## 5 Numerical Simulation of Monitoring Equipment in Cohesive Soil
### Analysis of Computational Results  
Based on the sensitivity parameters for linear heat sources in the numerical simulations, finite element models were established for iron-based linear heat sources and PVC-based linear heat sources in cohesive soils with different moisture contents: 5% (lower limit), 15% (lower limit), 15% (upper limit), 25% (lower limit), 35% (lower limit), 35% (upper limit), and 45% moisture  
Figure 8: The results for 15% (upper) water content cohesive soil: **(a)** ferrous heat source; **(b)** PVC heat source.  
Figure 7: The results for 15% (lower limit) water content cohesive soil: **(a)** ferrous heat source; **(b)** PVC heat source.  
Figure 9: The results for 25% (lower limit) water content cohesive soil: **(a)** ferrous heat source; **(b)** PVC heat source.  
Figure 11: The results for 35% (lower limit) water content cohesive soil: (**a**) ferrous heat source; (**b**) PVC heat source.  
Figure 12: The results for 35% (upper limit) water content cohesive soil: (**a**) ferrous heat source; (**b**) PVC heat source.  
Figure 10: The results for 25% (upper) water content cohesive soil: (**a**) ferrous heat source; (**b**) PVC heat source.  
From Figures 6-13, it can be observed that there are significant differences in the temperature distribution of iron- and PVC-based linear heat sources in both seawater and cohesive soil. There is a substantial temperature gradient at the interface between water and soil, and this gradient becomes more pronounced with time. This is because when a linear heat source is placed in the soil medium, the soil has a lower thermal diffusivity, resulting in a slower rate of heat transfer and a slower increase in temperature at the surface of the linear heat source. In contrast, when the linear heat source is in a water medium, the water has better thermal diffusivity, allowing heat to quickly transfer from the linear heat source to the surrounding environment. As a result, the surface temperature of the linear heat source is in a water medium, and the water medium is in a water medium.  
Figure 14: Iron heat source, temperature field distribution in 45% moisture content cohesive soil.  
Figure 13: The results for 45% moisture content cohesive soil: (**a**) ferrous heat source; (**b**) PVC heat source.  
Figure 15: PVC heat source, temperature field distribution in 45% moisture content cohesive soil.  
source increases more rapidly in water. Therefore, by monitoring the changes in the surface temperature of the heat source, one can analyze the variation in the temperature of the linear heat source in different media and determine the position of the water-soil interface in cohesive soil. Furthermore, there are significant differences in the temperature gradients at the water-soil interface between iron-based and PVC-based linear heat sources. The temperature gradient range of the iron-based linear heat source is larger, and it increases with time, while the PVC-based linear heat source has a smaller temperature gradient range, which increases over time.  
From Figures 14 and 15, it can be observed that both types of linear heat sources, made of different materials, cause the temperature and its propagation range in the soil to gradually increase over time. However, there are notable differences in the impact range of iron- and PVC-based linear heat sources on the soil at the same time. The temperature rise in the vicinity of the iron-based linear heat source is faster than that in the PVC-based linear heat source at the same time, indicating that the iron-based linear heat source has better thermal conductivity with cohesive soil. Nevertheless, the influence range of the temperature field in the soil for both types of linear heat sources is relatively similar.