Geosynthetics October/November 2021 - 18

Using bentonite-polymer composite GCLs to contain CCR leachates
10-9
10-10
BP4.0
BP5.8
BP6.3
BP8.6
BP8.9
BP9.0
BP9.7
10-11
(a)
the highest hydraulic conductivities were
obtained for leachates with lower RMD
and lower anion ratio, and the lowest
polymer loading. The low RMD may
have suppressed swelling of the bentonite,
rendering the polymer loading insufficient
to achieve low hydraulic conductivity
for these more permeable BPC GCLs.
10-12
6a
10-9
(b)
10-10
BP4.0
BP5.8
BP6.3
BP8.6
BP8.9
BP9.0
BP9.7
10-11
10-12
6b
10-2
10-1
100
Cl-/SO4
101
2102
103
FIGURES
6a and 6b Hydraulic conductivity vs.
(6a) RMD and (6b) anion ratio of CCR leachates
10-12
10-11
10-10
10-9
10-8
10-7
10-6
BP4.0
BP5.8
BP6.3
BP8.6
BP8.9
BP9.0
BP9.7
NaB
02 468 10
Polymer Loading (%)
FIGURE 7 Hydraulic conductivity of BPC-GCLs
to CCR leachates as a function of polymer
loading. Data for NaB GCLs (closed symbols)
from Chen et al. (2019).
12
Tian et al. (2019) and Chen et al. (2019)
indicate that the hydraulic conductivity
of BPC GCLs is controlled by polymer
hydrogel clogging intergranular pores.
Higher polymer loading in the BPC GCL
provides greater likelihood that flow paths
are clogged and the hydraulic conductivity
is low. Hydraulic conductivity to the CCR
leachates is shown in Figure 7 as a function
of polymer loading of the BPC GCL
(open symbols). Hydraulic conductivities
of NaB GCLs in the figure are reported
as zero polymer loading (closed symbols).
As the polymer loading increases,
the maximum hydraulic conductivity of
the BPC GCL decreases, and the hydraulic
conductivities become increasingly
consistent. The hydraulic conductivity
is consistently less than 10-10 m/s when
the polymer loading exceeds 4%, and less
than 10-11 m/s when the polymer loading
exceeds 6%. The type of polymer used in
the BPC probably influences the threshold
as well, but was not provided by the GCL
manufacturers. These hydraulic conductivities
represent the equilibrium condition
obtained with the aforementioned
methods. In the long-term, polymer elution
may alter the hydraulic conductivity
of the BPC GCL (Tian et al. 2019).
Conclusion
Hydraulic conductivity tests were conducted
on seven BPC GCLs using seven
CCR leachates. The GCLs were permeated
18
Geosynthetics | October November 2021
10-3
10-2
10-1
RMD
100
101
Mechanisms controlling
hydraulic conductivity of
BPC GCLs to CCR leachate
directly with leachate (no prehydration) at
an effective stress of 2.9 psi (20 kPa). The
following conclusions are drawn:
* BPC GCLs can have appreciably lower
hydraulic conductivity than NaB GCLs
when permeated with CCR leachates.
The BPC GCLs evaluated in this study
have hydraulic conductivities to CCR
leachates ranging from 10-12 to 10-10
m/s, whereas NaB GCLs had hydraulic
conductivities to the CCR leachates
ranging from 10-10 to 10-6 m/s.
* BPC GCLs with higher polymer loading
tend to have lower hydraulic conductivity
to CCR leachates. BPC GCLs
consistently had hydraulic conductivity
less than 10-10 m/s when the polymer
loading was greater than 4%, and
less than 10-11 m/s when the polymer
loading was greater than 6%. Polymer
type likely affects these thresholds, but
was not explored in this study.
References
ASTM D5084. Standard test methods for measurement
of hydraulic conductivity of saturated porous materials
using a flexible wall permeameter, ASTM International,
West Conshohocken, Pa.
ASTM D6766. Standard test method for evaluation
of hydraulic properties of geosynthetic clay liners
permeated with potentially incompatible aqueous
solutions, ASTM International, West Conshohocken, Pa.
Benson, C., Chen, J., Likos, W., and Edil, T. (2018). " Hydraulic
conductivity of compacted soil liners permeated with coal
combustion product leachates. " Jour. of Geotechnical and
Geoenvironmental Engineering, 144(4), 04018011.
Bittner, A., Kondziolka, J., and Benson, C. (2019).
" Relative liner performance for coal combustion product
management sites: Conceptual review and model
evaluation for surface impoundments. " Electric Power
Research Institute (EPRI), Palo Alto, Calif.
Chen, J., Benson, C. H., and Edil, T. B. (2018). " Hydraulic
conductivity of geosynthetic clay liners with sodium
bentonite to coal combustion product leachates. " Jour.
of Geotechnical and Geoenvironmental Engineering,
144(3), 04018008.
Chen, J., Salihoglu, H., Benson, C. H., and Likos, W. J.
(2019). " Hydraulic conductivity of bentonite-polymer
geosynthetic clay liners to coal combustion product
leachates. " Jour. of Geotechnical and Geoenvironmental
Engineering, 145(9) , 04019038.
Di Emedio, G., Van Impe, W., and Flores, V. (2011).
" Advances in geosynthetic clay liners: Polymer enhanced
clays. " Proc., GeoFrontiers 2011, American Society of Civil
Engineers, Reston, Va., 1931-1940.
Hydraulic Conductivity (m/s)
Hydraulic Conductivity (m/s)
Hydraulic Conductivity (m/s)
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