

OWNER:
Dow Chemical Company
CONTRACTOR:
Radion International, LLC
ENGINEER:
AWD Technologies, Inc.
Freeport, Texas
The owner proposed to place a final
soil cap over two industrial waste sludge ponds at their Freeport, Texas facility.
The surface area of the two ponds was approximately 8 and 11 acres, with a
sludge depth of nearly 18 feet. In-situ shear strength measurements indicated
that the shear strength of the soft sludge gradually increased from about
5 psf near the surface to about 35 psf near the bottom of the pond. A study
was conducted that suggested several options including: excavation, incineration
and disposal, sludge press and landfill, and solidification. The time and
costs associated with these alternatives, along with the extremely soft nature
of the sludge, resulted in Dow searching for alternatives. The owner’s
previous experience using geosynthetics to cap sludge led to development of
a plan to utilize biaxial geogrid and geotextile to construct an initial working
platform over the sludge. A lightweight fill consisting of tree bark was spread
over the geosynthetics using a prescribed construction technique and lightweight
equipment. A drainage system consisting of perforated pipes was installed
to collect and remove water expelled from the sludge during the consolidation
process. Once the initial lift of bark was completed, the final soil layer
was placed and graded to the desired contours using lightweight dozers. The
final soil cap was successfully completed and the project received an “Outstanding
Achievement” award from the Industrial Fabrics Association International
(IFAI) in 1996. The completed cap reduced the construction schedule by 80%,
while reducing costs by 25%, as compared to other alternatives considered.