Compressional rheology model for vacuum filtration-consolidation of sludge in geotextile tubes

Recently, the disposal of high-water-content dredged sludge through geotextile tubes with vacuum-assisted prefabricated horizontal drains (PHD) has gained growing popularity for its convenience and efficiency. However, existing simulations for this typical coupled filtration-consolidation process using conventional consolidation models exhibit deficiencies due to the absence of effective stress and invalidity of Darcy’s law in the particle-wandering filtration phase. In this study, based on the compressional rheology theory, a two-dimensional coupled filtration-consolidation model constituted by the compressive yield stress Py(ϕ) and hindered setting factor r(ϕ) is developed to elucidate the solid-solid and solid-fluid interactions during slurry dewatering. A novel approach for measuring consistent Py(ϕ) and r(ϕ) relationships is proposed. The numerical solution is derived utilizing the alternating direction implicit (ADI) difference method and verified against a classical one-dimensional compressional rheology model and a field trial. Further analysis suggests that constitutive parameters, e.g., gel point, affect the dewatering efficiency by determining the relative degree of soil disorder, obstruction to particle movement, and vacuum transmission effect, while design parameters, e.g., PHD spacing and tube height, impact the magnitude and radiation range of vacuum pressure to influence the overall efficiency.