Flexible Pavement Design Procedures: Pavement Managers ...

Flexible Pavement Design Procedures Pavement Managers Workshop

August 6-8, 1985

Texas State Department of Highways and Public Transportation

Highway Design Division Pavement Design Section

FLEXIBLE PAVEMENT DESIGN PROCEDURES Pavement Managers Workshop August 6-8, 1985

INDEX

Chapter

Page

Flexible Pavement Design Procedures

1

Flexible Pavement Design System

5

Texas Triaxial Design Procedures

88

Swelling Clays In The FPS System

92

The FPS Traffic Equation

100

Appendix A Test Method Tex 117-E . .

A-107

"Triaxial Compression Test for

Disturbed Soils and Base Materials"

Appendix B "Modified Triaxial Design Procedure For Use With The Flexible Pavement Design System (FPS)"

A-129

FLEXIBLE PAVEMENT DESIGN PROCEDURES

FLEXIBLE PAVEMENT DESIGN PROCEDURES

Pavement Type Definitions

A discussion of pavement design makes it necessary to define the type of pavement being discussed. The two very basic types are "flexible" and "rigid" pavements. Definitions are very general and due to this fact they are varied. A very basic definition of pavement types is as follows:

Flexible - Asphalt Surface Rigid - Portland Cement Concrete Surface.

These definitions are arbitrary. The flexible pavement may become 11 slab-like" and assume many of the rigid pavement characteristics. The rigid pavement may lose this rigid posture and behave somewhat like the flexible pavement.

The flexible pavements may be subdivided into two very general areas:

1. Thin Surfaced Flexible Pavements 2. Semi-Rigid and Stabilized Pavements

The thin surfaced flexible pavements may be surfaced with either asphaltic concrete pavement or the surfacing may be single, double or triple surface treatment. The base course for the thin surfaced flexible pavements should be unbound or unstabilized. The key to the thin surfaced flexible pavement is its flexibility. The surfacing layer must be flexible enough to withstand the tensile strains without forming tensile cracks or fatigue cracking. The base material must be unstabilized so that tensile strains are not transmitted upward to the surfacing layer.

The semi-rigid or stabilized pavements are characterized by their thick and rigid surfacing layers. The subbase(s) in this type of pavement are also frequently stabilized. The key thought in this type of pavement is the ability to withstand tensile stresses without premature fatigue failures. This ability to tolerate the tensile stresses is a function of the rigidness and thickness of the surfacing layer(s). With sufficient rigidness and thickness the pavement layer assumes a semi-rigid slab like behavior. This rigid or slab like behavior aids in disipating the wheel load stresses into the base. subbase and subgrade layers .. The semi-rigid layer may actually be composed of several layers. The layers must be bonded together so that

- 1-

shear stresses are transmitted between layers. The layers may be a series of asphaltic concrete layers or there may be a mixture such as asphaltic concrete on cement treated base.

The surfacing layer thickness for the 11 thin surfaced flexible pavements" and the "semi -rigid and stabilized pavements .. and the reasoning for this concept will be discussed in another section of this report.

Definition of Flexible Pavement Design

Pavement design and especially flexible design divides itself into two tasks as follows:

1. Mixture or Materials Design 2. Structure or Thickness Design

Flexible pavement design divides itself into these two tasks but it is not intended to imply that these two tasks can be cleanly separated at the design stage and later joined into a happy reunion on the roadway. There must be interaction between the tasks; the thickness design assumptions must be achievable in the materials design stage and, likewise, the materials design stage must carry out the intent of the thickness design. Specifications are the link between mixtures and thickness design. Specifications are also the means by which both design phases are linked to construction and to maintenance of the pavement.

Figure 1, Pavement Relationships, point out that specifications are the link in the pavement design, construction and maintenance cycle. Also, the interaction or paths between functions is of interest. Obviously, all posssible pathways are not shown.

The objective of this report will be to treat only the structural or thickness design phase of flexible pavement design.

The Life Cycle of a Pavement

The design of pavements is but one of a series of steps in the life cycle of a pavement. During the life cycle of a pavement some of the major events could be as follows:

I. Planning 2. Preliminary Design 3. Programming (Funding)

-2 -

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download