# Research on the Accumulated Plastic Strain of Expansive Soil under Subway Loading
## 2 Dynamic Triaxial Test Plan
### Test Soil Samples and Remolded Soil Sample Preparation  
The test soil was extracted from the expansive soil samples located near the subway station of Xinqiao International Airport in Hefei City. The diameter of the soil samples was 80 mm and the height was 200 mm, as shown in Figure 2.  
The test soil was collected from the expansive soil at a subway station near Hefei Xinqiao International Airport in Hefei City. The soil samples were obtained with a diameter of 80 mm and a height of 200 mm. The retrieved soil samples of expansive soil were first subjected to a series of physical property index tests, with the experimental operations based on the \"Geotechnical Testing Methods Standard\" (GB/T50123-2019) [11]. The basic physical property indices of the undisturbed expansive soil samples are shown in Table 1, and according to the \"Technical Code for Construction of Expansive Soil Areas\" (GB 50112-2013) [12], the free swell ratio of the undisturbed soil samples falls within the range of 65% to 90%, therefore, the tested soil can be classified as moderately expansive.  
To ensure the uniformity of the soil texture and prevent the influence of physical parameter variations on the experiments, it was necessary to control other parameters and maintain consistency. Therefore, a series of studies was conducted using saturated remolded soil samples. The specific procedures for preparing the samples are as follows: (1) remove the soil sample from the sampling cylinder and cut it into slices, placing them on a tray. Then, put the tray into the drying oven and dry the soil at 110 \({}^{\circ}\)C for 24 h to ensure complete desiccation. (2) Crush and sieve the dried sample manually and mechanically, leaving soil particles with a diameter ranging from 1 mm to 2 mm. Then, thoroughly mix  
\begin{table}
\begin{tabular}{c c c c c c} \hline \(\omega\) & \(\rho\) (g-cm\({}^{-3}\)) & \(\mathbf{W}_{L}\) & \(\mathbf{W}_{P}\) & \(\mathbf{I}_{p}\) & \(\mathbf{\delta}_{ef}\) \\ (\%) & \(\rho\) (g-cm\({}^{-3}\)) & (\%) & (\%) & \(\mathbf{I}_{p}\) & (\%) \\ \hline
21.40 & 1.74 & 48.82 & 29.19 & 19.63 & 68 \\ \hline \end{tabular}
\end{table}
Table 1: Basic physical property indices of soil samples.  
Figure 1: Dynamic triaxial testing system (DYNTTS).  
Figure 2: Schematic diagram of continuous cyclic loading waveform in the dynamic triaxial test.  
the sieved soil and measure the moisture content of the sample. (3) Utilize the wet method for sample preparation. Calculate the mass and moisture content of the dry soil required for the experiment based on the predetermined moisture content and maximum dry density. Add water to the dry soil container to reach the required moisture content. Additionally, cover the surface of the container with a damp cloth and allow it to rest undisturbed for 12 h to ensure uniform moisture distribution within the soil material. (4) Following the completion of wet soil sample preparation, employ a compaction method to compact the soil sample. Weigh the designated sample quantity, then pour it into the compaction mold in seven layers, ensuring an even distribution and leveling the soil surface. Throughout the testing process, it is essential to maintain consistent layer heights, and the layered surfaces should undergo trimming to remove excess soil. (5) Once the compaction is finished, use a cutting ring to extract a soil sample for weighing. Measure the moisture content of the soil samples cut from both ends of the ring, with an acceptable error range of \(\pm 1\%\). After completing the sample preparation, wrap it with cling film and allow it to rest undisturbed in preparation for the dynamic triaxial test.