Swelling

A swell is characterized by an upward bulge in the pavement's surface. A swell may occur sharply over a small area or as a longer, gradual wave. Either type of swell can be accompanied by surface cracking. A swell is usually caused by frost action in the subgrade or by swelling soil, but a small swell can also occur on the surface of an asphalt overlay (over PCC) as a result of a blowup in the PCC slab.

Severity	Distress Example	Description
Low		Swell is barely visible and has a minor effect on the pavement's ride quality. Low-severity swells may not always be discernible, but their existence can be confirmed by driving a vehicle over the section. An upward acceleration will occur if the swell is present.
Medium		Swell can be observed without difficulty and has a significant effect on the pavement's ride quality.
High		Swell can be readily observed and severely affects the pavement's ride quality.