Geosynthetics August/September 2019 - 36

An innovative cover system to close an ash/sludge impoundment

The geomembrane
could be deployed
rapidly, containing
the odor and
preventing it from
going off-site. With
the odor contained,
relations with the
local community
improved dramatically.

provides an optimum particle
size distribution so as to promote
maximum interlocking of the
particles, which when combined
with the PE tufted fibers, yields
less than 2% total cumulative particle movement.
b. Cementitious infill mix: Based
upon a thin-set Portland cement
technology, the cementitious
infill is used in areas of high
hydraulic velocity and shear
stress typically associated with
concentrated hydraulic flow, such
as those found in downchutes or
high-flow channels.
c. Emulsion binder: A polymeric
binding agent is used in conjunction with the ASTM C33 sand to
provide a hardened but highly
permeable layer in which the
sand ingredients are chemically
locked into place. This binder
will last a minimum of five years
from initial application and can
be recharged through the reapplication of emulsion at a concentration rate of 10%-20% of
the original rate to obtain at least
five additional years of protection. The emulsion binder provides infill protection for transition zones between hydraulic and
nonhydraulic areas, or for clients
who wish to eliminate any possibility of sand infill movement,
no matter how slight.

Project solution selection
The project team assessed the TG-FCS
against the identified priorities of odor
elimination, construction schedule and
lifetime cycle costs.
Odor elimination
The TG-FCS provided specific benefits
with respect to the odor elimination
36

Geosynthetics | August September 2019

objective. The geomembrane could be
deployed rapidly, containing the odor and
preventing it from going off-site. With
the odor contained, relations with the
local community improved dramatically.
This benefit to the client and project team
cannot be overstated.
The TG-FCS eliminates the typical soil burden associated with traditional cover systems, as well as the corresponding heavy equipment needed
to move, place and grade this soil. This
system can be installed using only light
ground-pressure vehicles. This allowed
for far more rapid deployment of the
geomembrane layer than would have
otherwise been possible. Additionally,
this eliminated the need for dewatering the sites prior to installing the system. Furthermore, the installation of the
geomembrane layer prevented further
recharge of precipitation into the waste
area, reducing the amount of water that
would ultimately be removed in comparison with the traditional approach.
Construction schedule
By choosing the TG-FCS versus the traditional method, the project team estimated
the reduction in project schedules to be
between 50% and 75%. The most significant contribution to the reduction of the
schedules was the ability to install the
impermeable layer without dewatering.
Once the structured geomembrane
was in place, the installation contractor
was able to install the engineered synthetic turf layer, followed by the specified infill component. All these activities
were completed without having the sites
dewatered first.
Additionally, by removing the soil
burden and associated equipment, the
construction schedules were not as
affected by adverse weather conditions
with the TG-FCS as they would have
been with the traditional method. With
the TG-FCS method, there is minimal

Geosynthetics August/September 2019

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