# Compression Law and Settlement Calculation Method of Over-Wet Soil Based on Large Samples
## 2 Materials and Methods  
The soil samples were obtained from Hefei, Anhui Province, East China, which has a subtropical humid climate with an average annual precipitation of 900-1000 mm. The soil sample was approximately 0.5 m below ground level and was brownish-yellow, ranging from plastic to soft plastic. The sampling locations are shown in Figure 1. Figure 2 shows the sampling site. The water content, liquid limit, and plastic limit of the soil samples were measured in accordance with the guidelines given by ASTM [15]. The compaction curve of the sample is shown in Figure 3, with a maximum dry density of 1.765 g/cm\({}^{3}\) and an optimal moisture content of 12.62%. The humidity of each group of samples was calculated using Equation (2), and the results are presented in Table 1. Soil samples with a humidity of less than 100% were considered over-wet soil. The liquid limit exceeded 50%, which indicates a high-liquid-limit soil. The particle screening results are listed in Table 2, with approximately 80% of the particles being less than 0.075 mm; therefore, the soil is classified as clay. Figure 1: Sampling location. Figure 3: Compaction curve. Figure 2: Sampling site for over-wet soil. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Water Content** & **Liquid Limit** & **Plastic Limit** & **Plasticity Index** & **Optimum Water** & **Maximum Dry** & **Humidity** \\ _w/\%_ & _w\({}_{L}\)_/\%_ & _w\({}_{P}\)/\%_ & _I\({}_{P}\)/\%_ & **Content/\%_ & **Density/g-cm\({}^{-3}\)** & **(\%)** \\ \hline
16.80 & 58.0 & 24.2 & 33.8 & 13.3 & 1.765 & 92 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Natural water content as well as liquid and plastic limits of soil samples. Compacting over-wet soil is challenging owing to the high water content and difficulty in draining water. The phenomenon of \"springing\" may occur during compaction, where the compressed area sinks in, and the surrounding area springs back. Conventional one-way compression tests or triaxial tests have small sample sizes (\(\varphi\) = 61.8 mm, \(h\) = 20 mm, and \(\varphi\) = 50 mm, \(h\) = 100 mm) and short drainage paths, which cannot reflect the true conditions of over-wet soils in the stratum. In this study, a large-scale compression test apparatus was used. Figure 4 shows a schematic of the loading device. The sample size is \(\varphi\) = 200 mm, and \(h\) = 320 mm, with filter paper and permeable stone placed on the top and bottom of the sample, and with Vaseline applied on the inner wall. The lever loading method was employed, and electronic dial indicators and data collectors (SYNTEK, Hangzhou, China) were used to collect the deformation data continuously. The loading device was fixed to a steel frame, enabling the performance of multiple simultaneous sets of tests. Figure 5 shows the loading process. Using the water content and compaction as control parameters, samples were prepared with target water contents of 8%, 13%, 18%, 21%, and 26%. To prepare the samples, the soil was divided into three layers and placed in a sample cylinder. After leveling, the samples were compacted. The actual parameters measured after sample preparation are listed in \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Gradation/\%** & & & & & \\ \hline
**5 mm-20 mm** & **2 mm–5 mm** & **0.25 mm–2 mm** & **0.075 mm–0.25 mm** & **\textless{}0.075 mm** & **Classification** \\ \hline
0 & 0.17 & 1.88 & 1.03 & 96.92 & High liquid limit \\  & & & & clay \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Particle size distribution. Figure 4: Schematic of loading. Figure 5: Large compression instrument. To analyze the changes in free and bound water during the compression process of over-wet soil, a thermogravimetric (TG) analysis was conducted on sample 5 before loading and after different compression stages of 200 kPa (below the pre-consolidation pressure) and 400 kPa (above the pre-consolidation pressure). Figure 6 shows the ZRT thermogravimetric analysis system (Beijing Jingyi Hi-Tech Technology Co., Ltd., Beijing, China).