Abstract: The line heat source method of soil moisture monitoring requires higher heating power. When the intensity of the heat source is unstable, the monitoring results are easily affected. To solve the shortcomings of the line heat source method, a mobile point heat source (PHS) method for soil moisture monitoring is developed in this study. This method uses the correlation between the thermal physical properties of soil and the moisture content to indirectly identify the moisture content by monitoring the cooling law of the PHS in the soil. Firstly, the heat transfer law of the PHS in the soil with evenly distributed moisture content was examined through numerical simulation. According to the characteristics of the cooling curves of the heat source, the moisture content discrimination index η was defined, and then the fitting relationship between the moisture content and the discrimination index was established. In addition, parameter analysis was carried out on the factors affecting the monitoring sensitivity. Then, numerical simulation of the PHS cooling law was carried out in the soil with unevenly distributed moisture content, and the moisture content discrimination index was calculated according to the time history curve at the cooling stage of the measuring point. After that, the moisture content distribution was inverted by the fitting formula of the moisture content and the discrimination index. The results show that the moisture content distribution inverted by the PHS method is in good agreement with the actual value, which verifies the theoretical feasibility of the method. Finally, the feasibility of the method is further verified by model tests.

Key words: soil moisture')">

soil moisture, point heat source, fiber Bragg grating, cooling law, numerical simulation