Experimental investigation on prefabricated horizontal drain-based vacuum dewatering-solidification combined method for treatment of dredged slurry

The dredged slurry exhibits the characteristics of high water content, low permeability, high compressibility and low or negligible bearing capacity, and is difficult to be rapidly treated and disposed of. Aiming at this problem, a composite method, i.e., the combined method of prefabricated horizontal drain-based vacuum dewatering and solidification, abbreviated as PHDVDS, is introduced, and a series of model tests are carried out to investigate the volume reduction and reinforcement effects of the PHDVDS method, with lime-activated ground blast furnace slag (GGBS) and cement as the binder, respectively. The performance of PHDVDS method is compared with that of the pure vacuum dewatering method (no binder) and the pure solidification method (no vacuum dewatering, using cement as the binder). During the vacuum dewatering stage of the model tests, the mass of discharged water and the settlement, i.e., volume reduction, are monitored, after which the unconfined compressive strength (UCS) of soil samples at different curing ages is tested, and the development of UCS is analyzed from microstructural point of view by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results indicate that, compared with the pure vacuum dewatering method and pure solidification method, the PHDVDS method demonstrates significantly better volume reduction efficacy and significantly better reinforcement efficacy. For instance, the volume reduction by the PHDVDS method after two-day vacuum dewatering is 7%~43%, higher than that by the pure vacuum dewatering method. The 60-day UCS of the PHDVDS-treated soil is 6 times~54 times higher than that of the pure solidification method.