## 3 Results  
### Analysis of Water Displacement, Moisture Content, Shear Strength  
Figure 4 shows the change curve of volume of drained water with time. The final volumes of drained water of the tests in groups T1-T6 are 1087.01 mL, 1295.10 mL, 2292.38 mL,  
836.26 mL, 1229.76 mL, and 2014.66 mL, respectively. Comparison of T1-T3 or T4-T6 group tests shows that: electro-osmosis drainage < vacuum < vacuum electro-osmosis, and vacuum electro-osmosis significantly increases the final drainage compared to single electro-osmosis and single vacuum. In addition, it can be seen from the figure that the growth of the discharge volume goes through a rapid and then slow phase. From T1 and T4, it can be seen that the drainage growth of the electro-osmosis method is more stable, and the drainage rate only slightly decreases until about 24 h. From T2 and T4, it can be seen that the vacuum method can be divided into two stages, first rapid drainage until about 12 h, the drainage growth continues to slow down to almost no more growth. From T3 and T6, it can be seen that the vacuum electro-osmosis method can likewise be divided into two stages, with rapid drainage up to about 8h in the early stage, when the drainage rate is the fastest, followed by a slow attenuation to nearly parallel to the growth of electro-osmosis drainage, i.e., at essentially the same rate. Consequently, it can be stated that the effect of vacuum is mainly reflected in the early stage of rapid drainage, while the later stage of drainage is mainly controlled by electro-osmosis. It is mainly due to the fact that--in the early stage--when the blockages inside the soil and near the drainage board are not severe, the water is discharged faster under the action of the vacuum. After the later blockage occurs, the degree of soil compaction increases, and the drainage effect decreases rapidly. The effect of electro-osmosis is less affected by it; hence, vacuum electro-osmosis can combine the advantages of both to achieve the best treatment effect. As can be seen in the figure, the trend of drainage volume in the presence or absence of contaminants is basically the same for any one engineering method, indicating that the presence or absence of contaminants in the soil does not affect the above law. However, it can be seen from the graph that the final discharge: T1 < T4, T2 < T5, T3 < T6. It suggests that the discharge of either engineering method in the case with pollution is smaller than its counterpart in the case without pollution. It indicates that the presence of contaminants reduces the final drainage volume and the impacts of the contaminant metals on the electro-osmosis method are more significant than that on the vacuum method. At the end of each group test, three points are taken evenly along the vertical direction of the anode, middle, and cathode positions to measure the moisture content and vane shear strength, as shown in Figure 3. The average value of the corresponding three points is the moisture content and shear strength at that location. Figures 5 and 6 show the  
Figure 4: Change curve of the volume of drained water with time. distribution law of the moisture content and shear strength of the soil, respectively. The moisture content was 75% before the test, and after treatment, the moisture content at the anode ranged from 40.6% to 52.5%, the moisture content at the middle position ranged from 48.1% to 66.6%, and the moisture content at the cathode position ranged from 43.1% to 60.6%. It can be observed that regardless of the soil contamination, both sides have a lower moisture content and the middle position has a higher moisture content. As the water at the anode is moving to the cathode, the cathode drains on one side and the moisture content is low on both sides, and the water is mostly gathered in the middle position and the moisture content is high in the middle. As can be seen in Figure 5, the moisture content of the contaminated soil is greater than that of the pollution-free soil, which is consistent with the law of drainage.