## 4 Results and Discussion  
Influencing factors such as pore water resistivity, test temperature, sample saturation, and relative density have a significant impact on the resistivity of calcareous sand. The paper's study establishes a quantitative relationship between the resistivity of calcareous sand and the salt content and saturation of pore water through laboratory experiments. Effect of Temperature on the Electrical Resistivity of Single Size Fraction of Saturated Calcareous Sand  
The resistivity reflects the conductivity of calcareous sand and is closely related to the activity of ions in the solution. The change in temperature leads to a change in ion activity, which inevitably leads to a change in resistivity. To investigate the effect of temperature on the resistivity of saturated calcareous sand with different size fractions, an experiment was conducted to study the effect of temperature on resistivity. To prevent uneven temperature distribution in the sample caused by the heating device, which affected the resistivity test results, a constant temperature and humidity incubator was used to achieve temperature control of saturated calcareous sand samples, as shown in Figure 5. To prevent the evaporation of moisture from the sample, the sample was sealed after being placed in the sample box and then placed in the incubator. The temperature of the incubator was adjusted, and a constant temperature was maintained for at least 12 h.  
Saturated calcareous sand with relative density \(D_{\text{r}}\) = 0.6 and size fractions of 1-1.5 mm, 1.5-2 mm, and 2-2.5 mm were selected for electrical measurements. The current frequency \(f\) = 1000 Hz and saturation \(S_{\text{r}}\) = 100% were used to obtain the relationship curve between the resistivity of calcareous sand and temperature, as shown in Figure 6. Temperature had a significant impact on the resistivity of calcareous sand. As the temperature increased, the resistivity gradually decreased, and the conductivity of the sample increased. The possible reasons for this behavior included the following: (1) an increase in pore water temperature will reduce its viscosity and (2) as the temperature increased, the dissociation degree of pore water increased, and at the same time, the mineralization degree of pore water also increased, leading to a decrease in electrical resistivity [21]. Figure 5: Constant temperature and humidity incubator and test samples. The relationship between the resistivity and temperature of calcareous sand samples with different size fractions could be fitted using a logarithmic function. The fitting results are shown in Table 3, and all the fitting coefficients were greater than 0.95. For calcareous sands with size fractions of 1-1.5 mm, 1.5-2 mm, and 2-2.5 mm, for each 1 \({}^{\circ}\)C increase in temperature, the resistance decreased by 8 \(\Omega\), 15.683 \(\Omega\), and 19.088 \(\Omega\), respectively, while the resistivity decreased by 0.48 \(\Omega\cdot\)m, 0.94 \(\Omega\cdot\)m, and 1.15 \(\Omega\cdot\)m, respectively. A further explanation was that temperature significantly affected the conductivity of calcareous sand with larger particle sizes [22]. Therefore, when conducting research on different soil resistivities, it is necessary to pay attention to the influence of temperature. To prevent experimental errors caused by temperature, the solution and samples used in subsequent experiments were placed in a constant temperature and humidity curing box one day in advance, and the temperature was set at 20 \({}^{\circ}\)C.  
Effect of Pore Water Resistivity on the Electrical Resistivity of Single Size Fraction of Calcareous SandUsing the above six solutions, saturated calcareous sand samples with relative density \(D_{\text{r}}=0.6\) were prepared, consisting of three size fractions: 1-1.5 mm, 1.5-2 mm, and 2-2.5 mm. To prevent differences in ion adsorption by particles [16], calcareous sand was not reused.