Geosynthetics October/November 2019 - 16

Alternative coal ash pond closure design and construction

money associated with failed CQA testing
and repairs during construction.
Construction management services
can be performed by the owner, design
team or CQA team. On this project, the
owner performed some construction
management services while the CQA
team performed other construction
management services. This includes
managing the contractors on-site,
reviewing submittals, conducting safety
programs and addressing security issues.
Depending on the size and complexity of
the project, this may require a full-time
person devoted to construction management activities who reports to the owner.

Considerations

FIGURE 4 Epoxy mix being placed onto sand infill

There are two different ways to seam
the geotextile/turf component: stitching (Figure 5) and welding (Figure 6).
Most geosynthetic contractors are certified in only one of the two methods.

FIGURE 5 Geotextile component seaming using the sewing method
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Geosynthetics | October November 2019

While each method is approved by the
manufacturer for the structured geomembrane/turf component system and each
makes strong seams, there are differences
in timing and weather requirements to
consider before choosing a method. The
welding method uses the same welding equipment as for the geomembrane
liner but with some modifications and at
different settings. The welding method
does not require flipping the geotextile/
turf and allows for multiple consecutive
seams to be completed at the same time.
Unfortunately, welding is subject to the
same weather issues as geomembranes
and cannot be used on wet material. Since
the turf component can't be quickly wiped
dry, as can be done on the structured geomembrane, there may be longer delays
than expected for the turf component to
dry out. Stitching requires flipping the
turf component, sewing it together, then
unfolding the material. This typically
allows for fewer seams to be joined at the
same time, but this method can be done
on wet material. The stitching method also
keeps welding operators moving forward
in good weather while a small crew works
on the turf component behind the main
crew or in bad weather cycles.
Geomembranes are affected by
weather and will stretch or wrinkle in
warm weather and shrink in colder
weather. Therefore, another consideration is how to design the ditches so that
temperature differences do not affect
stormwater flow. This is an issue for any
geosynthetic exposed to varying temperature conditions. Though this is typically only an issue for low sloping ditches,
the effects of cold weather shrinking or
hot weather wrinkling the underlying
material is something to consider during
the design process in regions where there
are distinctly different summer and winter
weather conditions. This is a stone-lined
drainageway that does not require special mixes for the turf component infill.

Geosynthetics October/November 2019

Table of Contents for the Digital Edition of Geosynthetics October/November 2019