Geosynthetics October/November 2022 - 9

DESIGNING REINFORCED
SOIL STRUCTURES
Q: Why is strain compatibility important
in designing reinforced soil walls?
A: When designing reinforced earth
structures, a vital aspect is the interaction
between the reinforcement and the
compacted soil, as this governs the overall
stability of the structure. The main function
of the reinforcement is to redistribute
the stresses within the soil structure
to enhance the internal stability of the
reinforced soil structure. The reinforcement
undergoes tensile strain as it transfers
loads from unstable to stable zones of
the soil. In designing reinforced soil walls,
strain compatibility of the geogrid to the
surrounding soil is critical. If the geogrid is not
matched (via a pullout test, i.e., ASTM D6706)
to the soil in which it is embedded, it will
not function optimally. One usually wants a
geogrid to pick up load rapidly when strained,
thus allowing minimal displacement.
LINER SYSTEM
LEAKAGE ESTIMATIONS
Q: What is the anticipated leakage rate
through a composite liner (i.e., geomembrane
on low-permeability soil) system?
A: The best way to answer this is with data.
Action leakage rates (ALRs) are design
targets for landfill containment facilities.
Accurate estimations of liner system leakage
are crucial for assessing the environmental
impact of landfill containment systems. At
right are graphs that illustrate leakage rates
at sites in the U.S. with double composite
liner systems and leak detection. They were
obtained from the following sources:
Figure 1: Gilson-Beck, A. (2022). " Technologies for
reducing the risk of landfill leakage, " Global Waste
Management Symposium (GWMS), Indian Wells, Calif.,
USA, Waste 360, 115-121.
Figure 2: Bonaparte, R., Daniel, D. E., and Koerner, R. M.
(2002). " Assessment and recommendations for improving
the performance of waste containment systems, " U.S.
Environmental Protection Agency, Washington, D.C.,
EPA/600/R-02/099 (NTIS PB2003-103048).
In all cases illustrated, the data is from doublelined
cells that have a very high level of
installation quality and construction quality
assurance (CQA). These sites utilize a systems
approach of good design by professional
engineers, quality materials, accredited
testing, best available installation by certified
installers, quality assurance by certified
FIGURE 1
inspectors, electrical leak integrity survey
prior to commissioning facility, and careful
operations and maintenance.
Two things should be noted:
* Most facilities must maintain a
leakage rate under 20 gallons per acre
per day (187 L/ha) or else they cannot
be permitted.
* The leakage rates are not zero,
which indicates we still have room
for improvement. G
>> For more, search Techline at
GeosyntheticsMagazine.com
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to gmatechline@textiles.org.
12.0
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8.0
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2.0
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Leakage Rate (gpad)
Average Primary Leakage Rates
Ref. 2002 Bonaparte,
Daniel & Koerner, USEPA
199 landfills
FIGURE 2
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