層結構物。路面要求光滑，具有足夠的強度，穩(wěn)定性好和抗?jié)窕δ?。路面質量的好環(huán)，直接影響到行車的安全性、舒適性和通行。公路幾何線形設計要考慮公路平面線形、縱斷面線形兩種線形以及橫斷面的組成相協(xié)調，還要注意視距的暢通等等。確定公路幾何線形時，在考慮地形、地物、土地的合理利用及環(huán)境保護因素時，要充分利用公路幾何組成部分的合理尺

48、寸和線形組合。1、線形設計道路的線形反映在平面圖上是由一系列的直線和與直線相連的圓曲線構成的。現(xiàn)代設計時常在直線與圓曲線之間插入緩和曲線。線形應是連續(xù)的，應避免平緩線形到小半徑曲線的突變或者長直線末端與小半徑曲線相連接的突然變化，否則會發(fā)生交通事故。同樣，不同半徑的圓弧首尾相接（曲線）或在兩半徑不同的圓弧之間插入短直線都是不良的線形，除非在圓弧之間插入緩和曲線。長而平緩的曲線在任何時候都是可取的，因為這種曲線線形優(yōu)美，將來也不會廢棄。然而，雙向道路線形全由曲線構成也是不理想的，因為一些駕駛員通過曲線路段時總是猶豫。長而緩的曲線應用在拐角較小的地方。如果采用短曲線，則會出現(xiàn)“扭結”。另外，線路的

49、平、縱斷面設計應綜合考慮，而不應只顧其一，不顧其二，例如，當平曲線的起點位于豎曲線的頂點附近時將會產生嚴重的交通事故。行駛在曲線路段上的車輛受到離心力的作用，就需要一個大小相同方向相反的由超高和側向磨擦提供的力抵消它，這些控制值對于某一規(guī)定設計車速可能采用曲線的曲率作了限制。通常情況下，某一圓曲線的曲率是由其半徑來體現(xiàn)的。而對于線形設計而言，曲率常常通過曲線的程度來描述，即100英尺長的曲線所對應的中心角，曲線的程度與曲線的半徑成反比。公路的直線地段設置正常的路拱，而曲線地段則設置超高，在正常斷面與超高斷面之間必須設置過渡漸變路段。通常的做法是維持道路每一條中線設計標高不變，通過抬高外側邊緣，

50、降低內側邊緣以形成所需的超高，對于直線與圓曲線直接相連的線形，超高應從未到達曲線之前的直線上開始，在曲線頂點另一端一定距離以外達到全部超高。如果車輛以高速度行駛在直線與小半徑的圓曲線相連的路段，行車是極不舒服。汽車駛近曲線路段時，超高開始，車輛向內側傾斜，但乘客須維持身體的垂直狀態(tài)，因為此時未受到離心力的作用。當汽車到達曲線路段時，離心力突然產生，迫使乘客向外傾斜，為了維持平衡，乘客必須迫使自己的身體向內側傾斜。由于剩余超高發(fā)揮作用，乘客須作進一步的姿勢的調整。當汽車離開曲線時，上述過程剛好相反。插入緩和曲線后，半徑從無窮大逐漸過渡到圓曲線上的某一固定值，離心力逐漸增大，沿緩和曲線心設置超高，

51、離心力平穩(wěn)逐漸增加，避免了行車顛簸。緩和曲線在鐵路上已經使用多年，但在公路上最近才得以應用，這是可以理解的。火車必須遵循精確的運行軌道，采用緩和曲線后，上述那種不舒服的感覺才能消除。然而，汽車司機在公路上可以隨意改變側向位置，通過迂迴進入圓曲線來為自己提供緩和曲線。但是在一個車道上（有時在其他車道上）做這種迂迴行駛是非常危險的。設計合理的緩和曲線使得上述迂迴沒有必要。主要是出于安全原因，公路部門廣泛采用了緩和曲線。對于半徑相同的圓曲線來說，在未端加上緩和曲線就會改變曲線與直線的相關位置，因此應在最終定線勘測之前應決定是否采用緩和曲線。一般曲線的起點標為PC或BC，終點標為PT或EC。對含有緩和曲線的曲線，通常的標記配置增為：TC、SC、CS和ST。對于雙向道路，急彎處應增加路面寬度，這主要基于以下因素：（1）駕駛員害怕駛出路面邊緣；（2）由于車輛前輪和后輪的行駛軌跡不同，車輛有效橫向寬度加大；（3）車輛前方相對于公路中線傾斜而增加的寬度。對于寬度為24英尺的道路，增加的寬度很小，可以忽略。只有當設計車速為30mile/h，且曲度大于22時，加寬可達2英尺。然而，對于較窄的路面，即使是在較平緩的曲線路段上，加寬也是很重要推薦加寬值及加寬設計見公路線形設計2、縱坡線