(1) The subgrade must be able to sustain traffic loading without excessively
deforming. This is achieved by limiting the vertical stress at formation level.
(2) Bituminous or cement bound materials used in the flexible pavement must
not be subject to fatigue cracking. This is achieved by limiting the
horizontal tensile stresses at the bottom of the bituminous/cement bound
roadbase.
(3) The load spreading capability of granular subbases should be enough to
provide an acceptable construction platform.
(4) When a pavement is composed of a considerable depth of bituminous
material, its creep must be restricted in order to stop the rutting which
arises from internal deformation.