Pavement materials are usually subjected to stress
levels that exceed their elastic limits to accommodate the
traffic loading with cost-effective design. Pavement
structures fail due to gradual accumulation of permanent
deformation, or degradation in materials during their
service life, and not due to rapid collapse (Sharp, 1985).
The mode of failure of unbound granular material (UGM)
layer is governed by the applied load and the shakedown
behavior of the material. Using the American Association
of State Highway and Transportation Officials (AASHTO)
road test data, and a case study conducted in Australia,
Sharp (1985) found that pavements subjected to lighter
traffic loading or with higher shakedown limits had longer
service lives.