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 × 10−8 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. Key words : waste disposal, clay liners, geotextiles, field performance, hydraulic conductivity, landfills.