## 1 Introduction  
In recent years, the treatment of black and odorous water has been a difficult issue in the field of civil engineering and environmental protection. Sediment dredging, as a common method, generates a large amount of contaminated dredged sediment during the treatment process [1; 2]. This type of sediment is mainly composed of fine-grained silty clay, which is difficult to dehydrate [3]. Moreover, it contains contaminant metals, among which Cu is one of the main contaminants in dredged sediment from lakes and rivers [4; 5]. Direct landfill or secondary use of this kind of dredged sediment can pose a risk to the surrounding environment and human health [6]. Thus, the treatment of contaminated dredged sediment should include dehydration to achieve reduction and heavy metal removal to achieve remediation. For the reduction of contaminated dredged sediment, some scholars have introduced vacuum preloading in the field of foundation treatment into sediment treatment. The advantage of this method is the simple construction technology and low cost [7; 8; 9]. However, as a traditional mechanical dehydration method, the vacuum preloading method has a long construction period, and the treatment effect is difficult to meet the requirements [10]. Additionally, the electro-osmosis method can be used to reduce the volume of dredged sediment, and has a better edge in dealing with this kind of fine-grained clay. By means of applying an electric field to the soil, water is transferred from the anode to the cathode under the function of electro-osmosis [11]. However, studies have demonstrated that electro-osmosis is limited by contact resistance, electrode corrosion, cracks, and other issues [12; 13]. Therefore, some workers have combined vacuum and electro-osmosis, taking into account the benefits of both dehydration and reduction treatment, and obtained relatively positive achievements [14; 15; 16]. However, the presence of contaminant metals will inevitably change the microscopic properties of the sediment, and there is still a lack of investigation into the dehydration reduction characteristics of contaminated dredged sediment. It is essential to evaluate the effect of the presence of contaminants on dehydration reduction and to clarify its influence mechanism. The remediation of the contaminated dredged sediment can also be accomplished with an external electric field. Electrokinetic remediation displays better behaviors in terms of metal mobilization and low repeated pollution [17]. Under the operation of the external electric field, heavy metal ions, are pooled under the simultaneous function of electro-osmosis, electro-migration, diffusion, and other mechanisms [18; 19; 20]. The interactions between multiple driving forces are complex and still need further clarification. Most of the single electrokinetic remediation experiments are based on the anode and cathode electrolytic cells to achieve the gathering of contaminants, which are inconvenient to discharge directly [21; 22; 23]. The intervention of the vacuum preloading method has made it a possibility to simultaneously pool and discharge heavy metal. Nevertheless, as dehydration proceeds, the impact of the stress field change on contaminant migration after consolidation and deformation of the sediment remains to be identified. The influence characteristics of dehydration reduction on the pollutant removal mechanism need to be evaluated and the pollutant removal should be analyzed. The influence of dehydration on the removal mechanism of contaminant metals needs to be estimated and the contaminant removal should be also analyzed. The current studies are mostly conducted in a single reduction or remediation condition. For the simultaneous operation conditions, on the one hand, there are common influencing factors, such as potential, current, and cracks between the two, but there are differences in the degree of influence [24].