Laboratory experiments on HMC coupling mechanisms in innovative clean foundation treatments for Zn-contaminated dredger fills

Abstract

Large-scale contaminated dredger fills have comprehensively resulted from human activities and geological deposition processes, and their disposal is a worldwide challenge. Innovative soil remediation coupling foundation treatment methods, namely, clean foundation treatment methods (CFTMs), were proposed and verified using a hydraulic–mechanical–chemical coupling triaxial testing system. The CFTM exploration triaxial tests on undisturbed clayey, silty, and sandy dredger fills showed that the critical injection significantly dilated soil volume even after the soil was vacuum pumped. Critical injection–vacuum soil flushing (CIVF), critical injection soil flushing (CIF), and vacuum soil flushing (VF) were proposed to perform clean foundation treatment for clayey silt, sandy silt, and silty sand of 1900–2300 ppm Zn. EDDS, HCl + CaCl2, and HCl were selected as the three chelating agents. Orthogonal tests on three factors (CFTM, soil type, and eluent) showed that CIF with 5:1 EDDS aq. of pH 3.8 was the best CFTM scheme for the three soil types at a depth of 2.5–10 m. CIF with HCl aq. of pH 3.8 also reached a high comprehensive clean foundation treatment efficiency for silty sand at a depth of 2.5 m. The deep depth and heterogeneous texture resulted in low Zn contamination extraction efficiency.