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...
Considerations related to the design of the Halton Landfill as a "hydraulic trap" are summarized together with the research that was conducted to support the design concept. The interrelationship between hydrogeology and the engineered design is examined. Laboratory experiments demonstrated that there can be diffusion away from a source, even with significant inward velocity. Existing theory was found to provide a good prediction of the observed concentration profile in these experiments. It is also shown that a pressurized air pocket below the clay effectively acts as a zero-flux boundary and hence, with respect to migration of chloride, could be conservatively neglected in the impact assessment. The results of the impact calculations predict only a small increase in chloride concentration in the receptor aquifer while there is negligible predicted impact due to organic contaminants. The landfill was designed and constructed with a granular "sub-liner contingency layer" (SLCL) beneath the compacted liner. The operation of this layer is discussed. Finally, the construction of the compacted clayey liner with a hydraulic conductivity of 1 × 10-8 cm/s is documented.Key words: landfill, hydraulic containment, liner, field case, construction.
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