TM 5-826-6/AFR 93-5
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.
(2) Severity levels.
(a) Low severity level (L). Swell is barely visible and has a minor effect on the pavement's ride quality as
determined at the normal aircraft speed for the pavement section under consideration. (Low severity swells may not
always be observable, but their existence can be confirmed by driving a vehicle over the section at the normal aircraft
speed. An upward acceleration will occur if the swell is present) (fig. A-62).
Figure A-62. Low severity swell.
(b) Medium severity level (M). Swell can be observed without difficulty and has a significant effect on the
pavement's ride quality as determined at the normal aircraft speed for the pavement section under consideration (fig. A-
63).
Figure A-63. Medium severity swell.
(c) High severity level (H). Swell can be readily observed and severely affects the pavement's ride quality
at the normal aircraft speed for the pavement section under consideration (figs. A-64 and A-65).
Figure A-64. High severity swell.
A-37
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