Geosynthetics February/March 2022 - 21

travel. The project was the single largest
design-bid-build construction contract
ever awarded by the Virginia Department
of Transportation (VDOT) and was
awarded an Engineering Excellence Award
by the American Council of Engineering
Companies of Metropolitan Washington
(ACEC/MW EEA) and a transportation
engineering award from VDOT.
The design included a columnsupported
embankment with aggregate
piers and an LTP. VDOT specifically
requested high-strength geosynthetic
reinforcement with an ultimate tensile
strength of 38,000 pounds/foot (51.5
kN/m). A uniaxial geogrid manufactured
with high molecular weight and hightenacity
polyester multifilament yarns was
used in the project. Roughly 14,500 square
yards (12,100 m2) of geogrid were used
for basal reinforcement over aggregate
piers and under mechanically stabilized
earth (MSE) walls and slopes. The project
requested oversized geogrid panels, which
varied in length from 350 to 450 feet (106 to
137 m), were overlapped 2 feet (0.6 m) and
were tied together to prevent movement
during backfilling. Additionally, all overlaps
of geosynthetic panels were " shingled "
in the direction of the fill placement. This
ensured that the pushing of fill material
did not alter the careful overlap alignment.
Conclusions
Basal reinforcement over soft soils has
been used for several years as a practical
and economical alternative to traditional
ground improvement techniques.
One or multiple layers of geosynthetic
reinforcement can be installed directly
between the embankment fill and the soft
foundation soils to increase the design
safety factor and span between piles, as
well as to bridge sinkholes (Figure 8).
Design methods are available internationally
to properly identify the required tension
and subsequently the design strain. To
guarantee the required design life, installation
of the geosynthetic reinforcement
should be carefully carried out, preparing
a flat surface clear of sharp objects, ensuring
an accurate alignment of the rolls with
proper overlap between the end of one
roll and the beginning of the next one,
and providing continuous bond length or
edge anchoring.
References
ASCE. (1978). Soil improvement: History, capabilities, and
outlook, Ed. by J. K. Mitchell. American Society of Civil
Engineers, New York.
British Standards Institution. " Code of practice for
strengthened/reinforced soils and other fills. " BS80061:2010.
Collin,
J. G. (2004). " Column supported embankment
design considerations. " Proc., 52nd Annual Geotechnical
Conf., University of Minnesota, Minneapolis, Minn.
Collin, J. G., Watson, C. H., and Han, J. (2005). " Column
supported embankment solves time constraint for
new road construction. " Proc., ASCE Geo-Frontiers Conf.,
Austin, Texas.
Fowler, J., and Koerner, R. M. (1987). " Stabilization of
very soft soils using geosynthetics. " Proc., Geosynthetics
Conf. 1987, New Orleans, La., IFAI, St. Paul, Minn.,
289-300.
Mitchell, J. K. (1981). " Soil Improvement: State-of-theart. "
Proc., 10th International Conf. on Soil Mechanics and
Foundation Engineering, Vol. 4, Stockholm, Sweden,
509-565.
Rimoldi, P., and Scotto, M. (2012). " Design method for
geogrid reinforcement of road bases. " Proc., EuroGeo 5,
5th European Conf. on Geosynthetics, Valencia, Spain.
Rimoldi, P., and Simons, M. J. (2013). " Geosyntheticreinforced
granular soil mattress used as a foundation
support for mechanically stabilized earth walls. " Proc.,
GeoMontreal 2013 Conf., Montreal, Que., Canada.
Schaefer, V. R., Berg, R. R., Collin, J. G., Christopher, B.
R., DiMaggio, J. A., Filz, G. M., Bruce, D. A., and Ayala, D.
(2017). Ground modification methods reference manual,
Vols. I and II, Publication No. FHWA-NHI-16-028. Federal
Highway Administration (FHWA), U.S. Department
of Transportation, National Highway Institute,
Washington, D.C.
Sloan, J. A. (2011). " Column-supported embankments:
Full-scale tests and design recommendations. " Ph.D.
dissertation, Virginia Polytechnic Institute and State
University, Blacksburg, Va.
USACE. (1999). " Guidelines on ground improvement
for structures and facilities. " Technical Letter No. 11101-185.
Department of the Army, U.S. Army Corps of
Engineers, Washington, D.C. G
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One or multiple
layers of geosynthetic
reinforcement
can be installed
directly between the
embankment fill and
the soft foundation
soils to increase the
design safety factor
and span between
piles, as well as to
bridge sinkholes.
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Geosynthetics February/March 2022

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