Consolidation of Sludge Dewatered in Geotextile Tubes under Combined Fill and Vacuum Preloading

Recently, permeable geotextile tubes in conjunction with prefabricated horizontal drains (PHDs) have become increasingly popular for dewatering high water content slurries or sludge. However, how to analyze the consolidation process of the sludge in the geotextile tube so as to provide a proper design and prediction becomes a technical challenge. In this paper, we have proposed a two-dimensional plain-strain consolidation model for sludge consolidation in a geotextile tube under combined fill and vacuum preloading. A semi-analytical solution was obtained and validated through experimental observations. A salient finding of this study is the identification of a critical condition at which the optimum consolidation efficiency is achieved. Consolidation efficiency decreases gradually beyond this critical condition, which arrives later as the PHD pave rate and element height to width ratio increase. Furthermore, this analytical method clearly shows how preloading affects the dewatering process and the effect of fill surcharge is more pronounced than that of vacuum preloading of the same magnitude, owing to the vacuum attenuation and leakage.