# Study on Frost Heave and Thaw Settlement Characteristics of Sanya Estuary Channel Soil Layer
## 3 Frost Heave and Thaw Settlement Experiment Content and Methods  
### Experimental Instruments for Frost Heave and Thaw Settlement  
The experimental instruments used in this study were provided by the Department of Underground Architecture and Engineering at Tongji University (Shanghai, China). The primary equipment includes a freezing apparatus, a low-temperature circulation pump, a data acquisition system, and a PC. The experimental system is shown in Figure 1.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Soil Layer** & **Soil Layer** & **Natural Density** & **Natural Moisture** & **Bulk Density** & **Permeability** \\  & **Number** & **(g/cm\({}^{3}\))** & **Content (\%)** & **(kN/m\({}^{3}\))** & **Coefficient (cm/s)** \\ \hline Fine sand layer & 4-1 & 2 & 17.5 & 0.0231 & \(2.70\times 10^{-3}\) \\ Silty clay layer & 1-2 & 1.84 & 30 & 0.0235 & \(7.99\times 10^{-6}\) \\ Gravel sand layer & 6-2 & 2.21 & 12.1 & 0.0243 & \(7.99\times 10^{-3}\) \\ Clay layer & 1-3 & 1.86 & 34.78 & 0.0246 & \(4.00\times 10^{-6}\) \\ \hline \end{tabular}
\end{table}
Table 1: Mechanical Parameters of Different Soil Layers.  
The specific experimental instruments include the following:  
1. Unidirectional Freezing Apparatus  
The sample size was selected based on the \"Code for Frozen Soil Testing\" (MT/T593.2-2011), considering the existing experimental conditions and objectives. Soil samples with a diameter of 12 cm and a height-to-diameter ratio of 0.5 were used for the tests. The size of the test chamber was 40 cm \(\times\) 40 cm \(\times\) 80 cm. The general structure of the freezing apparatus is shown in Figure 2.  
Figure 1: Schematic Diagram of the Experimental System.  
Figure 2: Schematic Diagram of the Freezing Apparatus.  
(2) Low-Temperature Cooling Liquid Circulation Pump  
The HRT-100 N low-temperature cooling circulation pump was used in the experiment. This device achieves the freezing effect by mechanically cooling and circulating the low-temperature liquid. In this experiment, silicone oil was used as the cooling medium, which was transported to the bottom of the freezing apparatus to provide continuous low temperatures to the bottom of the sample, achieving the freezing effect. The actual equipment is shown in Figure 3.  
(3) Temperature Sensors and Data Acquisition System  
The temperature sensors used in this study are T-type thermocouples (Figure 3(a)), with a temperature range of \(-200\)\({}^{\circ}\)C to \(260\)\({}^{\circ}\)C and an accuracy of 0.1 \({}^{\circ}\)C. The Keithley 2700-7700 temperature acquisition instrument was connected and Word software (Microsoft office 2021) was used to collect temperature data, as shown in Figure 3(b), to meet the test requirements. During the freeze-thaw tests, thermocouples were placed every 1 cm in the soil sample to measure the temperature changes during the freezing and thawing processes, allowing the study of the temperature field changes in the sample.  
Figure 4: Temperature Data Acquisition System.  
Figure 3: Refrigeration and Heating Circulator.  
(4) Displacement Sensors and Data Acquisition System  
The displacement sensors used in this study are DH-YWC-20 strain-type displacement sensors (Figure 5a), with measurement coefficients of 279, 286, and 295 \(\mu\epsilon/\)mm, and a displacement range of 0-20 mm. The displacement data acquisition instrument used was the TST3828E dynamic and static signal testing and analysis system (Figure 5b), with a resolution of 1 \(\mu\epsilon\) and a range of 0 to \(\pm\)19,999 \(\mu\epsilon\), meeting the experimental requirements.