Rapid treatment of high-water-content dredged slurry using composite flocculant and PHD-facilitated vacuum

Flocculation by chemicals can adequately reduce the clogging effect, and the bending effect of prefabricated vertical drains can be eliminated by laying a prefabricated drain in the horizontal direction. Various settling column tests with different contents of chemicals, polyacrylamide (PAM) and hydrated lime (Ca(OH)2), were initially conducted to find the optimum dose for the fastest settling. Then, the combined effect of using both PAM and lime on the dewatering behavior of dredged clay slurry is studied using a prefabricated horizontal drain (PHD) and vacuum pressure of 80 kPa. Initially, sedimentation and self-weight consolidation with the optimum dose of PAM and lime are allowed to occur, and then further vacuum preloading is carried out. The combined effect of lime and PAM is very effective in increasing the dewatering rate, taking only 207 hours in comparison to 247 hours for the soil slurry treated with only PAM and 411 hours for the soil slurry without any chemicals. After the treatment, the shear strength substantially increases to 58.5 kPa for the soil with lime and PAM in comparison to 42.8 kPa for the soil with PAM only and 16 kPa for the soil without any chemicals.