Oklahoma local government news, winter 1993

              Z 2135.6 L811g
Winter 1993
OKLAHOMA LOCAL GOVERNMENT NEWS
PUBLISHED QUARTERLY BY THE CENTER FOR LOCAL GOVERNMENT TECHNOLOGY, OKLAHOMA STATE UNIVERSITY, SPONSORED JOINTLY BY THE
FEDERAL HIGHWAY ADMINISTRATION, THE OKLAHOMA DEPARTMENT OF TRANSPORTATION AND THE OKLAHOMA COMMISSION ON COUNTY
GOVERNMENT PERSONNEL, EDUCATION AND TRAINING.
308 CITD
Stillwater, OK
74074
405-744-6049
Winter 1993
edited by Douglas Wright
What Causes Recurring Wheelpath Ruts?
Question...
Our road department built a one inch hot-mix overlay on a road that
showed moderately deep narrow ruts in the wheelpaths. After a few
months of summer traffic, the ruts came right back again. What caused
this to happen?
Answer...
There are a variety of factors that could contribute to wheelpath
rutting. The ruts came so quickly that possibly it was because you did
not put down a leveling course.
A leveling course is a thin layer of sand-asphalt mix placed on top of the
old road surface, just deep enough to fill the ruts. It should be
OVERLAY
FIG.   2
compacted immediately using a
pneumatic rubber-tired roller.  (A
steel drum roller will bridge across
the ruts and not properly compact
the mix.)
Because the leveling course is so
thin, it must be placed on a very hot
day in the middle of the summer.
Also, to compact it well,  the roller
must be used on it immediately. It
is usually a good idea to let traffic
run on it for a few days to help
compact it before placing the
overlay on top.
The leveling course helps to prevent
the return of the wheelpath ruts. An
overlay placed above the leveling
course will be a uniform thickness
across the lane as in Figure 1.
When compacted (typically by a
steel drum roller), the density is
achieved, traffic will not have much
effect on it.
If the leveling course is omitted, the
overlay, when placed, will be thicker
in the wheelpaths by the amount of
the rut depth, as shown in Figure 2.
When the overlay is compacted, the
material between the wheelpaths gets
more compaction effort than the
material in the wheelpaths because it
is thinner. Traffic gradually
compacts the material in the
wheelpaths, and the ruts reappear.