Evaluation of a compacted till liner test pad constructed over a granular subliner contingency layer

Abstract

The construction and evaluation of a compacted clayey till test pad constructed over a stone layer are described. The evaluation of the clayey liner involved (i) excavation of six test pits through the liner, followed by careful visual inspection for defects in the liner; (ii) sampling of the liner using standard 75 mm diameter Shelby tubes, a 150 mm diameter piston sampler, and block sampling; (iii) triaxial hydraulic conductivity tests on samples of liner material consolidated to a number of stress levels relevant to the proposed design; and (iv) diffusion tests on samples of liner material. Based on the results it is concluded that it was possible to construct a low-permeability liner (hydraulic conductivity less than 1.4 X cm/s under expected field stress conditions). Geotextiles from above and below the compacted liner were carefully exhumed and subjected to a series of laboratory tests to examine (i) the effect of construction damage on the geotextile's strength; (ii) the effectiveness of the geotextile to minimize intrusion of the clay liner through the geotextile and into the stone layer(s) under expected field stress conditions; (iii) the effectiveness of the geotextile as a filter for the compacted liner material under high upward gradient conditions; and (iv) the friction angle between the geotextile and clay, and geotextile and stone. The geotextiles exhumed from the test liner showed some evidence of construction damage; however, based on the field observations and subsequent laboratory tests, it is concluded that they performed adequately.La construction et 1'Cvaluation d'une planche d'essai en till argileux construite sur une couche de pierres sont dCcrites. L'Cvaluation de la membrane argileuse impliquait : (i) l'excavation de six puits d'essai B travers la membrane suivie d'une inspection visuelle attentive pour identifier des dCfauts dans la membrane; (ii) I'Cchantillonnage de la membrane au moyen de tubes Shelby standard de 75 mm de diambtre, d'un Cchantillonneur B piston de 150 mm, et de blocs; (iii) des essais de conductivitk thermique dans un appareil triaxial sur des Cchantillons du rnatkriau de la membrane consolidCs B un certain nombre de niveaux de contraintes correspondant B la conception proposCe;(iv) des essais de diffusion sur des Cchantillons du matCriau de la membrane. En partant de ces rCsultats, il est conclu qu'il Ctait possible de construire une membrane de faible permCabilit6 (conductivitC hydraulique infkrieure B 1,4 X mls sous des conditions de contraintes prCvues sur le terrain). Des gCotextiles placCs dessus et dessous la membrane compactie ont Ct C exhumCs avec grand soin et soumis B une sCrie d'essais de laboratoire pour examiner : (i) l'effet du dommage dO B la construction sur la rCsistance du gCot extile : (ii) I'efficacitC du gCotextile pour minimiser l'intrusion de la membrane argileuse B travers le gCotextile et dans la ou les couches de pierres dans des conditions de contraintes prCvues sur le terrain; (iii) I'efficacitC du gkotextile comme filtre pour le matCriau...

Geochemical and transport properties of dissolved organic carbon in a clay‐rich aquitard

“…Thick clay‐rich aquitard systems are of interest to both industry and government because of their potential for geological storage of toxic wastes and for their role as protective covering for regional aquifer systems [ Hendry and Wassenaar , 1999]. Because of their extremely low hydraulic conductivities and extensive aerial distribution, aquitards have been considered as candidates for waste storage and also for use as natural geotechnical liners and barriers at landfills [ Yanful et al , 1990; Rowe et al , 1993]. Consequently, a thorough understanding of the physical and geochemical processes that control and impact the transport of solutes in aquitard deposits is required to assess the suitability of these deposits to contain contaminants for time‐frames in excess of thousands of years.…”

Design and construction of the barrier system for the Halton Landfill

“…2) involves a 1.2 m thick compacted clayey till liner which is shaped to give a maximum liner thickness of 1.5 m at high points. The specifications for the liner, at the geotextile separator layers above and below the liner, were developed based on a detailed trial liner investigation (see Rowe et al 1993) which demonstrated the feasibility of constructing a 1.2 m thick recompacted liner (using unweathered upper till) over a stone layer (the simulated SLCL) and achieving a hydraulic conductivity of less than 3 × 10 -8 cm/s over more than 1 m of this thickness.…”

“…Quigley, personal communication). Based on the preliminary studies (Rowe et al 1993), the liner material was specified to have a minimum clay content of 20%, plasticity index of 7%, and a grain-size distribution with greater than 80% finer than 2 mm (i.e., passing No. 10 U.S. sieve).…”

“…These tests were conducted at a confining pressure of 100 kPa using Shelby tube samples (for justification see Rowe et al 1993 andRowe 2000). A total of 66 tests were conducted for cell 1 (6.5 tests/ha) and the data are summarized in Fig.…”

“…A detailed study of the feasibility of constructing this barrier system was conducted prior to landfill construction (see Rowe et al 1993). Construction of the landfill commenced in the summer of 1991.…”