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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,Lesson 12Bituminous Surface Courses,The bituminous surface course has to provide resistance(抵抗) to the effects of repeated loading by tyres轮胎 and to the effects of the environment.,In addition, it must offer adequate skid resistance抗滑能力 in wet weather as well as comfortable vehicle ride. It must also be resistant to rutting 车辙and to cracking裂缝.,It is also desirable that surface course is impermeable不渗水的, except in the case of porous asphalt(多空隙沥青面层).,Hot rolled asphalt (HRA)热压沥青混凝土 is a gap graded 间断级配material with less coarse aggregate粗集料. In fact it is essentially a bitumen/fine aggregate细集料/filler填料 mortar胶浆 into which some coarse aggregate is placed.,The mechanical properties are 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 durable耐久的、耐用的 layer with good resistance to cracking and one which is relatively easy to compact压实. The coarse aggregate content is low (typically 30%) which results in the compacted mixture having a smooth surface. Accordingly因此, the skid resistance is inadequate and precoated预浇 chippings 石屑are rolled into the surface at the time of laying to correct this deficiency缺乏.,In Scotland, HRA wearing course remains the preferred wearing course on trunk roads干线道路 including motorway高速公路、汽车专用公路 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单一级配 material which is designed to provide large air voids空隙率 so that water can drain to the verges 路肩、边缘within the layer thickness. If the wearing course is to be effective, the basecourse基层 below must be waterproof 防水的and the PA must have the ability to retain its open textured 构造、纹理properties with time.,Thick binder films吸附沥青膜 are required to resist water damage水损害 and ageing老化 of the binder. In use, this material minimizes vehicle spray水雾, provides a quiet ride and lower rolling resistance to traffic than dense mixtures密级配混合料.,Bituminous Surface Courses,It is often specified指定 for environmental reasons but stone mastic asphalt (SMA)(沥青玛蹄脂碎石) and specially 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公路局 does not recommend the use of a PA at traffic levels above 6000 commercial vehicles载重车 per day.,Asphaltic concrete沥青混凝土 and dense bitumen macadam (DBM) 密级配沥青碎石are continuously graded mixtures连续级配混合料 similar in principle to the DBMs used in roadbases(基层) and basecourses but with smaller maximum particle sizes最大粒径.,Asphaltic concrete tends to have a slightly稍微 denser 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抗滑标准 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 pioneered开辟、开路 in Germany and Scandinavia and is now widely used in the UK. SMA has a coarse, aggregrate skeleton碎石骨架, like PA, but the voids are filled with a fine aggregate/filler填料/bitumen mortar.,In mixtures using penetration grade bitumen石油沥青 , fibres纤维 are added to hold吸收、吸附 the bitumen within the mixture (to prevent “binder drainage).,Bitumen,oil bitumen( earth oil),natural bitumen,Tar,Where a polymer modified bitumen 聚合物改性沥青is used, there is generally no need for fibres. SMA is a gap-graded material with good resistance to rutting and high durability耐久性.,modified bitumen,SBS,SBR,PEEVA,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矿质骨架.,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超的、极端的 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集中 in France.,These materials vary in their detailed constituents成分、要素、组成局部 but usually have an aggregate grading similar to SMA and often incorporate(联合、结合、参加) a polymer modified bitumen.,They may be used over a high stiffness roadbase and basecourse or used for resurfacing翻修路面 of existing pavements. For heavy duty pavements (i .e those designed to have a useful life of forty years), the maintenance philosophy哲学、哲理 is one of minimum lane occupancy占用, which only allows time for replacement 替换of the wearing course to these long life pavement structures. The new generation of thin surfacings allows this to be conveniently achieved.,The various generic种类的 mixture types described above can be compared with respect to their mechanical properties and durability characteristics by reference参考 to Fig.12.1. This shows, in principle, how low stone content HRA, asphaltic concrete, SMA and PA mixtures mobilize resistance(流动阻力) to loading by traffic.,Asphaltic concrete (Fig.12.1a) presents something of a compromise和解、折衷方案 when well designed, since the dense aggregate grading can offer good resistance to the shear stresses剪切应力 which cause rutting, while an adequate binder content will provide reasonable resistance to the tensile stresses拉应力,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 and away 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防止、制止 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.,Lesson 13,Drainage for Road and Airports,Provision of adequate drainage(排水 ) is important factor in the location定位 and geometric 几何学的、几何图形的 design of road and airports. Drainage facilities (排水设施 ) 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,(,最后、终于,),result in serious damage to the structure.,In addition, traffic may be slowed by accumulated water积水 on the pavement, and accidents may occur as a result of hydroplaning水滑现象 and loss of visibility from splash喷溅 and spray喷洒、喷雾.,The importance of adequate drainage is recognized in the amount of highway construction dollars,allocated,(,分配、分派,),to drainage facilities.,About 25 percent of highway construction dollars,are spent for erosion冲刷、侵蚀 control and,drainage structures, such as culverts涵洞,bridges, channels, and ditches明沟、渠.,Highway Drainage Structures公路排水结构物,One of the main concerns of the highway engineer is to provide an adequate size structure, such that the waterway opening过水孔径 is sufficiently large to discharge放、排出 the expected flow of water.,Inadequately sized structures can result in water impounding(集水、蓄水), which may lead to failure of the adjacent邻近的 sections of the highway due to embankments路堤 being submerged浸没、浸入水中 in water for long periods.,The two general categories of drainage structures are major and minor. Major structures大型结构物 are those with clear spans净跨径 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多孔涵洞 may also be included in this class. Minor structures include small bridges and culverts.,Emphasis is placed on selecting the span and vertical clearance净空 requirements for major structures. The bridge deck桥面 should be located above the high water mark高水位线 .The clearance above the high water mark depends on whether the waterway is navigable可通行的、可通航的.,混凝土连续箱梁,591-605,If the waterway is navigable, the clearance above the high water mark should allow the largest ship using the channel to pass underneath在下面 the bridge without colliding with(碰撞) the bridge deck.,The clearance height净空高度, type, and spacing of piers桥墩 also depend on the probability of ice jams冰块拥塞 and the extent程度 to which floating logs漂浮的圆木 and debris垃圾 appear on the waterway during high water.,武汉长江大桥,An examination of the banks堤岸 on either side of the waterway will indicate the location of the high water mark, since this is usually associated with signs of erosion冲刷、侵蚀 and debris deposits沉淀物、沉积物. Local residents, who have lived near and observed the waterway during flood stages洪水期间 over a number of years, can also give reliable可靠的 information on the location of the high water mark. Stream gauges水文站 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占优势的、主要的 type of drainage structures on highways. Although openings for these structures are not designed to be adequate for the worst flood conditions, they should be large enough to accommodate适应、容纳 the flow conditions that might occur during the normal life expectancy正常使用年限 of the structure.,Provision should also be made for preventing clogging障碍、阻塞 of the structure due to floating debris and large boulders圆石、巨砾 rolling from the banks of steep channels.,Drainage for Road and Airports,Culverts are made of different materials and in different shapes. Materials used to construct culverts include concrete reinforced and unreinforced, corrugated steel波纹钢筋, and corrugated波状的 aluminum铝. Other materials may also be used to line衬里 the interior内部、里面 of the culvert to prevent corrosion腐蚀、锈蚀 and abrasion磨损、磨耗、磨蚀 or to reduce hydraulic水力的、水压的 resistance.,For example, asphaltic concrete may be used to line corrugated metal culverts. The different shapes normally used in culvert construction include circular, rectangular 矩形的(box), elliptical椭圆形的, pipe arch, metal box, and arch.,Municipal城市的、市政的 Storm Drainage,In urban and suburban市郊的 areas, runoff waters 径流水are handled through a system of drainage structures referred to as storm sewers雨水管 and their appurtenances附属物.,The drainage problem is increased in these areas primarily for two reasons: the impervious不透水的 nature of the area creates a very high runoff; and there is little room for natural water courses水流.,It is often necessary to collect the entire storm water into a system of pipes and transmit传送、转达 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积水、积水库, thus eliminating any natural storage; and through increased velocity 速度the peak runoffs 最大流量are reached more quickly.,Also, the shorter times of peaks峰、顶峰 cause the system to be more sensitive灵敏的、敏感的 to short-duration持续时间短,high intensive强烈的、密集的 rainfall.Storm sewers,like culverts and bridges,are designed for storms of various intensity-return-period(强度重现期) relationships, depending upon the economy and amount of ponding积水 that can be tolerated.,Airport Drainage,The problem of providing proper drainage facilities排水设施 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水道 and possible side ditches边沟, and the greater concentration of discharge 流量、排出量at the terminus终点、界限 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数量、等级 of such a system makes it even more imperative强制的、不可防止的 that sound engineering principles 可靠的工程原理based on all of the best available data be used to ensure the most economical design.,Overdesigning过于平安的设计 of facilities results in excessive money investment with no return, and underdesigning欠平安的设计 can result in conditions hazardous to the air traffic using the airport.,Drainage for Road and Airports,In order to ensure surfaces that are smooth, firm巩固, stable稳定, 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(阻断、拦截) and remove surface water flowing toward the airport from adjacent areas; collect and remove any excessive subsurface water地下水 beneath the surface of the airport facilities and in many cases lower the ground-water table地下水位; and provide protection against erosion of the sloping areas.,Lesson14Freeways,Freeways, especially those built to Interstate洲际的、洲间的 standards are the safest of the various classes of highways.,While control of access(出入), which limits vehicle conflicts车辆冲突, is a primary factor in relatively low accident, injury, and fatality rates死亡率, other design features, such as wide medians中央分隔带 and shoulders, roadsides clear of obstructions路边无障碍物, and the extensive use of protective barriers护栏, are key factors as well.,Freeways,The higher design speeds used for freeways result in long sight distances due to long radius horizontal curves and long vertical curves, and other desirable design features that create a safe driving environment. Although most of the nations freeways enjoy this relatively high level of design and safety, there are many opportunities for further enhancements加强、提高. Safety improvements on freeways can also result in substantial savings in life and property生命和财产 because freeways carry 25 percent of the nations total traffic.,Freeways,Selecting the design speed for a freeway is an important safety element because most geometric criteria几何线形标准 are related to or depend on it. In general, 110 kilometers per hour (km/h) should be the design speed for the mainline主线 of a freeway, but it may need to be lower in areas of severe terrain or heavy development.,Freeways,For reconstruction, rehabilitation修复、重建, and resurfacing (3R)罩面 projects, the design speed should not be less than the original design speed or the current legal speed limit of that highway section.,Freeways,Design speeds for interchange ramps depend on the type of ramp selected, for example, loop, diamond, or direct, and the low-volume交通量低的, running speed 行车速度of the intersecting 相交highway. Usually, the design speed is established by the most restrictive 限制的、特定的element of the ramp, typically, the sharpest curve小半径曲线. Whatever design speed is selected, adequate transitions过渡、缓和 from the freeway proper and at the ramp terminal or merge point 合流点should be developed.,Freeways,Safe and efficient traffic operations depend on adequate lane and shoulder widths as outlined略述、画轮廓 in A Policy on Geometric Design of Highways and Streets. The need to accommodate 适应、容纳more traffic within existing or limited additional right-of-way道路用地权 on high-volume urban freeway has led some agencies to increase capacity by exchange变换 full-lane or shoulder widths for additional travel lanes with reduced widths.,Freeways,Any proposed use of less-than-full-standard低于标准的 cross-sections must be analyzed carefully on a site-by-site现场的 basis. Experience indicates that 3.3-m lane can operate safely if there are no other less-than-standard features; however, combined with shoulder-width reductions, substandard sight distance, and other features, 3.3m lanes may not provide the same safe operation. Converting变换、改造 shoulders to travel lanes for additional capacity through a short bottleneck section瓶颈路段 has been shown to significantly reduce congestion-related accidents on some projects. Removing shoulders for several kilometers, however, has not had the same result.,Freeways,Pavement marking路面标线, such as lane lines车道线， edge lines 车道边线， channelizing lines渠化线 at interchanges and ramps, and word and symbol markings, provide important information to the driver. Pavement markings define separate lanes of traffic traveling in the same direction, inform drivers of lane restrictions, and convey certain regulation and warnings that would not otherwise be clearly understood.,Freeways,Pavement markings are particularly important at night and during inclement weather恶劣天气 and, therefore, must be retroreflective(定向反光的). While well-maintained painted pavement markings are acceptable, thicker, long-life markings, such as thermoplastic (热塑性材料的)or preformed tapes预制的, may perform better in wet weather and heavy traffic.,Freeways,Some studies have been made regarding the benefits of wider edge line markings (150 to 200 mm versus the standard 100 mm width). The wider markings may particularly benefit older drivers.,Freeways,Raised or recessed retroreflective pavement markers significantly enhance all types of standard markings, especially during heavy rain at night when standard markings are not readily visible. Hence, they are recommended for use on freeway whenever cost-justified. Raised markers are placed on the pavement surface, and recessed markers are placed in shallow ground-out troughs.,Freeways,It has been estimated that 8 billion hours of excess travel occur each year because of navigational errors that are partly due to inadequate signing, amounting to an average of 34 hours per year for every person in the United States. Appropriate highway information systems are needed to ensure that motorists have adequate time to acquire and process the information for control, guidance, and navigation. On the other hand, the lack of signs or misleading signs can contribute to driver confusion, loss of attention, and erratic maneuvers.,Freeways,Signing for freeways should be planned concurrently with the geometric design. Trying to sign after interchange geometrics and spacings have been finalized has often resulted in poor signing design and operational problem.,Freeways,However, poor freeway design cannot be overcome by signing. Freeway signing should be consistent, easy to read, and unambiguous for the benefit and direction of drivers who are unfamiliar with the highway. In rural areas, the tendency to group all signing near the interchange should be avoided. Signs should be adequately spread on the approach and departure from each interchange.,Freeways,They should be places at natural target locations to command the drivers attention, especially where there are long distance between interchanges and the alignment is relatively constant.,Freeways,In areas with relatively close interchange spacing, the principle of sign spreading should be followed. Sign spreading helps disperse information so that motorists are not overloaded with a group of signs near the gore where path direction decisions
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