Geosynthetics February/March 2024 - 18

Improving the performance of geosynthetic reinforced SRW by design
FIGURE 5 Intermediate layers: Computed Tmax and To in each layer [max(Tmax)=7.5 kN/m
(approx. 514 lb/ft); max(To)=6.8 kN/m (approx. 466 lb/ft)].
at 0.2 m (approximately 2 feet), each 1.2
m (approximately 4 feet) long, were used:
the amount of added reinforcement in
this case is small while the benefits could
be significant. Looking at the distribution
of T(x), the maximum Tmax is 0.31
kN/m (approximately 21 lb/ft), a very
low value. That is, because formally this
slope is stable (albeit marginally), the
reinforcement is likely to be dormant but
when needed, this low strength may play
a significant role. Using weak reinforcements
in stabilizing a slope above the wall,
constructed by the site contractor, may
improve the performance of the wall by
serving as a safeguard against common
imperfect construction and field conditions
(e.g., transient flow of water) while
facilitating compaction of a " secondary "
element of the wall system.
The amount of geosynthetics needed
FIGURE 6 Reinforced broken backslope
466 lb/ft), about 80% of the primary reinforcement
only. Many of the upper layers
carry much smaller connection loads;
these layers are under the immediate
surcharge of the broken backslope. The
added intermediate layers reduce both
connection and reinforcement loads,
allowing for use of weaker reinforcements
or, more importantly, adding stability at
the front end of the SRW analyzed.
So far, we have treated the broken
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backslope as a slope above the reinforced
wall. However, its inclination 1:2 (26.6
degrees) is quite steep considering a
friction angle of ϕ=30 degrees for the
backfill soil. It can be shown that, under
unreinforced conditions, such a condition
renders a factor of safety of about
1.15. This is a marginal value in design
of slopes even though failure might be of
shallow or sloughing type. Requiring a
global factor of safety of 1.5, common in
design of slopes, and using the method by
Leshchinsky et al. (2016), one gets the distribution
shown in Figure 6. Note that to
facilitate compaction, short layers spaced
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Geosynthetics | February March 2024
for the baseline design is 420 m2 per
meter length of wall (approximately 1380
ft2 per foot length of wall). The added
area of secondary reinforcement is 22.8
m2 per meter length of wall (approximately
75 ft2 per foot length of wall). The
added reinforcement in the backslope
zone is 4.8 m2 per meter length of wall
(approximately 16 ft2 per foot length of
wall). If one implements the facing and
backslope improvements, a total of 27.6
m2 per meter length (approximately 90
ft2 per foot length) of extra geosynthetic
is needed; i.e., about 6.5% more reinforcement
compared with the baseline design.
Installing these additional geosynthetic
materials also means a minor increase in
construction costs. However, cost of failure
is difficult to estimate before it actually
happens; i.e., it is difficult to assess
potential savings resulting from improved
wall performance. Generally, based on
the authors' experience, failure cost is
high, much more than the cost of extra
reinforcement to prevent such failure. It
should be noted that the rational use of
intermediate or secondary layers allows
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Geosynthetics February/March 2024

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