AN EVALUATION OF SOIL-BENTONITE BACKFILL CONSOLIDATION PROPERTIES-Paper

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The study examined how soil gradation and bentonite content affect the consolidation and hydraulic conductivity of soil-bentonite (SB) slurry-wall backfill. Laboratory tests used three base soils with fines contents of 6%, 42%, and 77%, mixed with 0–5% dry bentonite. Consolidometers measured hydraulic conductivity, compressibility, and consolidation rates under varying effective stresses.<br /><br />Hydraulic conductivity decreased substantially as effective stress increased, across all soil types and bentonite contents. Earlier results discussed in the paper also showed that higher fines and bentonite contents generally reduce hydraulic conductivity. Increasing either fines or bentonite content increased backfill compressibility.<br /><br />The coefficient of consolidation varied by nearly three orders of magnitude among mixtures and stress levels. Consequently, estimated times to 50% consolidation ranged from less than a day to 83 days; times to 90% ranged from a few days to 358 days. Higher fines and bentonite contents generally slowed consolidation.<br /><br />Analyses of expected wall stresses indicated that stresses are governed primarily by active earth pressures in the adjacent ground. Backfill stiffness had little influence on stress development over most of the conditions studied, though it affected the depth at which active pressure became controlling.<br /><br />Overall, backfill composition strongly affects consolidation time, while its compressibility has comparatively little effect on stress development. These findings highlight the need to consider both stress-dependent hydraulic conductivity and potentially prolonged consolidation when designing SB cutoff walls.

Keywords

soil-bentonite

slurry wall

hydraulic conductivity

soil gradation

bentonite content

consolidation

compressibility

coefficient of consolidation

effective stress

cutoff walls