Critical air entry value-controlled vacuum consolidation of clayey sludge with horizontal drains

The prefabricated horizontal drain (PHD) is increasingly being used for the treatment of high water content slurries with vacuum preloading, thanks to its higher efficiency as compared to the conventional prefabricated vertical drain. However, certain issues concerning the air–liquid interface of PHD systems, e.g., improved geotextile tubes or slurry pits, require further investigation. In fact, air entry-induced vacuum failure can occur when the surface suction exceeds the critical air entry value (CAEV, corresponding to the intersection point of the compression curve and the void ratio–AEV curve). Existing models, which assume that the excess pore-water pressure remains zero at the drainage boundary, may significantly underestimate the soil consolidation. In this study, a CAEV-controlled large-strain consolidation model is proposed to simulate the dewatering process of vacuum-preloaded clayey sludge, incorporating the geometrical and mechanical nonlinearities and self-weight of soil. Numerical solutions are obtained using the alternative direction implicit algorithm and are validated through laboratory and field model tests. Further analysis indicates that the discrepancy between the proposed model and the traditional model increases with the increasing horizontal spacing of PHDs, decreasing thickness of the geotextile tube or soil layer, and increasing CAEV.