Geosynthetic spins 'web' of success

Twelve years after installation, polyethylene cellular confinement system holds Wisconsin highway's base course in place as rest of road is prepared for reconstruction

Highway Construction Article December 28, 2000
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Wisconsin winters are notorious for the damage they can cause to roads.
An example of winter's influence was seen on Highway E, a winding, two-lane
asphalt road that serves commuters between Little Chute and Oneida. Once
called the worst stretch of road in Outagamie County, it was plagued by
cracking and heaving during the winter months. Similar problems occur elsewhere
in the region where sub-base sand silt pockets enclosed in the state's thick
clays become highly saturated and freeze.


The speed limit on a half-mile stretch of Highway E had to be reduced from
its normal 55 mph to 15 mph during the winter months. "Heaving could
start as early as November and be a problem through March," said Mike
Marsden, Outagamie County Highway Commissioner. "We could tell when
the frost was out of the ground in the spring because the road would flatten
out. We'd put up flashing barriers and advance warning signs. It was really
difficult to plow snow in the area."


Little did Marsden know that he'd find a solution to the heaving problem
in his own county. The corporate offices of Presto Products Co. and Presto
Geosynthetics are located in Appleton. The latter of the two companies helped
pioneer cellular confinement technology in cooperation with the Army Corps
of Engineers in the late '70s. The company's Presto Geoweb Cellular Confinement
System is designed to strengthen structural fill by increasing its shear
strength and stiffness.


The system originally was developed for building roads across insufficiently
supported grounds, such as beach sands. The system was used to build sand
roads for rubber-tire vehicles during the Persion Gulf War.


"Our first project with Outagamie County was at the county landfill
site," said Gary Bach, product manager. "We used the system to
construct an access road into one of the landfill cells. That application
was a success and led us to the Highway E project." To combat Highway
E's washboarding pavement, the county worked with the company in 1984 to
produce a cross-section design of the road. Presto staff were on site during
installation.


The system is an expandable honeycomb-like structure made of high-density
polyethylene. The system is designed to produce a stiff base with high flexural
strength. According to the company, under load, the system generates powerful
lateral confinement forces and high soil-to-cell wall friction. It is to
provide a bridging action and improve the long-term load deformation performance
of common granular fill materials.


On Highway E, an 8-in. deep system was installed in the problem area. The
asphalt pavement was removed and stored for recycling and final topping
after reconstruction. The silty clay sub-base was cut down 18 in. below
the water table level and covered with a geotextile. Next, a 6- to 8-in.
layer of 31¦2-in. to 41¦2-in. clean crushed stone was added. The
system was expanded, positioned and secured at the edges with granular fill.
It was then infilled with sand and topped with a 15-in. base course of crushed
stone. The completed area was then compacted with a vibratory roller and
was immediately ready for traffic.


"Because of our soil conditions, we always use a 15-in. base course
on all of our roads, Marsden said. "We probably could have gotten by
with less, but we decided not to. If we hadn't used the confinement system,
we probably would have reworked the subgrade and added 2 ft of base course.
Even though we had fill material available just 6 miles away, it was less
expensive to complete the renovation project with the Geoweb material than
without it."


Unpaved, the road performed well throughout the following winter, and was
surfaced with the recycled asphalt in the summer of 1985.


The system was installed in Highway E in 1984. Now, more than 10 years later,
the road still is level and holding up well under all weather conditions.
The highway is scheduled to be rebuilt in 1997. The county will widen the
highway, fill some valleys, improve sight distance and flatten curves.


"We're not going to touch the section of the road that has the confinement
system in it," Marsden said. "The road will be widened, but we
won't alter the alignment or the system. We're very pleased with the way
it has solved the problems for us on Highway E."

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