Conference PaperPDF Available

Interface Transmissivity of Multicomponent GCLs

August 2016

DOI:10.1061/9780784480168.070

Conference: Geo-Chicago 2016

Authors:

Ahmed Youssef Abdel Razek

Queen's University

Ronald Kerry Rowe

Queen's University

GCL Properties (all masses are dry mass)

…

Figures - uploaded by Ahmed Youssef Abdel Razek

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Content uploaded by Ahmed Youssef Abdel Razek

Content may be subject to copyright.

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Interface Transmissivity of Multicomponent GCLs

Ahmed AbdelRazek1 and R. Kerry Rowe2

1 Ph.D. Candidate, GeoEngineering Centre at Queen’s-RMC, Queen’s University,

Ellis Hall, Kingston ON, Canada, K7L 3N6. Email: Ahmed.abdel.razek@ queensu.ca.

2 Professor, Canada Research Chair in Geotechnical and Geoenvironmental

Engineering, GeoEngineering Centre at Queen’s-RMC, Queen’s University, Ellis

Hall, Kingston ON, Canada K7L 3N6. E-mail: kerry.rowe@queensu.ca.

ABSTRACT:

Both a coated and laminated GCL from the same manufacturer are examined with

respect to the interface transmissivity between the geofilm and a smooth 2.0 mm HDPE

GMB. The laboratory apparatus and test methods are described. The results obtained

from the interface transmissivity tests conducted under vertical stress of 150 kPa and

hydraulic head of 1.2 m are reported. The preliminary results suggest similar low

interface transmissivities to water of 1.2x10-11 m2/s and 1.3x10-11 m2/s for the coated

and laminated GCLs.

INTRODUCTION

Composite barrier systems are comprised of a geomembrane (GMB) overlying either

a compacted clay liner (CCL) or geosynthetic clay liner (GCL) or both. The primary

objective of the geomembrane is to prevent advective contaminant migration and, for

some contaminants, to also effectively prevent diffusive migration where the GMB is

intact. GCLs are intended primarily to reduce the leakage through GMB holes due to

its low hydraulic conductivity but the leakage will also be greatly related to the lateral

flow of contaminant away from the hole at the interface between the GMB and GCL

and this will depend primarily on the interface transmissivity between the GMB and

GCL (Fukuoka 1986, Brown et al. 1988, Rowe 1998, Mendes et al. 2010, Rowe et al.

2013).

Recently, multicomponent GCLs (coated and laminated GCLs) have been developed.

A coated GCL has a molten polyolefin layer applied to the carrier geotextile and

allowed to solidify. A laminated GCL has a thin geofilm glued to one side of the GCL.

In terms of hydraulic conductivity, they lie between a GMB and a conventional GCL

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(Cleary and Lake 2011; von Maubeuge et al. 2011; Barral and Touze-Foltz 2012).

Barral and Touze-Foltz (2012) proposed an experimental device to quantify the flow

rate through undamaged multicomponent GCLs. Examining four multicomponent

GCLs, they concluded that, for a geofilm with a high mass per unit area, the flow rate

of multicomponent GCLs is significantly smaller than that of conventional GCLs and

one order of magnitude greater than a virgin geomembrane. Whereas in the case of low

mass per unit area of geofilm, the hydraulic performance was closer to that of a

conventional GCL rather than virgin geomembrane due to the discontinuities

(imperfections) in the geofilm component of the GCL.

Several researchers have investigated the water transmissivity of a GMB/GCL

interface under various configurations, stress level and hydraulic heads (Harpur et al

1993; Barroso et al 2006, 2008, 2010; Bannour et al. 2013; Mendes et al. 2010, Rowe

and Abdelatty 2013) as summarized by Rowe (2012). Published data also suggests that

the GMB texture and nature of the bentonite had minimal effect on the interface

transmissivity under steady state conditions for the cases examined at 50 kPa applied

normal stress (Barroso et al 2008; Mendes et al. 2010).

Bannour and Touze-Foltz (2013) investigated the transmissivity at the interface

between the coating/laminate and the bentonite component of the GCL for three

different multicomponent GCLs of diameter 0.2 m using a decimeter scale cell (Touze-

Foltz et al. 2006). These tests, conducted under normal stress of 50 kPa and a hydraulic

head of 0.3 m, examined one coated GCL (GCL-T1) with a geofilm mass per unit area

of 0.25 to 0.4 kg/m2. The other two GCLs (GCL-T2 and GCL-T3) were both laminated

with a geofilm of about 0.2 kg/m2. Flow was introduced through a 4 mm prescribed

hole in the GCL coating and flow between the coating and the upper bentonite was

monitored. Two cases were examined: (i) no GMB placed on top of the punctured

geofilm component of the GCL, and (ii) GMB with hole directly over the hole in the

geofilm component of the GCL, silicone grease was applied on the bottom surface of

GMB to ensure that flow can only occur through the coating/attached film hole then

through the interface layer between coating/ attached film and upper bentonite of the

GCL. For the case of no GMB, the interface transmissivity values ranged from 3.5x10-

11m2/s (coated GCL-T1) to 5.5x10-10 m2/s (laminated GCL-T3). The case with an

overlying GMB resulted in an interface transmissivity ranging from 2.6x10-11 m2/s

(coated GCL-T1) to 4.4x10-11 m2/s (laminated GCL-T2) which is lower than the case

of no GMB, suggesting that the coating/film rigidity may lead to decreased flow rate

and interface transmissivity between the coating and the rest of the GCL.

Bannour and Touze-Foltz (2015) investigated the effect of scale on the flow rates of

multicomponent GCL. Tests were conducted using the same multicomponent GCLs

studied by Bannour and Touze-Foltz (2013) in a 1.0 meter diameter cell under same

test conditions (normal stress of 50 kPa and hydraulic head of 0.3 m). The only

difference was the use of protective geotextile of mass per unit area of 1.2 kg/m2 to

protect the coating from being punctured by a gravel layer placed over the geofilm

component of the GCL. One test was conducted for each of the three multicomponent

GCLs. An additional experiment was performed using GCL-T2 where the gravel was

placed, without a protective layer, directly on the coating to assess the effect of the

protective geotextile on the flow rate. It was reported that the protective geotextile had

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no effect on the transient and steady state flow rates. Interface transmissivity values of

2.0x10-11, 9.0x10-11, and 7.6 x10-11 m2/s were calculated for GCL-T1, GCL-T2 and

GCL-T3, respectively. The flow rates ranged from 4.6x10-12 to 3.0x10-11 m3/s for the

meter scale tests compared to flow rates of 1.5x10-11 to 2.8x10-10 m3/s for the decimeter

scale (other test condition being similar) at steady state. This suggests that the larger

meter scale tests reduced preferential paths related to irregularities in contact conditions

and also, possibly, the effect of the edges in decimeter scale tests and decreased the

deduced transmissivity somewhat compared to the smaller scale tests. The flow rates

at the interface between the geofilm and the rest of the GCL in the meter scale tests

(4.6x10-12 to 3.0x10-11 m3/s) were similar to a conventional GCL in contact with GMB

(4.x10-12 m3/s) and within the range for the GMB/GCL interfaces examined by Touze-

Foltz and Barroso (2006).

While the work cited above has examined the interface between the geofilm and the

bentonite component of the GCL, the transmissivity of an equally important interface

between the GMB and geofilm has not been examined. Thus, the objective of this paper

is to describe a different apparatus for measuring interface transmissivity of

multicomponent GCL in contact with HDPE GMB. Two tests are presented to examine

the interface transmissivity of a coated and laminated GCL in direct contact with a

smooth 2.0 mm thick HDPE GMB at a normal stress of 150 kPa to simulate the stress

under 10 to 15m of waste.

LABORATORY SET-UP

The laboratory set-up was designed to simulate a composite liner comprised of an

HDPE geomembrane (GMB) overlying a multicomponent geosynthetic clay liner

(GCL). The configuration was inverted compared to the typical field condition. The

test cell comprised a 0.2 m internal diameter, 15 mm wall thickness, and 0.11 m high

polyvinyl chloride (PVC) cylinder. The test set-up (Figure 1) involved (from bottom

up) a 2.0 mm HDPE GMB (MxC20) with a 10 mm hole in its center glued to the bottom

of the cell. The GCL was pre-hydrated with deionized water and cut to a diameter of

0.2 m. keeping the cover geotextile, a 25 mm ring of the carrier geotextile and bentonite

around the entire perimeter of the GCL was removed to create a space for the gravel

filter as shown in Figure 1. A geotextile strip having a thickness equal to the thickness

of bentonite and the carrier geotextile was placed around the bentonite. The GCL was

placed on the GMB with the laminated/coated carrier geotextile facing the GMB.

Fine gravel (4.75 mm < D < 5.6 mm) was placed around the GCL to transmit interface

flow to the effluent valve (Figure 1). A rubber bladder was placed on the top of GCL.

Bentonite paste was used to seal the edges of the bladder to the walls of the PVC cell.

Sand was used to fill the cell from the top of bladder to the top cap of the PVC cell.

The sand had a maximum dry density of 1.7 Mg/m3 at a moisture content of 12%. The

permeant was introduced to the cell through an influent valve at the bottom of the cell.

Whereas the effluent was collected in 250 mL HDPE capped bottle (with a thin air

pressure equilibration tube) through a lateral valve at the level of interface between the

GCL and GMB. A control collection bottle showed negligible evaporation of effluent

at room temperature in the laboratory.

Page 4

An upper gravel layer (Figure 1) was used as a detection layer to indicate if there was

any leakage between the bladder and the cell walls. A port was located at the mid height

of the gravel layer to monitor any such leakage (none was detected).

Air pressure was applied through the main pressure line with a regulator to control

the pressure to the desired value. The hydraulic head causing interface flow was applied

through 1000 ml graduated cylinder connected to the cell through a flexible tube with

water stopper placed on top of the cylinder to control the influent evaporation (but with

a thin pressure equilibration tube). For the tests reported herein, a hydraulic head of

1.2 m and a vertical stress of 150 kPa were applied to simulate a landfill that contains

waste of an average height 10 to 15 m (depending on waste density).

FIG. 1. Laboratory set-up for measuring interface transmissivity between a

GMB and GCL.

GCL

Two GCLs were examined. GCL-A (Bentofix CNSL) was a coated needle-punched

GCL comprised of 3.77 kg/m2 fine granular natural sodium bentonite between a staple

fiber needle-punched nonwoven cover geotextile (280 g/m2) and a woven carrier

geotextile with a polypropylene coating (combined mass per unit area of 350 g/m2; the

coating was so well bonded to the geotextile it was not possible to separate and

independently assess the mass of the two components). GCL-B (Bentofix LNSL) was

a laminated GCL comprised of 3.89 kg/m2 fine granular natural sodium bentonite

between a staple fiber nonwoven cover geotextile (288 g/m2) and a woven carrier

geotextile (145 g/m2) with an about 0.2 mm thick (170 g/m2) polyethylene film glued

to the woven geotextile (Table 1). Figure 2a and 2b show the top view and cross section

Leak

Detection

Valve

Effluent

Valve

GMB

Influent Valve

GCL with coating/laminate in

contact with GMB

Gravel

Compacted Sand

Gravel

Compacted Sand

Pneumatic Pressure

Fixed

Head

Tank

H (m)

Bladder

Bentonite

Paste

GTX

strip

Page 5

(with bentonite shaken out) view of GCL-A and GCL-B respectively.

Both GCLs were pre-hydrated prior to placement in the cell with deionized water for

two days (100% gravimetric water content) to provide initial GCL hydration that might

simulate a relative high degree of hydration from the subsoil in the field before

permeating fluid reached the hole in the geomembrane.

Table 1. GCL Properties (all masses are dry mass)

Generic

identifier

Average dry

mass of

GCL1

(g/m2)

Average

dry mass

of carrier

geotextile1

(g/m2)

Average

dry mass

of cover

geotextile1

(g/m2)

Average

dry mass

bentonite1

(g/m2)

Geofilm

thickness

(mm)

Average

dry

mass of

geofilm

(g/m2)

GCL-A

4410 ± 143

350a

280c

3770

- a

GCL-B

4520 ± 545

145b

288c

3890

0.2

170

ASTM

D5993

D5261

D5993

D5199

D5261

1Average of five virgin GCL samples each 100 x 100 mm, taken from the same area

on the GCL roll.

a Woven geotextile with geofilm coating that could not be separated for independent

measurement

b Woven GTX to which laminate had been attached was easily separated allowing

measurement of both independently.

c Needle-punched nonwoven geotextile

(a) (b)

FIG. 2. Photographs of multicomponent GCLs (a) GCL-A (b) GCL-B.

Page 6

RESULTS AND DISCUSSION

Inflow rates were measured by monitoring the volume change of water in the burette

used to monitor inflow over prescribed time intervals (as in falling head test). Eq. 1 was

used for calculate the interface transmissivity (Harpur et al. 1993).

=a.ln(R2

R1)ln(h2

h1)

2t (1)

where:

 = interface transmissivity (m2/s)

h = difference between head at hole and head at specimen boundary (m)

R2 = outer radius of specimen (m)

R1 = hole radius (m)

a = cross sectional area of falling head burette (m2)

h2 = head at the end of monitoring interval (m)

h1 = head at start of monitoring interval (m)

t = monitoring time interval (s)

Figure 3 shows the interface transmissivity values versus time for GCL-A (coated

GCL) as calculated using Eq. 1. The transmissivity dropped over time from 7x10-11

m2/s after 5 hours to 5.9x10-12 m2/s after 22 days and increased to 1.2x10-11 m2/s at 43

days after test initiation. The test is still in progress.

FIG. 3. Interface transmissivity versus time for coated GCL-A

GCL A

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For the laminated GCL-B, the interface transmissivity values decreased from

7.7x10-11 m2/s after 11 hours of test initiation to 1.3x10-11 m2/s after 43 days (Figure 4).

FIG. 4. Interface Transmissivity versus time for laminated GCL-B

AbdelRazek et al. (2016) reported that after 300 days of testing, the interface

transmissivity of a smooth 1.5 mm-thick HDPE geomembrane (MxC15) with a GCL

having powdered sodium bentonite was 9 x 10-13 m2/s and that with a GCL having a

granular sodium bentonite was 5 x 10-13 m2/s at 150 kPa. These values are lower than

the interface transmissivity of the GMB with the coated (1.2x10-11 m2/s; Figure 3) and

laminated (1.3x10-11 m2/s; Figure 4) GCLs. There are some factors thought to be

affecting the interface transmissivity values obtained for the granular and powdered

sodium bentonite at 150 kPa including the time dependent uptake of moisture and

intrusion of bentonite into the cover geotextile over the 300 days these test were

conducted which serve to reduce the interface transmissivity with time (AbdelRazek et

al. 2016). In contrast, the interface transmissivity values for the coated (1.2x10-11 m2/s)

and laminated (1.3x10-11 m2/s) GCLs reported above were similar to but slightly lower

than the values reported by Bannour and Touze Foltz (2013) where the interface

transmissivity values between coating/ attached film and upper part of bentonite for the

case of GMB were 2.6x10-11 m2/s and 4.4x10-11 m2/s respectively under 50 kPa and

hydraulic head of 0.3m. The difference in transmissivity values reported herein and the

study conducted by Bannour and Touze Foltz (2013) can be attributed to the difference

between transmissivity of GMB and the coating/ attached film to transmissivity

between coating/attached film and upper part of bentonite. When dealing with

transmissivity of multicomponent GCLs, two interface layers should be considered;

first, the interface between the coating and GMB, second, the interface between the

coating and bentonite component of the GCL (Rowe 2016). It is hypothesized that, for

the aligned holes of GMB and geofilm, the transmissivity between the coating and

GCL B

Page 8

bentonite component would govern the leakage estimation. Further research is currently

carried out to examine the performance of multicomponent GCLs with

damaged/undamaged geofilm in contact with GMB to assess the interface

transmissivity for geofilm/bentonite and GMB/geofilm. Also the test result reported in

this paper for the coated and laminated GCL in contact with a GMB were slightly lower

but similar to the interface transmissivity for conventional GCLs in contact with GMB

which is usually in range of 2-4x10-11 m2/s. The much lower values reported

AbdelRazek et al. (2016) may be due to the greater bentonite movement that could

occur in those tests with time over the 300 days of those tests.

CONCLUSIONS

The procedure developed for measuring interface transmissivity has performed well

for multicomponent GCLs with an undamaged geofilm placed in contact with HDPE

GMB.

The preliminary interface transmissivity values to water obtained for the coated and

laminated GCLs were both low at 1.2x10-11 m2/s and 1.3x10-11 m2/s, respectively after

43 days of testing at 150 kPa. These values are broadly in line with, or lower than, the

interface transmissivity values of GMB with conventional GCLs. This finding is

subject to further confirmation as the tests continue over longer period of time.

Other factors not considered here that may also potentially affect the interface

transmissivity include the presence of imperfections in the coating, alignment of the

GMB puncture with a coating imperfection, geomembrane roughness, and performance

at low stress levels. More work is needed to fully understand the interactions occurring

at the GMB/GCL interface with time.

ACKNOWLEDGMENTS

The research reported in this paper was supported by a Natural Sciences and

Engineering Research Council of Canada (NSERC) grant (A1007) to Dr. R.K. Rowe.

The equipment used was funded by Canada Foundation for Innovation (CFI) and the

Government of Ontario Ministry of research and Innovation.

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20ICSMGE Vol 2 General

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Waste disposal facilities commonly have a composite liner (e.g., a geomembrane, GMB, over a geosynthetic clay liner, GCL) in both the cover and bottom liner. The performance of a composite liner primarily depends on the size, number, and location of holes in the geomembrane together with the hydraulic conductivity, k, of the GCL, and the interface transmissivity, between the GMB/GCL interfaces. In many parts of the world a composite liner in a cover may be subject to freeze-thaw conditions. This is particularly true for covering of mine and other wastes in the Arctic and for the remediation of contaminated soil at bases in Antarctica. A preliminary study was conducted to assess the effect of permeant solutions when a GMB/GCL interface was frozen and thawed for 5 and 16 freeze-thaw cycles on for a range of stresses (10-25 kPa) typical for cover applications. The preliminary results show that for RO water as a permeant fluid, there was no significant effect on transmissivity of 5 freeze-thaw cycle but there was an effect after 16 cycles. When water with 260 mg/L calcium was the permeant, there was an increase in transmissivity for both 5 and 16 freeze-thaw cycles. A comparison is also made with results from an open system where cryosuction can draw moisture from the subgrade and the implications are discussed. RÉSUMÉ : Les installations d'élimination des déchets ont généralement une doublure composite (par exemple, une géomembrane, GMB, sur une doublure d'argile géosynthétique, GCL) à la fois dans la couverture et la doublure inférieure. Les performances d'un revêtement composite dépendent principalement de la taille, du nombre et de l'emplacement des trous dans la géomembrane ainsi que de la conductivité hydraulique, k, du GCL, et de la transmissivité de l'interface, , entre les interfaces GMB / GCL. Dans de nombreuses régions du monde, un revêtement composite dans une couverture peut être soumis à des conditions de gel-dégel. Cela est particulièrement vrai pour le recouvrement des mines et autres déchets dans l'Arctique et pour l'assainissement des sols contaminés dans les bases de l'Antarctique. Une étude préliminaire a été menée pour évaluer l'effet des solutions de perméation lorsqu'une interface GMB / GCL a été congelée et décongelée pendant 5 et 16 cycles de gel-dégel sur pour une gamme de contraintes (10-25 kPa) typiques des applications de couverture. Les résultats préliminaires montrent que pour l'eau RO en tant que fluide perméant, il n'y avait pas d'effet significatif sur la transmissivité de 5 cycles de gel-dégel, mais il y avait un effet après 16 cycles. Lorsque l'eau contenant 260 mg / L de calcium était le perméant, il y avait une augmentation de la transmissivité pour les cycles de 5 et 16 cycles de gel-dégel. Une comparaison est également faite avec les résultats d'un système ouvert où la cryosuccion peut aspirer l'humidité de la plate-forme et les implications sont discutées.

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Recently, there has been increased interest in the use of geosynthetic clay liners (GCL) in composite liners in harsh environments like the Arctic and Antarctic regions. The primary role of a GCL in the composite liner is to minimize the advective flow of contaminants if there are any holes in the geomembrane (GMB). The two parameters controlling the effectiveness of this composite system are the hydraulic conductivity, k, of the GCL and interface transmissivity, θ, between the GMB and GCL. This paper reports results from a preliminary study of a “closed system” approach to subjecting specimens to freeze-thaw cycles by putting them in and out of a freezer and an “open system” where the specimen remains in contact with the subgrade under an applied stress during 5-freeze-thaw cycles. Attention is focused on the effect of these two methods on interface transmissivity for a range of stresses typical for cover applications. The preliminary results shows that the “open system” during freeze-thaw cycles allowed the formation of an ice lens at the GMB-GCL interface due to cryosuction, and this increased θ at a low stress of 10 kPa compared to using the “closed system.”

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Article

Sep 2022

An experimental study of the effect of closed system and a limited study of open system freeze-thaw cycles on the interface transmissivity at applied stresses between 10 and 150 kPa is described. The effect of closed system freeze-thaw is most apparent after 100 freeze-thaw cycles and permeation at a stress ≤25 kPa. The effect of permeating fluid chemistry is also evident but decreased with increasing stress. One notable effect of permeant is the potential for internal erosion along weaknesses in the bentonite created by freeze-thaw cycles when permeated by distilled or reverse osmosis water. This is not observed when permeated with simulated porewater containing cations. In terms of practical application, closed system freeze-thaw cycles appear to have little effect on interface transmissivity, and to the extent that there is an effect, it is beneficial. In contrast, cryogenic suction arising with open system freeze-thaw cycles is shown to result in the formation of ice lenses both within the GCL and at the GCL geomembrane interface. Although limited, the data suggest that the effect of ice lens formation on interface transmissivity after open system freeze-thaw cycles is largely eliminated at applied stress above 20-25 kPa, although more research is warranted.

Performance of GCLs after long term wet-dry cycles under a defect in GMB in a landfill

Article

Feb 2022

Two GCLs with sodium bentonite and three GCLs with polymer amended bentonite were subjected to wet-dry cycles selected to simulate the conditions to which a GCL on an 18 o slope might be subjected: for a GCL below an exposed geomembrane wrinkle with a hole. The wetting involved water flowing over the GCL for 8 hours each cycle. Three drying cycles (0.67, 7, and 14 days) were examined. After 12-18 months of wet-dry cycles, the samples were x-rayed to identify representative specimens for testing. The changes in the hydraulic conductivity, k, of the GCLs were obtained when permeated with two synthetic municipal solid waste leachates at an applied head of 0.35 m for a range of effective stresses (3 - 150 kPa). The results showed an up to a four order of magnitude difference in k depending on applied stress and RMD of the leachate permeant. The effects of the number and the duration of the wet-dry cycles, the GCL mass per unit area, presence/absence of polymer modification, the carrier geotextile, the number and the size of the needle punch bundles, and the bundle thermal treatment are discussed.

Factors affecting Multicomponent GCL-Geomembrane Interface Transmissivity for Landfills

Article

Dec 2020

A series of laboratory tests were conducted to investigate the interface transmissivity, θ between a 1.5 mm thick high-density polyethylene geomembrane (GMB) and a multicomponent geosynthetic clay liner (MC_GCL) when permeated with a simulated municipal solid waste landfill leachate under a range of applied stresses (10-150 kPa). The effect of three different prehydration fluids, a 4-mm diameter central coating defect, coating defect position, and the effect of coating orientation of the GCL were investigated. It was found that at an applied stress of less than 70 kPa, the effect of these factors on θ was largely masked by the variability in the initial interface contact condition between the GMB and GCL. At 100-150 kPa, the effects of initial variability were largely eliminated, but there was no notable effect of other factors for multicomponent GCLs on interface transmissivity.

Effect of interface transmissivity and hydraulic conductivity on contaminant migration through composite liners with wrinkles or failed seams

Article

Dec 2018

Effect of interface transmissivity and hydraulic conductivity on contaminant migration through composite liners with wrinkles or failed seams

Article

Full-text available

Dec 2018

The leakage and the peak chloride concentration in an aquifer for a single composite liner facility is modelled for (i) a hole in a geomembrane wrinkle and (ii) a failed seam. A method using a closed-form solution to calculate leakage together with a l½-dimensional (l½D) semi-analytic contaminant transport model is proposed, and the results compared with those obtained from two-dimensional (2D) finite element modelling (FEM). Leakage is shown to be highly dependent on the interaction between the interface transmissivity (θ) and hydraulic conductivity beneath the wrinkle (kb). Similar leakages arising from different combinations of transmissivity and hydraulic conductivity are shown to have significantly different impacts on an underlying aquifer. Contaminant transport modelling is needed to assess this effect for the likely range of uncertainty regarding interface transmissivity (θ) and hydraulic conductivity. The 2D FEM is conceptually more comprehensive; however, using conventional software only a very limited size of problem could be accurately modeled given the greatly different scales that must be modelled. In contrast, the semi-analytic 1½D approach readily allowed consideration of the highly variable scales, and gave results at the down-gradient edge sufficiently similar to the 2D approach.

Roles of interface transmissivity and hydraulic Conductivity in limiting contaminant migration through composite liners

Conference Paper

Full-text available

Oct 2017

Geomembrane (GMB) are often used in conjunction with a geosynthetic clay liner (GCL), compacted clay liner (CCL), or both to form a composite liner for a wide range of hydraulic containment applications, including landfill liners, surface impoundments (e.g., ponds, lagoons), tailings storage facilities, and heap leach pads to minimize leakage. Often, they must act as a composite with a clay liner whose primary purpose is to minimize leakage through the holes in the GMB. Winkles in a GMB are a primary factor influencing leakage through a composite liner. Potentially, equally important is seam failure. This paper explores how the hydraulic conductivity of a GCL (k) and the interface transmissivity (θ) between GMB and GCL affects leakage in different scenarios either for a wrinkle with a hole or a failed seam. Consideration is given to landfill liners (high and low stresses) permeated with different types of leachates. The results highlighted the significance of interface transmissivity (θ) to the estimated leakage as well as the leachate-GCL chemical interaction on the flow parameters, hence the calculated leakage and contaminant concentration at aquifer levels.

Flow-rate measurements in meter-size multicomponent geosynthetic clay liners

Article

Full-text available

Feb 2015

To quantify the flow rate through multicomponent geosynthetic clay liners (GCLs), three different meter-sized specimens from different manufacturers were characterized in a dedicated experimental column. This study allows quantification of the interface transmissivity of multicomponent GCLs when the coating or attached film is damaged over an area large enough to make edge effects negligible. For all multicomponent GCLs characterized, the coating or attached film was less than 0.7 mm thick. Steady-state results indicated flow rates ranging from 4.61 × 10−12 to 3.01 × 10−11 m3/s with interface transmissivities ranging from 1.20 × 10−11 to 7.59 × 10−11 m2/s, which are broadly in line with flow rates obtained from conventional geomembrane (GM)–GCL composite liners. Consequently, when the coating or attached film is damaged, the thickness and rigidity of the coating or attached film appears not to affect the steady-state flow rate and interface transmissivity, which leads to a good contact at the interface.

Short- and long-term leakage through composite liners. The 7th Arthur Casagrande LectureThis lecture was presented at the 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, Toronto, Ont., October 2011, and a pre-print appeared in the conference proceedings.

Article

Full-text available

Jan 2012

Ronald Kerry Rowe

The factors that may affect short-term leakage through composite liners are examined. It is shown that the leakage through composite liners is only a very small fraction of that expected for either a geomembrane (GM) or clay liner (CL) alone. However, the calculated leakage through holes in a GM in direct contact with a clay liner is typically substantially smaller than that actually observed in the field. It is shown that calculated leakage taking account of typical connected wrinkle lengths observed in the field explains the observed field leakage through composite liners. Provided that care is taken to avoid excessive connected wrinkle lengths, the leakage through composite liners is very small compared to a typical GM or CL alone. It is shown that the leakage through composite liners with a geosynthetic clay liner (GCL) is typically much less than for composite liners with a compacted clay liner (CCL). Finally, factors that will affect long-term leakage through composite liners are discussed. It is concluded that composite liners have performed extremely well in field applications for a couple of decades and that recent research both helps understand why they have worked so well and provides new insight into issues that need to be considered to ensure excellent long-term liner performance of composite liners — especially for applications where the liner temperature can exceed about 35 °C.

Flow Rate Measurement in Multi-Component Geosynthetic Clay Liners

Chapter

Full-text available

Jul 2013

procedure was developed that combines measuring devices from NF EN 14150 for flow rate measurement through geomembranes and a rigid wall permeameter from NF P84-705. The new procedure aims at meas- uring flow rates through geosynthetic clay liners (GCLs) in order to measure flow rates through multi-component GCLs. The resulting testing device allows one to measure very small variations in volume with time while applying constant hydraulic pressures. The pressure difference applied on both sides of the multi- component GCL specimens varied between 25 kPa and 100 kPa, with the latter value being equal to the one applied across geomembranes in NF EN 14150. Three different multi-component GCLs from two different manufacturers were tested in order to determine the ability of the testing equipment to quantify the flow rate through multi-component GCLs. The flow rate measurement was performed after a hydration phase under very low hydraulic head and with a 10 kPa normal load on the specimens in accordance with NF P84-705. Details regarding the experimental conditions that could lead to the development of a standard for the measurement of flow rates through multi-component GCLs are given. Results obtained tend to show that flow rates are 1 order of magnitude larger than the ones usually measured for virgin geomembranes (i.e., 10exp�5 m3/m2/d).

Interface Transmissivity Measurement in Multicomponent Geosynthetic Clay Liners

Chapter

Full-text available

Jul 2013

Three different multicomponent geosynthetic clay liners (GCLs) from different manufacturers are tested in a transmissivity cell with a new testing procedure to quantify the flow rate and the interface transmissivity between the coating or attached film presenting a hole and the upper geotextile of the GCL. The testing device was previously used in studies aiming to evaluate the interface transmissivity between a damaged eomembrane (GM) and a regular GCL. Different results are obtained regarding the evolution with the time of the flow rate ranging from 1.73� 10-m3/s to 2.18� 10-�10 m3/s at steady state, which is on average in the range of flow rate results obtained with a GM–GCL composite liner. Additional tests performed by adding a GM on top give lower values of flow rates. This shows the importance of the film or coating rigidity for decreasing flow rate and insuring a better quality contact at the interface.

Leakage through liners constructed with geomembranes—Part II. Composite liners

Article

Full-text available

Dec 1989
GEOTEXT GEOMEMBRANES

This study of the mechanisms of leakage shows that a composite liner consisting of a geomembrane on low-permeability soil is most effective in reducing leakage through a liner.

Leakage and Contaminant Transport through a Single Hole in the Geomembrane Component of a Composite Liner

Article

Mar 2013

The migration of contaminants through a 10-mm-diameter hole (0.785 cm(2)) in a geomembrane in direct contact with a geosynthetic clay liner (GCL) and adjacent silty sand is examined. Experiments were conducted in four 0.6-m-diameter cells at a vertical stress of 100 kPa and hydraulic head differences of 0.3 and 1m. The system was first permeated with distilled water until steady-state flow was attained (the reference case). After 280 days the permeant was changed to a NaCL solution. After 800 days of permeation with 0.14 M NaCl solution there was only a 3% increase in the flow (leakage) compared with the reference case despite up to almost an order of magnitude increase in GCL permeability near the hole. The wetted radius at the end of the experiments was inferred by injection of dye and was found to be about 0.1-0.15 m. This provides the first experimental evidence in support of theoretical predictions that, when the geomembrane is in direct contact with a GCL, leakage through a hole is primarily controlled by the interface transmissivity rather than the GCL hydraulic conductivity when there is interaction between the permeant and the GCL. The observed chloride distribution in the silty sand at the end of the experiments is reported. DOI: 10.1061/(ASCE)GT.1943-5606.0000773. (C) 2013 American Society of Civil Engineers.

Flow rate measurement in undamaged multicomponent geosynthetic clay liners

Article

Dec 2012

The objective of the paper is the presentation of a test method to quantify advective flow rates through multicomponent geosynthetic clay liners (GCLs). A procedure was developed, combining measuring devices from EN 14150 for flow rate measurement through geomembranes and a rigid wall permeameter from NF P 84-705 aiming at measuring the flow rates through GCLs. Multicomponent GCLs by structure fall between geomembranes and GCLs. The resulting testing device allows measurement of very small variations of volume with time while applying constant hydraulic pressures. The pressure difference applied on both sides of the multicomponent GCL specimens varied between 25 kPa and 100 kPa, the latter value being equal to that applied across geomembranes in EN 14150, except in one case where the multicomponent liner had a light coating. In this case hydraulic heads of 0.3 and 0.6 m were applied. Four different multicomponent GCLs were tested, from three different manufacturers, in order to determine the ability of the testing equipment to quantify the flow rate through multicomponent GCLs. The flow rate measurement was performed after a hydration phase under a very low hydraulic head and a 10 kPa normal load on the specimens in accordance with NF P 84-705. Details are given of the experimental conditions that might lead to the development of a standard for the measurement of flow rates through multicomponent GCLs. Results obtained tend to show that flow rates are one order of magnitude larger than those usually measured for virgin geomembranes, that is 10-5 m(3)/(m(2) d), except for one of the multicomponent GCLs for which the light coating resulted in larger flow rates, measured with hydraulic heads of 0.3 and 0.6 m. In this case values consistent with previous values from the literature in the range 1.4 x 10(-11) m/s to 2.2 x 10(-11) m/s were obtained.

Long-term performance of contaminant barrier systems

Article

Jan 2005

Ronald Kerry Rowe

This lecture describes the latest findings with respect to the long-term performance of modern municipal solid waste (MSW) landfill barrier systems. Field data relating to the clogging of leachate collection systems and the latest techniques for predicting their performance are examined. It is indicated that the primary leachate collection systems may have service lives that range from less than a decade to more than a century, depending on the design details, waste characteristics and mode of operation. Recent data indicate that landfill liner temperatures can be expected to reach at least 30-40 degrees C for normal landfill operations. With recirculation of leachate the liner temperature increases faster than under normal operating conditions, and may be expected to exceed 40 degrees C. Temperatures (up to 40-60 degrees C) may occur at the base of landfills where there is a significant leachate mound. Temperature is shown to have a significant impact on both contaminant migration and the service life of the liner system. Field measurements and theoretical calculations show that composite liners are substantially better than single liners in terms of controlling leakage from landfills. Also, the leakage rates with a composite liner are very small, and diffusion will dominate as a transport mechanism for contaminants that can readily diffuse through a geomembrane (GM). Composite liners involving a GM over a geosynthetic clay liner (GCL) gave rise to substantially less leakage than those involving a compacted clay liner (CCL). The observed leakage through composite liners can be explained by the holes in, or adjacent to, wrinkles/waves in the GM, and this leakage can be calculated using simple equations. High-density polyethylene (HDPE) GMs provide an excellent diffusive barrier to ions. However, some organic compounds readily diffuse through HDPE GMs, and a combination of GM and an adequate thickness of liner and attenuation layer are required to control impact to negligible levels. The long-term performance of HDPE GMs is discussed. Based on the currently available data, the service life for HDPE GM in MSW landfill is estimated to be about 160 years for a primary liner at 35 degrees C and greater than 600 years for a secondary GM provided it is at a temperature of less than 20 degrees C. Clay liners are susceptible to both shrinkage and cracking during construction (due to heating by solar radiation or freezing) and after placement of the waste (due to temperature gradients generated by the waste). The former can be controlled by quickly covering the liner with a suitable protection layer. The latter can be controlled by appropriate design. The use of numerical models for predicting the service lives of engineered systems and long-term contaminant transport is demonstrated.

Empirical equations for calculating the rate of liquid flow through GCL-geomembrane composite liners

Article

Jan 2006

This paper presents equations for the evaluation of advective flow rates though composite liners involving GCLs. Advective flow is due to the existence of defects in the geomembrane, and depends on the contact condition between the geomembrane and the GCL. In this paper the geomembrane - geosynthetic clay liner contact condition is quantitatively defined, based on experimental data. Accordingly, empirical equations are presented for circular defects having diameters in two different ranges: 2 to 20 mm and 100 to 600 mm. The validity of the empirical equation obtained for the smallest range of diameters is compared with experimental results and with an existing empirical equation. The empirical equations developed in this paper are then combined in a simple analytical solution, leading to semi-empirical equations that allow one to predict flow rates for narrow and wide defects, taking account of the flow that takes place at both ends of these defects of finite length. A parametric study shows, through a correlation factor, the importance of the flow at both ends of defects of finite length, mainly for narrow defects.

Hydraulic and mechanical behavior of GCLs in contact with leachate as part of a composite liner

Article

Jun 2006
GEOTEXT GEOMEMBRANES

When a geosynthetic clay liner (GCL) containing sodium bentonite is brought into contact with fluids and soils containing other cations, the latter may exchange with the sodium present between clay layers. This modification of clay surface chemistry may change the clay microstructure and its mechanical behavior. The influence of cation exchange on the potential for squeezing of bentonite was studied by submitting 10-cm-diameter GCL samples to squeezing tests. Those samples were part of 1-m-diameter GCL specimens that had intentionally been put in contact with leachate during a one year period through the discontinuity in a damaged geomembrane as part of a composite bottom liner, and an underlying soil containing calcium, thus generating cation concentration gradients through the GCL specimens. The impact of the hydration mode of the GCL on flow rate through the composite liner and cation exchange was studied. Results obtained tend to show that if pre-hydration of GCL on the whole surface under no load as compared to pre-hydration through the discontinuity in the geomembrane slightly prevented from cation exchange, it resulted in a larger flow rate in the composite liner. Consequently, based on the experiments presented in this paper, pre-hydration of GCLs prior to confining is discouraged. Furthermore, an increase in the calcium concentration combined with a decrease in potassium and ammonium concentrations at the surface of clay particles lead to a softening of bentonite resulting in a greater susceptibility to bentonite squeezing in the GCL samples.

Interface Transmissivity of Multicomponent GCLs

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