*2.1. Slurry*

In order to study the flocculation–sedimentation and solidification characteristics of waste pipe jacking slurry, waste slurry from a pipe jacking project in Zhenjiang, Jiangsu Province, China, was used as the test material. The sampling of the waste slurry at the site was carried out twice. The first sampling time was on 4 January 2021 (Type I slurry), and the second was on 26 March 2021 (Type II slurry). According to the construction report of the pipe jacking project, the construction was excavated to a special stratum in March 2021. To maintain the stability of the excavation surface, more bentonite was added to the slurry. Therefore, Type II waste slurry was mixed with some bentonite. Table 1 shows the basic properties of the pipe jacking waste slurry. Particle size distribution of the slurry was measured by a laser particle size analyzer, the Malvern Mastersizer 2000. The slurry was diluted to a water content of 300%. The sample was dropped into the Hydro MU dispersion unit through an eyedropper, and was dispersed by ultrasound and stirring. The obscuration parameter was kept between 10% and 20% to ensure good quality of the signal. The pump speed was set as 2000 r/min. The particle size distribution of waste pipe jacking slurry can be seen in Figure 1. Type II slurry has a smaller particle size because it contains bentonite, with an average particle size of 7.84 μm, while the average particle size of Type I slurry is 15.78 μm.


**Table 1.** Basic properties of the pipe jacking slurry.

**Figure 1.** Particle size distribution of the pipe jacking waste slurry.

## *2.2. Conditioners*

Four types of commercial polyacrylamide (PAM) were used for flocculation, manufactured by Shanghai Wshine Chemical Co., Ltd., Shanghai, China. Four types of PAM were recommended by the manufacturer because of their good effect in the reduction of tailings slurry. Wshinefloc 412VS and 611HN are cationic polyacrylamide (CPAM). Wshinefloc 7126 and 720VJ are anionic polyacrylamide (APAM). The specific parameters of PAM are shown in Table 2. The flocculant was reconstituted every day, at a concentration of 0.1% (*w*/*w*).

**Table 2.** Chemical properties of PAM used in this study.


Ferric chloride (FeCl3·6H2O) was used as a coagulant in composite conditioning, which is produced by Shanghai Yuanye Biological Co., Ltd., Shanghai, China, and its molecular weight is 270.3 g/mol.

#### *2.3. Solidification Agent*

The 425# ordinary Portland cement (OPC) and sulphate aluminum cement (SAC) were selected as the solidification agent. SAC has a faster hydration rate than OPC, which can make the solidified soil achieve a higher strength at a shorter curing age. SAC was used to test whether it can make the sediment reach the required strength earlier in solidification experiments.
