Effect of Polyacrylamide on Improvement of Dredger Fill with Vacuum Preloading Method

Dredger fill possesses undesirable engineering properties due to high water content, compressibility, and low permeability, causing insufficient consolidation and long treatment periods using a vacuum preloading method. This paper investigates an advanced treatment method using chemically additive polyacrylamide (PAM) on dredger fill combined with a vacuum preloading method via laboratory model tests. Anionic polyacrylamide (APAM, a PAM class based on ionic classification) exhibited better performance on accelerating water discharge, reducing the time for trial filtration tests almost in half, and so was adopted in vacuum preloading model tests. The test results show that the application of APAM reduces 30% to 50% of the dredger fill consolidation time, accelerates the dissipation of excess pore pressure, and reduces the vacuum loss in vertical transition for the whole treatment duration. The vane shear strength post-treatment was observed to increase by 30% to 55% with an additive percentage of 30 mg/L of APAM, which is proposed for the treatment of Tianjin Binhai dredger fill. The results provide a novelty approach to the physical mechanical alteration of dredged fill to break through the unsatisfactory limitation of conventional vacuum preloading treatment.