Prefabricated horizontal drains (PHD) exhibit lots of priority against vertical drains in treatment of high moisture slurry. However, recent research reported a significant dewatering rate saltation (DRS) problem in PHD-treated slurry, and theoretical explanation and quantitative analysis are lacking. This research first reanalyzed the recently reported tests of PHD-and flocculant-treated slurry, where the DRS problem was studied through water discharge rate and soil-water height difference (Δh). Then, a 1D consolidation solution was proposed considering vacuum boundary and critical flow gradient. Relationship between consolidation time and height of the forward flow line was established to predict the vacuum transmission in the model test. In addition, the proposed method was used to back-analyze the time when the DRS occurs. Last, with assumed critical gradient and consolidation coefficient considering the flocculation effect, the DRS problem was theoretically investigated for different cases and the predicted results are reasonable compared with the test data.

No abstract

This study proposes a new method using the combination of flocculation and prefabricated horizontal drain (PHD) assisted with vacuum pressure for rapid dewatering of high-water-content dredged slurry. First, to demonstrate the superiority of using PHD over the more commonly used prefabricated vertical drain (PVD), experiments were conducted to compare the dewatering performance between the PHD and the PVD. Then six model tests with the proposed dewatering method were performed with various contents of flocculant (anionic polyacrylamide (APAM)) to investigate the effect of APAM content on the dewatering process and soil properties (i.e. undrained shear strength, permeability and compressibility). Furthermore, particle size distributions of the slurry before and after model tests were measured to analyze the dewatering behavior and changes in material properties. Finally, particle loss during vacuum consolidation for various APAM contents were compared to study the flocculation effect on clogging problem. Results indicate that the proposed method can prevent significant bending deformation of the drain board and mitigate clogging of the drain filter and, thus, can significantly accelerate the dewatering process of high-water-content dredged slurry.