# Study on Frost Heave and Thaw Settlement Characteristics of Sanya Estuary Channel Soil Layer
## 4 Test Results and Analysis  
Analysis of Frost Heaving and Thawing Properties of Different Soil Layers under Natural Moisture Content  
The displacement of the top of the silty clay, clay, fine sand, and gravel sand during the freezing and thawing stages varies with time, as shown in Figure 6.  
By observing and analyzing, the soil sample displacement can be divided into frost heaving displacement and thawing displacement. The dotted line is the dividing line between the frost heaving displacement stage and the thawing displacement stage. The variation of frost heaving displacement can be roughly divided into four stages as follows:  
Stage One: Frost Contraction Stage. During this stage, the volume increase generated by the freezing of water into ice in the soil is not sufficient to offset the volume decrease caused by the low temperature, resulting in a decrease in the volume of the soil sample, leading to negative displacement. When the frost heaving amount exceeds the volume contraction of the soil, displacement starts to increase, marking the end of this stage.  
Figure 6: \(Cont.\)  
Stage Two: Rapid Frost Heaving Stage. During this stage, water particles near the freezing front in the soil sample quickly freeze into ice and form ice lenses, with a significant ice segregation phenomenon. Therefore, the frost heaving phenomenon in the soil sample is very strong, and the displacement growth rate is fast.  
Stage Three: Slow Frost Heaving Stage. During this stage, the ice segregation in the soil sample is fully developed, and the thickness and continuity of the ice lenses slowly increase, resulting in a slow increase in frost heaving displacement.  
Stage Four: Frost Heaving Stabilization Stage. During this stage, the freezing front is stable, the ice lenses no longer grow, and the frost heaving displacement slowly increases towards stabilization.  
The variation of thawing displacement can be divided into three stages as follows:  
Stage One: Slow Thawing Stage. Affected by the freezing temperature, the soil sample does not immediately show thawing displacement after the cold source is removed, resulting in a slow change in thawing displacement.  
Stage Two: Rapid Thawing Stage. During this stage, the thawing phenomenon in the soil sample is significant, and the thawing amount continuously increases with time, resulting in a fast change in thawing displacement.  
Stage Three: Thawing Stabilization Stage. During this stage, the change in thawing displacement of the soil sample is smooth, eventually stabilizing.  
Figure 6: Displacement Variation Curves of Different Soil Layers.  
By comparing and analyzing the displacement variation curves of the four soil samples, it can be observed that:  
1. The time required for the two types of sand to reach the stable displacement stage during freezing and thawing was shorter than that of the two types of clay, indicating that the thermal conductivity of the two types of sand was significantly greater than that of the two types of clay.
2. Due to the differences in soil properties, the coarse particles of the two types of sand led to lower moisture content during freezing and a less compressible sand skeleton during thawing, resulting in less pronounced frost heaving and thawing characteristics compared to clay.
3. After the test, all soil samples except gravel sand showed negative displacement, indicating that the frost heaving displacement of all soil samples except gravel sand was greater than their thawing displacement.  
The frost heaving rate and thawing coefficient of fine sand, silty clay, gravel sand, and clay were calculated, with the results shown in Table 2.  
Comparative analysis shows that the frost heaving rate and thawing coefficient of silty clay in the Sanya Estuary Channel Project were the highest. Based on the principle of the most adverse conditions, silty clay was selected for the analysis of frost heaving and thawing properties under different moisture contents in the next section.