Fully coupled large-strain consolidation and contaminant transport model for PVD-treated dredged sludge under vacuum-surcharge preloading

Abstract

Installing prefabricated vertical drains (PVDs) combined with vacuum-surcharge preloading promotes contaminant transport and leads to solute redistribution. This process is governed by complex interactions among soil deformation, water flow and solute transport. Simplified uncoupled analyses fail to properly reproduce such coupled responses, leaving the mechanisms of hydro-mechanical-chemical (HMC) coupling poorly elucidated. Therefore, a fully coupled HMC large-strain model is developed to evaluate consolidation and contaminant transport within dredged sludge treated with PVDs. The model is validated by comparing with existing models and field data. The results reveal that when the strain reaches 25.5%, the maximum discrepancy in consolidation predictions between large-strain and small-strain theories is 7.1%, with a 14% difference in final contaminant removal rate; for an initial contaminant concentration c 0 = 200 mg/L, neglect of full coupling leads to maximum deviations of 20.2% in excess pore water pressure (EPWP) and 34.4% in contaminant concentration; the time-dependent permeability decay of PVDs cannot be ignored, whereas depth-related permeability decay exerts an insignificant influence. The proposed model provides a theoretical basis for risk-based design and engineering management of reclamation projects using contaminated dredged sludge.