英文翻译Flexible pavement designGenerally speaking,pavements(and bases) may be divided into two broad classifications or tipes:rigid and flexible. As commonly used in the United States,the term “rigid pavement”is applied to wearing surfaces constructed of Portland-cement concrete. A pavement constructed of concrete is assumed to possess considerable flexural strength that will permit it to act as a beam and allow it to bridge over minor irregularities which may occor in the base or subgrade on which it rests;hence the term “rigid”.Similarity,a concrete base that supports a brick or block layer might be described as “rigid”.All other types of pavement have traditionally been classed as “flexible”.A commonly used definition is that “a flexible pavement is a structure that maintains contact with and distributes loads to the subgrade and depends on aggregate interlock,particlefriction,and cohesion for stability”.Thus,the classical flexible pavement include primarily those pavement that are composed of a series of granular layers topped by a relatively thin high-quality bituminous wearing surface .Typically,the highest-quatily materials are at or near the surface.It should be pointed out that certain pavementsthat have an asphalt surface may behave more like the classical “rigid”pavement,for example, pavement that have very thick asphalt surface or that have base courses composed of aggregate treated with asphalt,cement, or lime-fly ash. However,for convenience of presentation,these pavements will be considered to be in the flexible class.The structure of flexible pavement is composed of a “wearing surface”, base, subbase(not always used), and subgrade . The wearing surface and the base often comprise two or more layers that are somewhat different in composition and that are put down in separate construction operations.On many heavy-duty pavements,asubbase of select material is often placed between the base and subgrade.the wearing surface may range in thickness from less than 1 in. in the case of a bituminous surface used for low-cost, light-traffic loads to 6 in. or more of alphaltconcrete used for heavily traveled routes. The wearing surface must be capable of withstanding the wear and abrasive effects of moving vehicles and must possess sufficient stability to prevent it from shoving and rutting under traffic loads. In addition,it serves a useful purpose in preventing the entrance of excessive quantities of surface water into the base subgrade from directly above.The base is a layer (or layers) of very high stability and density. Its principle purpose is to distribute or “spread” the stresses created by wheel loads acting on the wearing surface so that the stresses transmitted to the subgrade will not be sufficiently great to result in excessive deformation or displacement of that foundation layer. The base must also be of such character that it is not damaged by capillary water and/or frost action. Locally available materials are extensively used for base construction, and materials preferred for this type of construction vary wwidely in different sections of the country. For example, the base may be composed of gravel or crushed rock or it may bae a granular material treated with asphalt,cement,or lime-fly ash stabilizing agents.Asubbase of granular material or stabilized material may be used in areas where frost action is severe, in locations where the subgrade soil is extremely weak. It may also be used , in the interests of economy ,in locations where suitable subbase material are cheap than base materials of higher quality.The subgrade is the foundation layer, the structure that must eventually support all the loads which come onto the pavement. In some cases this layer will simply be the natural earth surface. In other or more usual instances it will be compacted soil existing in a cut section or the upper layer of an embankment section. In the fundamental concept of the action of flexible pavement,the combined thickness of subbase (if used), base, and wearing surface must be great enough to reduce the stresses occuring in the subgrade to values that are not sufficiently great to cause excessive distortion or displacement of the subgrade soil layer.The principle factors entering into the problem of the thickness design of flexible pavement are:(1)Traffic loading.(2)Climate or environment.(3)Material characteristics.A number of other elements must also be considered in order to arrive at a final thickness design. This include cost, construction, maintenance,an design period. Thus, the students should realize that the design process is complex, and it is highly unlikely that any extremely simple method of approach will prove entirely successful under all conditions.Protection of the subgrade from the loading imposed by traffic is one of the primariy functions of a pavement structure. The designer must privide a pavement that can withstand a large number of repeated applications of variable-magnitude loading.The magnitude of maximum loading is commonly controlled by legal load limits. Traffic surveys and loadometer studies are often used to establish the relative magnitude and occurrence of the various loading to which a pavement is subjected. Prediction or estimation of the total traffic that will use a pavement during its design ife is a very difficult but obviously important task.The climate or environment in which a flexible pavement is to be established has an important influence on the behavior and performance of the various in the pavement and subgrade. Probablly the two climate factors of major significance are temperature and moisture.The magnitude of temperature and its fluctuations affect the properties of certain materials. For example, high temperatures cause asphaltic concrete to lose stability whereas at low temperatures asphaltic concrete becomes very hard and stiff. Low temperature and temperature fluctuations are also associated with frost heave and freeze-thaw damage.Granular materials, if not properly graded, can experience frost heave. Likewise, the subgrade can exhibit extensive loss in strength if it becomes frozen. Certain stabilized materials (lime, cement, and lime-fly ash treated) can suffer substantial damage if a large number of freeze-thaw cycles occur in the material.Moisture also has an important influence on the behavior and performance ofmany materials. Moisture is an important ingredient in frost-related damage. Subgrade soils and other paving materials weaken appreciably when saturated, and certain clayey soil exhibit substantial moisture-included volume change.Subgrade moisture conditions change is affecting road structural strength, stiffness and stability of the important factors. Subgrade moisture influence has the following main factors: atmospheric precipitation and evaporation, infiltration of surface water, groundwater impact, temperature changes caused by humidity. Cyclical atmospheric temperature changes throughout the year, day and night temperatures for each day a certain extent cyclical changes. Surface directly exposed to the air, and experiencing the impact of these changes, in particular surface material most affected. Road surface temperature change with the weather temperature is roughly synchronized. Surface layer temperature at different depths within the same generation as the cyclical changes in atmospheric temperature, but the magnitude of change increases with the depth gradually decreased.One of frost damage is frozen, it not only affects the normal running of vehicles, and sometimes the destruction of the pavement structure. Produce frost heave for two reasons: First, as water is frozen, the volume will increase by 9%; second is due to the weak foundation soil to freeze the area with water movement results. Subgrade frost heaving caused by three factors: the sensitivity of frozen soil subgrade; temperature decreased slowly; groundwater supply of water to keep the frozen zone.The advent of spring, began to melt the frozen roadbed, will lose their bearing capacity of soil, leading to road damage, a phenomenon known as the spring melt boil, boil and mainly due to the melting process is top down, when the embankment top soil begins to melt, the water can not be excluded, so the soil has been saturated melting. If by this time a large number of heavy vehicles, road structure would be seriously damaged.Of the road is a sticky, elastic-plastic materials and the combination of mineral aggregate particles consisting of roads, including the addition of cement concrete as a surface layer and the surface structure of a variety of other grass-roots level. Flexible pavement design including pavement layer combination of design, structuralcalculation and the road pavement material mix design. This chapter elaborates the following aspects: elastic layered system theory, the pavement layer combination of design principles, road design standards and parameters, calculation of pavement thickness and the bending stress check.In reality, the road base material and the soil is not in any case have elastic properties. Non-linear elastic - viscous - plastic theory, under certain conditions more accurately describe the stress state of the road, but taking into account the role of the transient driving wheels in the pavement structure, the stress was small, so you can road as each layer is an ideal elastic body, multi-layer linear elastic theory to application to design calculations. Multi-layer linear elastic theory must be used the following basic assumptions:yers of material are continuous, homogeneous, isotropic and to obey Hooke's law, and the displacement and deformation is small;2. The next level (soil basis) in the horizontal direction and vertical direction down to infinity, The elastic layer is above all have a certain thickness, but the horizontal direction is infinite;3. layers of infinite distance in the horizontal direction and the next layer down to infinite depths, the stress, strain and displacement is zero;4. layers the contact conditions between fully continuous;5. do not count weight.Flexible Pavement Structure Design's mission is to design principles in general under the guidance of the road, according to the road level, requirements and design life of the cumulative equivalent standard axle load axle, considering the supply of road materials, the degree of influence of natural factors and the specific construction conditions, determine a reasonable level of the pavement structure and select the appropriate economic composition materials, combined into both withstand traffic loads and the role of natural factors, but also give full play to the maximum performance of structural materials, subgrade layer pavement system. Combination of flexible pavement structural design should follow the following basic principles:1, route, embankment, road do take into consideration the overall design;2, according to the structure, function and transport layer characteristics of selected structural levels;3, the strength to adapt to traffic load and stiffness combination;4, pay attention to its own characteristics each layer, make layer combination;5, the appropriate number of layers and thickness;6, to consider the impact of water temperature conditions to ensure stability.柔性路面设计一般来讲，路面（和路基）可以分为两种类型：刚性路面和柔性路面。