Centrifuge modeling of backfill consolidation in soil-bentonite cutoff walls

Soil-bentonite (SB) is commonly adopted for the backfill of vertical cutoff walls to contain contaminated groundwater. The permeability of SB backfill is dependent on its effective stress state, which is affected by the backfill consolidation process. This paper presents a geotechnical centrifuge model test to simulate the primary consolidation of typical SB cutoff walls with the advantages of reduced scale in time and size. The moisture content and earth pressure of the wall were monitored at varied depths. Test results showed that the rapid consolidation stage developed swiftly and various consolidation indicators exhibited significant development. Within the buried depth over the half (approximately two-thirds), the distribution of vertical effective stress was similar to the Bucknell field testing results, namely that it increased nonlinearly and then tended to stabilize. Also, the cumulative effect of lateral frictional resistance increased with depth and reached its peak value. In the deeper buried areas, lateral frictional resistance decreased sharply before increasing again with increasing depth, while vertical effective stress followed a pattern of significant increase followed by a decrease, which was found to be in good agreement with the predicted model compared in the literature. Analysis of consolidation behaviour and mechanisms could be fully validated from directly monitored indicators, including excess pore pressure dissipation, consolidation settlement, moisture content distribution patterns, and permeability coefficient inside the wall. This centrifuge test may be useful for achieving a comprehensive evaluation of the consolidation behaviour and mechanism of SB cutoff walls.