8 路面设计.ppt

PAVEMENT DESIGN 路面设计 The function of the pavement structure is to distribute imposed wheel loads over a large area of the natural soil（天然土层）. If vehicles were to travel on the natural soil itself, shear failures（剪切破坏） would occur in the wheel path（轮迹） in most soils, and ruts（车辙） would form. The shear strength（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（面层） of a highway or airport pavement structure must provide a level, safe traveling surface. Pavements are classified as “rigid（刚性）” or “flexible（柔性）”, depending on how they distribute surface loads. The flexible pavement consists of a relatively thin wearing surface built over a base course（基层）, and subbase course（底基层）, and they rest upon the compacted subgrade. In contrast, rigid pavements （刚性路面）are made up of Portland cement concrete and the subgrade. The thickness of the flexible pavement （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 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, 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 concrete. For this reason, minor variations(变化) in subgrade strength have little influence upon the structural capacity of the pavement. Base courses are us