# Study on Frost Heave and Thaw Settlement Characteristics of Sanya Estuary Channel Soil Layer
## 1 Introduction  
With the rapid economic development in China and the continuous advancement of urbanization, the demand for urban commuting is increasing, leading to a rise in the number of large underground structures. Currently, the pipe-roof method and artificial freezing method are two widely recognized methods in underground engineering, providing effective solutions for ground displacement and water seepage problems, respectively. Combining these two methods has led to the pipe-roof freezing method. However, pipe-roof freezing construction can cause frost heave and thaw settlement in the soil, which impacts the safety of the construction and the surrounding environment, and in severe cases, can lead to safety accidents, failing to meet the requirements for safe construction. Therefore, an in-depth investigation of the frost heave and thaw settlement characteristics of the soil during pipe-roof freezing construction has become crucial. Soil frost heave consists of in situ frost heave caused by phase change of water and segregated ice frost heave caused by moisture migration. This phenomenon has been confirmed in the soil freezing experiment results of [PERSON] [1] and [PERSON] [2], while [PERSON]'s first frost heave theory [3, 4] and [PERSON]'s second frost heave theory [5, 6] have provided important theoretical support for better understanding of the mechanism of soil frost heave. When the soil absorbs heat after forming frozen soil, the ice in the soil melts, causing the soil volume to decrease and resulting in thaw settlement. Subsequently, the melted soil undergoes drainage consolidation due to self-weight or external load, leadingto compaction settlement. The total settlement displacement of the soil resulting from the combined effects of these two settlements is called the thaw settlement of frozen soil [7; 8]. As theoretical research progresses, more scholars are conducting indoor experiments to further study the frost heave and thaw settlement phenomena of soil during freezing construction. [PERSON] et al. [9] investigated the frost heave and thaw settlement around piles in western China through indoor experiments, exploring the relationship between temperature, water content of unfrozen soil, and soil displacement around piles. [PERSON] et al. [10] studied the effects of initial soil moisture content and freezing temperature on soil frost heave characteristics, concluding that significant frost heave deformation occurs during the transitional freezing stage. [PERSON] et al. [11] discovered that the temperature gradient formed within the sample drives internal frost heave in the soil, where an increase in the temperature at the warm end raises both the water supply temperature and soil temperature nearby, thereby inhibiting the development of soil frost heave. [PERSON] et al. [12] established a multiple linear regression model using MATLAB to predict the influence of initial moisture content, clay content, compaction, and overburden load on the frost heave rate of clay-improved coarse-grained soil. [PERSON] et al. [13] investigated the moisture migration and frost heave characteristics of clay used as fill material under short-term, high-frequency, shallow freezing conditions. [PERSON] et al. [14] conducted indoor frost heave tests on saturated silty clay in Shanghai to study soil frost heave performance under different freezing temperatures. [PERSON] et al. [15; 16] used a self-made moisture migration test system to study the effects of initial moisture content, dry density, and freezing temperature on moisture migration during freeze-thaw cycles for both undisturbed and remolded soil samples. [PERSON] et al. [17] studied the relationships between frost heave rate, thaw settlement coefficient, fine particle content, initial moisture content, and the number of freeze-thaw cycles through freeze-thaw tests on highway subgrade soil.