8 路面设计.ppt
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1、 PAVEMENT DESIGN 路面设计路面设计 The function of the pavement structure is to distribute imposed wheel loads over a large area of the natural soil(天然土(天然土层).If vehicles were to travel on the natural soil itself,shear failures(剪切破坏)(剪切破坏)would occur in the wheel path(轮迹)迹)in most soils,and ruts(车辙)would for
2、m.The shear strength(剪切强度)(剪切强度)of the soil is usually not high enough to support the load.In addition to its load distribution function,the surface course(面(面层)of a highway or airport pavement structure must provide a level,safe traveling surface.Pavements are classified as“rigid(刚性)性)”or“flexible(
3、柔性)(柔性)”,depending on how they distribute surface loads.The flexible pavement consists of a relatively thin wearing surface built over a base course(基(基层),and subbase course(底基(底基层),and they rest upon the compacted subgrade.In contrast,rigid pavements(刚性路面)性路面)are made up of Portland cement concrete
4、 and the subgrade.The thickness of the flexible pavement(柔性路面)(柔性路面)is meant to include all components of the pavement above the compacted subgrade.Thus,the subbase,base,and wearing surface are the structural components of the pavement.In the case of the rigid pavement,the concrete,exclusive of the
5、base,is referred to as the pavement.In some cases,Portland cement concrete is used as a base course for a flexible-type wearing surface.The essential difference between the two types of pavements,flexible and rigid,is the manner in which they distribute the load over the subgrade.the rigid pavement,
6、because of its rigidity and high modulus of elasticity,tends to distribute the load over a relatively wide area of soil;thus,a major portion of the structural capacity is supplied by the slab itself.The major factor considered in the design of rigid pavements is the structural strength of the concre
7、te.For this reason,minor variations(变化化)in subgrade strength have little influence upon the structural capacity of the pavement.Base courses are used under rigid pavements for various reasons,including(1)control pumping(唧泥)泥),(2)control of frost action(冻胀)(3)drainage(排水)(排水),(4)control of shrink and
8、 swell(胀缩)of subgrade and(5)expedition of construction(施施工速度工速度).The base course will lend some structural capacity to the pavement;however,its contribution to the load-carrying capacity(承(承载力)力)is relatively minor.The load-carrying capacity(承(承载力)力)of flexible pavements is brought about by the load
9、-distributing characteristics of the layered system(层状状体系)体系).Flexible pavements consists of a series of layers,with the highest quality materials at or near the surface.Hence,the strength of a flexible pavement is a result of building up thick layers and thereby distributing the load over the subgr
10、ade,rather than by the bending action of a slab.The thickness design of the pavement is influenced by the strength of the subgrade.Subbase courses for flexible pavements are generally made up of cheap,locally available materials,whereas the base courses are higher quality processed materials(处治的材治的材
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