b. During the functional or service phase, the pavement carries the

 anticipated traffic without undue deformation and the deflection

 remains fairly constant or shows a slight decrease.

 c. The failure phase occurs as a result of both traffic and envi-

 ronmental factors. In this phase the deflection increases

 rapidly and there is a rapid deterioration resulting in failure

 of the pavement structure.

5. The deflection history of a pavement system varies throughout the

 year due to the effects of frost, temperature, and moisture. A

 typical annual deflection history of a pavement subjected to frost

 action, as shown in Figure 2.2, can be divided into the following

 four periods (103):

 a. The period of deep frost when the pavement is the strongest.

 b. The period during which the frost is beginning to disappear from

 the pavement structure. During this period, the deflection

 rises rapidly.

 c. The period during which the water from the melting frost leaves

 the pavement structure and the deflection begins to drop.

 d. The period during which the deflection levels off with a general

 downward trend as the pavement structure continues to slowly dry

 out.

6. For a given flexible pavement structure it is generally known that

 the magnitude of the deflection increases with an increase in the

 temperature of the bituminous surfacing material. This is due to a

 decrease in the stiffness of the bituminous surfacing. The effect

 of temperature varies with the stiffness of the underlying layers.

 As the stiffness of the underlying layers increases, the effect of