## 2 Experimental Methods
### Experimental Procedures  
#### 2.3.1 Triaxial Test  
1. Sample Preparation  
A solid cylinder with a diameter of 50 mm and a height of 100 mm was prepared for this test. The compaction method was chosen in accordance with the Specification of Soil Test (GB/T50123-2019). Soil samples were divided into five parts. Each component was poured layer by layer into the sample preparation device and then pressed to the specified height according to the designed water content and density. The upper plane of the previous layer was scraped away, and the next layer of soil was added and compacted to ensure the uniformity of the soil samples.  
2. Saturation  
The soil sample was loaded into the vacuum pumping cylinder and then saturated using the vacuum saturation technique. The vacuum cylinder was connected to the air extraction pump to maintain negative pressure of 100 kPa for one hour, and airless water was then slowly injected from the bottom of the soil sample. After the sample had been completely submerged in water, drainage was stopped, and air extraction continued for another half an hour. Valves were then completely closed to keep the sample submerged in water.  
3. Consolidation  
Isotropic consolidation was used in the test. After loading the soil sample, the pressure chamber was installed. Then the sample was contacted and zeroed axially, and the confining pressure was added to the specified value. Consolidation began once the pore water pressure had reached a stable level, and the check saturation had met the specified requirements. Consolidation was completed when the pore water pressure of the sample had dropped by more than 95%.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Number** & **Stress Paths (kPa)** \\ \hline Conventional CU triaxial test & A\(-\)0 & 150 \\ \hline \multirow{2}{*}{CU triaxial tests under lateral unloading} & B\(-\)1 & 150\(\rightarrow\)140\(\rightarrow\)130\(\rightarrow\)120\(\rightarrow\)110\(\rightarrow\)100\(\rightarrow\)90\(\rightarrow\)80\(\rightarrow\)70\(\rightarrow\)60 \\  & B\(-\)2 & 150\(\rightarrow\)130\(\rightarrow\)110\(\rightarrow\)90\(\rightarrow\)70\(\rightarrow\)60 \\ \multirow{2}{*}{stress paths} & B\(-\)3 & 150\(\rightarrow\)120\(\rightarrow\)90\(\rightarrow\)60 \\ \hline \multirow{2}{*}{CU triaxial tests under lateral unloading–reloading stress paths} & C\(-\)1 & 150\(\rightarrow\)140\(\rightarrow\)130\(\rightarrow\)120\(\rightarrow\)110\(\rightarrow\)100\(\rightarrow\)90\(\rightarrow\)80\(\rightarrow\)70\(\rightarrow\)60\(\rightarrow\)150 \\  & C\(-\)2 & 150\(\rightarrow\)130\(\rightarrow\)110\(\rightarrow\)90\(\rightarrow\)70\(\rightarrow\)60\(\rightarrow\)150 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test scheme.  
4. Unloading and reloading  
After initial consolidation, the lateral stress of the sample was unloaded in stages in accordance with the test scheme. The sample was consolidated and then unloaded onto the next stage following each stage of unloading. Following unloading, the reloading process was also incrementally loaded until the target value had been reached. All loading and unloading rates were set at 1 kPa/min.
5. Three-dimensional shear test  
Consolidated undrained shear tests were performed on soil samples. In order to properly compare the mechanical properties of the three soils and reduce the test error, shear rate was set at 0.5%/min for silt, silty sand, and mucky silty clay. We monitored and recorded axial pressure, confining pressure, axial strain, and pore pressure until the axial strain had reached 15%.