CHANNELING. Channeling, also referred to as
grooving or rutting, is channelized depressions that
develop in the wheel tracks of flexible pavements (fig.
16-16). Channeling may result by consolidation or
lateral movement under traffic in one or more of the
underlying courses or by displacement in the bituminous
surface itself. It may develop under traffic in new
flexible pavements that had too little compaction during
construction or from plastic movement in a mix that
does not have enough stability to support traffic.
CORRUGATIONS AND SHOVING. Corru-
gation, or washboarding, are a form of plastic movement
typified by ripples across the flexible pavement surface
(fig. 16-17). Shoving is the plastic movement of the
pavement, resulting in localized bulging of the pavement
(fig. 16-18). Both corrugations and shoving normally
occur at points where traffic starts and stops or on hills
where vehicles brake on the downgrade.
Corrugations and shoving usually occur in flexible
pavement mixtures that lack stability. This may be the
result of too much binder, too much fine aggregate, or
round- or smooth-textured coarse aggregate. In the case
of emulsified and cutback asphalt mixes, it maybe due
to a lack of aeration.
DEPRESSIONS. Depressions are localized
areas of limited size that may or may not be
accompanied by cracking (fig. 16-19). Water collects in
depressions that then become not a source of pavement
deterioration but a hazard to motorists. Depressions are
caused by traffic heavier than that for which the
pavement was designed, by poor construction methods,
or by consolidation deep within the subgrade.
UPHEAVAL. Upheaval is the localized upward
displacement of the pavement due to swelling of the
subgrade or some portion of the pavement structure (fig.
16-20). It is commonly caused by ice expansion in the
granular courses beneath the pavement or in the