16 Lecture 7 130414 PAVEMENT DESIGN Elements of a Flexible Pavement The

16 lecture 7 130414 pavement design elements of a

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Lecture 7 13/04/14 PAVEMENT DESIGN Elements of a Flexible Pavement The structural components of a flexible pavement are the Subgrade (basement soil, roadbed), the Subbase , the Base , and the Wearing surface. The intersection of the subgrade and the superimposed pavement is known as the formation . The performance of the pavement depends on the satisfactory performance of each component. This basic structure remains essentially the same, whether the pavement is for an expensive motorway or a simple rural road. SUBGRADE This is usually the natural material located along the horizontal alignment of the road and serves as the foundation of the pavement structure. The subgrade may also consist of a layer of native soil materials exposed by excavation and to selected borrow materials that may be artificially deposited to form a compacted foundation. It may also be necessary to treat the subgrade material to achieve certain strength properties required for the type of pavement being constructed. 17
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Lecture 7 13/04/14 PAVEMENT DESIGN SUBBASE The subbase is located immediately above the subgrade and consists of a material of superior quality to that which is generally used for subgrade construction. It may or may not be present in the pavement as a separate layer. The function of the subbase include the following: As a structural member of the pavement the subbase helps to distribute the applied loads to the subgrade. The subbase material must always be significantly stronger than the subgrade material and capable of resisting within itself the stresses transmitted to it via the roadbase. A coarse grained material may be used in the subbase to act as a drainage layer to drain off any moisture that falls during or after construction. The quality of the material so used must be such that the subbase can drain freely always 18
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Lecture 7 13/04/14 PAVEMENT DESIGN SUBBASE (cont’d) On fine-grained subgrade soils a granular subbase may be provided to: Carry construction traffic and act as a working platform on which subsequent layers can be constructed Act as a cut-off blanket and prevent moisture from migrating upward from the subgrade To act as a cut-off blanket to prevent the infiltration of subgrade material into the pavement 19
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Lecture 7 13/04/14 PAVEMENT DESIGN ROADBASE Not to be confused with the basecourse, which is an integral part (a sub- layer) of the surfacing (surface course). From a structural point of view, the road base is the most important layer of a flexible pavement. It lies directly above the subbase and is normally the thickest layer of the pavement. It is expected to bear the burden of distributing the applied surface loads so that the bearing capacity of the subgrade is not exceeded.
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  • Summer '14
  • Freeway, Motorway, roundabout, Grade separation, At-grade intersection, Turbo Roundabouts

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