Insight into hydraulic conductivity testing of geosynthetic clay liners (GCLs) exhumed after 5 and 7 years in a cover

Abstract

Four geosynthetic clay liners (GCLs) serving as single liners were exhumed from below 0.7 m of silty sand on a 3:1 (horizontal:vertical) north-facing slope at the QUELTS site in Godfrey, Ontario, after 5 and 7 years. The 300 mm GCL overlaps with 0.4 kg/m supplemental bentonite were all physically intact. The exchangeable bound sodium was completely replaced with divalent cations. The GCL with the smallest needle-punched bundle size (average of 0.7 mm) and percentage area covered by bundles (4%) maintained low hydraulic conductivity (k) when tested under 0.07-1.2 m head with 10 mmol/L CaCl 2 solution as the permeant. For GCLs with larger bundles (1.1-1.6 mm) and higher percentage area covered by bundles (9%-14%), k was low when the head was low (0.07 m). Once the applied head increased, k increased by 1-4 orders of magnitude depending on the (i) hydraulic gradient, (ii) size and number of the needle-punched bundles, and (iii) structure and mass of the bentonite per unit area. The results suggest that the GCLs can perform effectively as a single hydraulic barrier in covers providing that the head above the GCL is kept low (e.g., by a suitable drainage layer above the GCL).Key words: geosynthetic clay liner, cover, overlaps, cation exchange, hydraulic conductivity, field study. Résumé :Quatre couches d'argile géosynthétiques (CAG) agissant comme des parois uniques ont été exhumés d'une profondeur en dessous de 0,7 m sur un sable limoneux de 3 : 1 (horizontale : verticale) au versant nord au site QUELTS dans Godfrey, en Ontario, après 5 et 7 ans. Les 300 mm de CAG se superposent au 0,4 kg/m de bentonite supplémentaire qui est physiquement intact. Le sodium lié échangeable a été complètement remplacé par des cations divalents. Le CAG avec la plus petite taille de paquet aiguilleté (moyenne de 0,7 mm) et le pourcentage de la superficie couverte par des faisceaux (4 %) a maintenu une faible conductivité hydraulique (k) lors de l'essai sous une tête de 0,07 à 1,2 m avec une solution 10 mM de CaCl 2 comme perméant. Pour les CAG avec de plus grands faisceaux (1,1 à 1,6 mm) et un pourcentage plus élevé de la zone couverte par des faisceaux (9-14 %), k est faible quand la tête était faible (0,07 m). Une fois que la tête appliquée a augmenté, k a augmenté de 1 à 4 ordres de grandeur en fonction (i) du gradient hydraulique, (ii) du nombre et de la taille des faisceaux aiguilletés et (iii) de la structure et la masse de la bentonite par unité de surface. Les résultats suggèrent que le CAG peut fonctionner efficacement comme une seule barrière hydraulique dans des couvercles à condition que la tête au-dessus du CAG soit maintenue à un niveau bas (p. ex., par une couche de drainage approprié au-dessus du GCL). [Traduit par la Rédaction] Mots-clés : couche d'argile géosynthétique, couvercle, chevauchements, échange de cations, conductivité hydraulique, étude sur le terrain.

Uma abordagem geral dos principais fatores influenciadores no desempenho de geocompostos argilosos

“…As perfurações ocorridas seguem, em geral, o mecanismo de punção, fazendo com que a local onde desenvolvida se tornem pontos de alta permeabilidade. Nos casos da bentonita sódica, devido sua elevada expansão, esta possui a capacidade de auto reparação (ESTORNELL e DANIEL, 1992;BOARDMAN e DANIEL, 1996;DIDIER et al 2000;ROWE et al 2018). Didier et al (2000), por exemplo, mencionam que perfurações de até 30 mm são capazes de serem seladas após a hidratação do GCL e que, para tamanhos como estes, cerca de 15 dias são necessários.…”

Performances of the Soil–Bentonite Cutoff Wall Composited with Geosynthetic Clay Liners: Large-Scale Model Tests and Numerical Simulations

“…Previous researchers and participants have identified the critical role of the GCL overlap in maintaining the effective contaminant [4,5] and investigated the effects of contributing factors, namely, confining stress and supplemental bentonite applied at the overlap, on hydraulic performances of the GCL overlap [6]. Granular and powder bentonite ranging from 400 to 600 g/m are two common materials of supplemental bentonite in the application of bottom liners and cover systems [7][8][9][10]. Both materials may be unsuitable for improving the permeation of the cutoff wall considering that they tend to move downward under gravity.…”

Birim Alan Başına Bentonit Kütlesinin Geosentetik Kil Örtülerin (GKÖ’ler) Hidrolik İletkenliği Üzerine Etkisi

“…In this study, it is revealed that the hydraulic conductivity increases with an increase in the CaCl2 concentration. Rowe et al, 2017 carried out hydraulic conductivity tests on exhumed GCLs after 5 and 7 years in a cover. The authors investigated the effect of mass per unit area (MPUA) on the hydraulic conductivity of GCLs under different conditions.…”