路面设计外文翻译---柔性路面设计

英文翻译

Flexible pavement design

Generally 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 alphalt

concrete 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.