毕业论文（外文翻译）（2012届）学院名称土木与水利工程学院专业（班级）土木工程七班姓名（学号）李小润（20083650）指导教师扈惠敏系（教研室）负责人方诗圣PavementHighway pavements are divided into two main categories: rigitand flexible.The wearing surfaceof a rigid pavement is usually constructed of Portland cement concrete such that it acts like a beam over any irregularities in the underlying supporting material.The wearing surface of flexible pavements, on the other hand, is usually constructed of bituminous material such that they remain in contact with the underlying material even when minor irregularities occur.Flexible pavements usually consist of a bituminous surface underlaid with a layer of granular material and a layer of a suitable mixture of coarse and fine materials.Coarse aggregatesFine aggregatesTraffic loads are transferred by the wearing surface to the underlying supporting materials through the interlocking of aggregates, the frictionaleffect of the granular materials, and the cohesion of the fine materials.Flexible pavements are further divided into three subgroups: high type, intermediate type, and low type. High-type pavements have wearing surfaces that adequately support the expected traffic load without visible distress due to fatigue and are not susceptible to weather conditions.Intermediate-type pavements have wearing surfaces that range from surface treated to those with qualities just below that of high-type pavements. Low-type pavements are used mainly for low-cost roads and have wearing surfaces that range from untreated to loose natural materials to surface-treated earth.✹The components of a flexible pavement include the subgradeor prepared roadbed, the subbase, basecourse, and the surface course (Fig.11.1).✹Upper surface courseMiddle surface courseLower surface courseThe performance of the pavement depends on the satisfactory performance of each component, which requires proper evaluation of the properties of each component separately.✹The subgrade is usually the natural material located along the horizontal alignment of the pavement and serves as the foundation of the pavement structure.✹The subgrademay also consist of a layer of selected borrow materials, well compacted to prescribedspecifications.✹Compacting plantCompaction deviceCompactnessIt may be necessary to treat the subgrade material to achieve certain strength properties required for the type of pavement being constructed.Located immediately above the subgrade, the subbase component consists of a superior quality to that which generally is used for subgrade construction. The requirements for subbase materials are usually given in terms of the gradation, plastic characteristics, and strength. When the quality of the subgrade material meets the requirements of the subbase material, the subbase component may be omitted.In cases where suitable subbase material is not readily available ,the available material can be treated with other materials to achieve the necessary properties. This process of treating soils to improve their engineering properties is know as stabilization.✹The base course lies immediately above the subbase. It is placed immediately above the subgrade if a subbase course is not used.✹This course usually consists of granular materials such as crushed stone, crushed or uncrushed.The specifications for base course materials usually include stricter requirements than those for subbase materials, particularly with respect to their plasticity, gradation, and strength.Materials that do not have the required properties can be used as base materials if they are properly stabilized with Portland cement, asphalt, or lime .In some cases, high-quality base course materials may also be treated with asphalt or Portland cement to improve the stiffness characteristics of heavy-duty pavementsThe surface course is the upper course of the road pavement and is constructed immediately above the base course. The surface course in flexible pavement usually consists of a mixture of mineral aggregates and asphaltic materials.It should be capable of withstanding high tire pressures, resisting the abrasive forces due to traffic, providing a skid-resistant driving surface, and preventing the penetration of surface water into the underlying layers.✹The thickness of the wearing surface can vary from 3 in. to more than 6 in.（inch，英寸，2.54cm）, depending on the expected traffic on the pavement.It was shown that the quality of the surface course of a flexible pavement depends on the mix design of the asphalt concrete used.✹Rigid highway pavements usually are constructed to carry heavy traffic loads, although they have been used for residential and local roads. Properly designed and constructed rigid pavements have long service lives and usually are less expensive to maintain than the flexible pavements.✹The Portland cement concrete commonly used for rigid pavements consists of Portland cement, coarse aggregate, fine aggregate, and water. Steel reinforcing rods may or may not be used, depending on the type of pavement being constructed.Rigid highway pavements be divided into three general type: plain concrete pavements, simply reinforced concrete pavements, and continuously reinforced concrete pavement. The definition of each pavement type is related to the amount of reinforcement used.Plain concrete pavement has no temperature steel or dowels for load transfer.However, steel tie bars are often used to provide a hingeeffect at longitudinal joints and to prevent the opening of these joints. Plain concrete pavements are used mainly on low-volume highways or when cement-stabilized soils are used as subbase.Joints are placed at relatively shorter distances (10 to 20 ft) than with the other types of concrete pavements to reduce the amount of cracking.In some case, the transverse joints of plain concrete pavements are skewed about 4 to 5 ft in plan, such that only one wheel of a vehicle passes through the joint at a time. This helps to provide a smoother ride.Simply reinforced concrete pavements have dowels for the transfer of traffic loads across joints, with these joints spaced at larger distances, ranging from 30 to 100 ft. Temperature steel is used throughout the slab, with the amount dependent on the length of the slab. Tie bars are also commonly used in longitudinal joints.Continuously reinforced concrete pavements have no transverse joints, except construction joints or expansion joints when they are necessary at specific positions, such as at bridges.These pavements have a relatively high percentage of steel, with the minimum usually at 0.6 percent of the cross section of the slab. They also contain tie bars across the longitudinal joints.h/2h/25~10cm填缝料 横向施工缝构造填缝料平缝加拉杆型Bituminous Surface CoursesThe bituminous surface course has to provide resistance to the effects of repeated loading by tyres and to the effects of the environment.✹In addition, it must offer adequate skid resistance in wet weather as well as comfortable vehicle ride. It must also be resistant to rutting and to cracking.✹It is also desirable that surface course is impermeable, except in the case of porous asphalt.Hot rolled asphalt (HRA) is a gapgraded material with less coarse aggregate. In fact it is essentially a bitumen/fine aggregate/filler mortar into which some coarse aggregate is placed.The mechanical propertiesare dominated by those of the mortar. This material has been extensively used as the wearing course on major road in the UK, though its use has recently declined as new materials have been introduced.✹It provides a durablelayer with good resistance to cracking and one which is relatively easy to compact. The coarse aggregate content is low (typically 30%) which results in the compacted mixture having a smooth surface. Accordingly, the skid resistance is inadequate and precoated chippings are rolled into the surface at the time of laying to correct this deficiency.In Scotland, HRA wearing course remains the preferred wearing course on trunk roads including motorway but，since 1999 thin surfacings have been the preferred option in England and Wales. Since 1999 in Northern Ireland, HRA wearing course and thin surfacings are the preferred permitted options.Porous asphalt (PA) is a uniformly graded material which is designed to provide large air voids so that water can drain to the verges within the layer thickness. If the wearing course is to be effective, the basecourse below must be waterproof and the PA must have the ability to retain its open textured properties with time.Thick binder films are required to resist water damage and ageing of the binder. In use, this material minimizes vehicle spray, provides a quiet ride and lower rolling resistance to traffic than dense mixtures.✹It is often specified for environmental reasons but stone mastic asphalt (SMA) and special thin surfacings are generally favoured in current UK practice.There have been high profile instances where a PA wearing course has failed early in its life. The Highways Agency does not recommend the use of a PA at traffic levels above 6000 commercial vehicles per day.✹Asphaltic concrete and dense bitumen macadam (DBM) are continuously graded mixtures similar in principle to the DBMs used in roadbases and basecourses but with smaller maximum particle sizes. Asphaltic concrete tends to have a slightlydenser grading and is used for road surfaces throughout the world with the excepting of the UK.✹It is more difficult to meet UK skid resistance Standards with DBMs than HRA, SMA or PA. This problem can be resolves by providing a separate surface treatment but doing so generally makes DBM economically unattractive.✹Stone mastic asphalt (SMA) material was pioneeredin Germany and Scandinavia and is now widely used in the UK. SMA has a coarse, aggregrate skeleton, like PA, but the voids are filled with a fine aggregate/filler /bitumen mortar.✹In mixtures using penetration grade bitumen , fibres are added to hold the bitumen within the mixture (to prevent “binder drainage”).Bitumen✹oil bitumen( earth oil)✹natural bitumen✹TarWhere a polymer modified bitumen is used, there is generally no need for fibres. SMA is a gap-graded material with good resistance to rutting and high durability. modified bitumen✹SBS✹SBR✹PE\EV A✹It differs from HRA in that the mortar is designed to just fill the voids in the coarse aggregate whereas, in HRA, coarse aggregate is introduced into the mortar and does not provide a continous stone matrix. The higher stone content HRAs ,however, are rather similar to SMA but are not wide used as wearing courses in the UK, being preferred for roadbase and basecourse construction.A variety of thin and what were called ultra thin surfacings (nowadays, the tendency is to use the term ‘thin surfacings’ for both thin and ultra thin surfacings ) have been introduced in recent years, principally as a result of development work concentrated in France.These materials vary in their detailed constituents but usually have an aggregate grading similar to SMA and often incorporate a polymer modified bitumen.They may be used over a high stiffness roadbase and basecourse or used for resurfacing of existing pavements. For heavy duty pavements (i .e those designed to have a useful life of forty years), the maintenance philosophy is one of minimum lane occupancy, which only allows time for replacement of the wearing course to these ‘long life’ pavement structures. The new generation of th in surfacings allows this to be conveniently achieved.The various generic mixture types described above can be compared with respect to their mechanical properties and durability characteristics by reference to Fig.12.1. This shows, in principle, how low stone content HRA, asphaltic concrete, SMA and PA mixtures mobilize resistance to loading by traffic.Asphaltic concrete (Fig.12.1a)) presents something of a compromise when well designed, since the dense aggregate grading can offer good resistance to the shear stresses which cause rutting, while an adequate binder content will provide reasonable resistance to the tensile stresses which cause cracking.In general, the role of the aggregate dominates. DBMs tend to have less dense gradings and properties which, therefore, tend towards good rutting resistance andaway from good crack resistance.HRA (Fig.12.1b)) offers particularly good resistance to cracking through the binder rich mortar between the coarse aggregate particles. This also provides good durability but the lack of coarse aggregate content inhibits resistance to rutting.SMA and PA are shown in the same diagram ( Fig.c)) to emphasis the dominant role the coarse aggregate. In both case, well coated stone is used. In PA, the void space remains available for drainage of water, whilst in SMA, the space is occupied by a fine aggregate/ filler/ bitumen/ fibre mortar.Both materials offer good rutting resistance through the coarse aggregate content. The tensile strength of PA is low whilst that of SMA is probably adequate but little mechanical testing data have been reported to date.Drainage for Road and Airports✹Provision of adequate drainage is important factor in the location and geometric design of road and airports. Drainage facilities on any highway, street and airport should adequately provide for the flow of water away from the surface of the pavement to properly designed channels.Inadequate drainage will eventually result in serious damage to the structure.✹In addition, traffic may be slowed by accumulated water on the pavement, and accidents may occur as a result of hydroplaning and loss of visibility from splash and spray. The importance of adequate drainage is recognized in the amount of highway construction dollars allocated to drainage facilities. About25 percent of highway construction dollars are spent for erosion control anddrainage structures, such as culverts, bridges, channels, and ditches.✹Highway Drainage Structures✹One of the main concerns of the highway engineer is to provide an adequate size structure, such that the waterway opening is sufficiently large to discharge the expected flow of water.Inadequately sized structures can result in water impounding, which may lead to failure of the adjacent sections of the highway due to embankments being submerged in water for long periods.✹The two general categories of drainage structures are major and minor. Major structures are those with clear spans greater than 20 feet, whereas minor structures are those with clear spans of 20 feet or less .✹Major structures are usually large bridges, although multiple-span culverts may also be included in this class. Minor structures include small bridges and culverts.Emphasis is placed on selecting the span and vertical clearancerequirements for major structures. The bridge deck should be located above the high water mark .The clearance above the high water mark depends on whether the waterway is navigable ✹If the waterway is navigable, the clearance above the high water mark should allow the largest ship using the channel to pass underneath the bridge without colliding with the bridge deck. The clearance height, type, and spacing of piers also depend on the probability of ice jams and the extentto which floating logs and debris appear on the waterway during high water.✹An examination of the banks on either side of the waterway will indicate the location of the high water mark, since this is usually associated with signs of erosion and debris deposits. Local residents, who have lived near and observed the waterway during flood stages over a number of years, can also give reliable information on the location of the high water mark. Stream gauges that have been installed in the waterway for many years can also provide data that can be used to locate the high water mark.Minor structures, consisting of short-span bridges and culverts, are the predominant type of drainage structures on highways. Although openings for these structures are not designed to be adequate for the worst flood conditions, they shouldbe large enough to accommodate the flow conditions that might occur during the normal life expectancy of the structure.✹Provision should also be made for preventing clogging of the structure due to floating debris and large boulders rolling from the banks of steep channels.✹Culverts are made of different materials and in different shapes. Materials used to construct culverts include concrete（reinforced and unreinforced）, corrugated steel, and corrugatedaluminum. Other materials may also be used to line the interiorof the culvert to prevent corrosion and abrasionor to reduce hydraulic resistance. For example, asphaltic concrete may be used to line corrugated metal culverts. The different shapes normally used in culvert construction include circular, rectangular (box), elliptical, pipe arch, metal box, and arch.✹The drainage problem is increased in these areas primarily for two reasons: the impervious nature of the area creates a very high runoff; and there is little room for natural water courses. It is often necessary to collect the entire storm water into a system of pipes and transmit it over considerable distances before it can be loosed again as surface runoff. This collection and transmission further increase the problem, since all of the water must be collected with virtually no pending, thus eliminating any natural storage; and through increased velocity the peak runoffs are reached more quickly.Also, the shorter times of peaks cause the system to be more sensitive to short-duration,high intensive rainfall.Storm sewers,like culverts and bridges,are designed for storms of various intensity-return-period relationships, depending upon the economy and amount of ponding that can be tolerated.✹Airport Drainage✹The problem of providing proper drainage facilities for airports is similar in many ways to that of highways and streets. However, because of the large and relatively flat surface involved, the varying soil conditions, the absence of natural water courses and possible side ditches, and the greater concentration of discharge at the terminus of the construction area, some phases of the problem are more complex. For the average airport the over-all area to be drained is relatively large and an extensive drainage system is required. The magnitude of such a system makes it even more imperative that sound engineering principles based on all of the best available data be used to ensure the most economical design.Overdesigning of facilities results in excessive money investment with no return, and underdesigning can result in conditions hazardous to the air traffic using the airport. In order to ensure surfaces that are smooth, firm, stable, and reasonably free from flooding, it is necessary to provide a system which will do several things.It must collect and remove the surface water from the airport surfaces; intercept and remove surface water flowing toward the airport from adjacent areas; collect and remove any excessive subsurface water beneath the surface of the airport facilities and in many cases lower the ground-water table; and provide protection against erosion of the sloping areas.路面公路的路面被分为两类：刚性的和柔性的。
