Geosynthetics April/May 2020 - 30

Geosynthetic strip MSE wall at Point Defiance Marina

properties of both the select and random
backfills have a significant impact on the
design of the geosynthetic strip MSE wall.
Specifications for select backfill should
meet the following guidelines:
* Well drained
* Not prone to postconstruction
movement/settlement
* Durable and does not break down
or change its properties during
construction
* Not aggressive to geosynthetics

FIGURE 7 Example of MSE backfill placed
on geosynthetic strip

If on-site backfill does not meet these
guidelines, imported select backfill may
be required or modifications to the design
and construction procedures may be considered after careful assessment by the
engineer and contractor. On this project,
imported select backfill conforms with
the requirements shown in Table 1.
Using the low fines aggregate backfill allowed MSE wall construction in
the rain. Installation of the MSE wall
began during late fall of 2017. Battling
constant rainfall during construction
became a normal occurrence on the
project. Furthermore, tidal influence
was expected. At the time of setting the
bottom row of panels, the water level
reached the top of the leveling pad.
Backfill placement followed conventional MSE wall construction allowing
rubber-tired vehicles to operate directly
on the exposed geosynthetic strips. An

example of backfill placed on top of the
geosynthetic strip is shown in Figure 7.

Further project applications
The first geosynthetic strip reinforced MSE
wall with integrated connections of this
type was put in service in 2005 in Morzine,
France. Since then more than 400 geosynthetic strip MSE walls have been constructed in 33 countries. The geosynthetic
strip MSE wall has applications in all environments, especially those aggressive to
galvanized-steel reinforcement. In the U.S.,
a tall 46-foot (14-m) high geosynthetic
strip MSE wall was constructed for a dam
raising at the Los Vaqueros Reservoir
in northern California (Hardianto et al.
2013). A geosynthetic strip MSE wall was
specified by the owner to avoid the potential for metal loss by-products to leach
from backfill into the reservoir.
The Florida Department of
Transportation (FDOT) has implemented
restrictions related to MSE wall location
and nearby marine environments. With
this standard in place, the geosynthetic
strip MSE wall satisfies the restriction and
allows MSE walls to continue to be constructed where steel reinforcements would
not be feasible. FDOT has embraced this
technology and continues to take advantage of the architectural possibilities available with the precast facing panels of the
geosynthetic strip MSE wall system.

Property

Test Method

Requirement

Gradation: Well-Graded Backfill

AASHTO T-27

Percent Passing: 102 mm (100%),
76 mm (75-100%), No. 40 (0-60%)

Plasticity Index

AASHTO T-90

Not to exceed 6

Soundness (Magnesium sulfate after 4 cycles)

AASHTO T-104

Less than 30%

pH Range

AASHTO T-289-911

4.5-9

Organic Content

AASHTO T-267

Not to exceed 1% of the total sample

* The typical AASHTO standard for passing the No. 200 Sieve is 15% maximum. This project limited fines to only 5%,
following Washington State Department of Transportation gravel borrow specification.
TABLE 1 MSE wall backfill properties
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Geosynthetics April/May 2020

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