## 4 Analysis of Seepage Locating  
It can be seen from the above analysis that the distribution of the seepage field can be inversed by the temperature field measured using the optical fiber, but the seepage field is steady at this time. In order to obtain the real-time change in seepage field using the optical fiber, the study of optical fiber seepage measurement and positioning is carried out. Figure 11: Temperature distribution in medium II with a seepage velocity of 0.6 \(\times\) 10\({}^{-3}\) m/s. Figure 12: Different distributions in different media. Figure 10: Temperature distribution in medium I with a seepage velocity of 0.6 \(\times\) 10\({}^{-3}\) m/s. The seepage locating technology using the optical fiber relies on the fact that the optical fiber can sensitively sense the temperature change in the surrounding medium. For the pre-heated optical fiber, the temperature distribution is constant and stable. When seepage flow exists, the temperature of the optical fiber decreases due to thermal convection. However, for the optical fiber part without the influence of seepage, the temperature will not change. Therefore, this paper discusses the optical fiber temperature measurements and seepage measurements in various states, mainly including the seepage in unsaturated state, the seepage in saturated state, and the seepage in saturated-unsaturated state. For the seepage analysis of unsaturated soil shown in Figure 13, which represents the temperature rise in the optical fiber under the natural state condition, the temperature rise can be observed by changing the heating power of the optical fiber. The chosen heating power of the optical fiber is 6 W/m, 12 W/m, and 18 W/m, respectively. As the heating temperature of optical fiber increases, under the action of the seepage water, the temperature of the optical fiber decreases due to heat convection and heat exchange. The test mainly analyzes the accuracy and location of optical fiber seepage measurement through the pre-buried centralized leakage channel. The test shows that the optical fiber seepage measurement and positioning method can obtain good results for three different design conditions. It can be noticed in Figure 14 that the temperature at the 14.2 m, 17.3 m, and 23.3 m positions in unsaturated soil is lower than that of the surrounding area, which means that those positions can be determined to be the concentrated seepage channels. Then, the averaged accuracy of seepage location is 1.3%. In Figure 15, for the seepage area, the temperature drop in the fiber is immediately affected by the seepage water, and the temperature drop period lasts for about 220s before temperature becomes stable. Combined with the coupling theory of the temperature field and seepage field in the third section, in the practical engineering application process, the internal temperature-seepage coupled field of the embankment can be generated in time, so as to realize real-time detecting and deal with risks such as seepage failure. The infiltration time overlaps with the heating time. The temperature is higher with increasing heating power. However, the degree of temperature reduction is larger through the infiltration time with a higher heating power, as shown in Figure 14.  
Figure 14: Temperature distribution of optical fiber with concentrated seepage condition in unsaturated soil. Figure 13: Arrangement of optical fiber. It can also be noticed from Figure 15 and Table 1 that the greater the heating power, the better the effect of the optical fiber permeability measurement. For different heating powers, the greater the heating power is, the greater the temperature drop of the optical fiber caused by seepage is. For the unsaturated soil, the temperature drop is about 6.88 \({}^{\circ}\)C, while the drop is 3.96 \({}^{\circ}\)C when a concentrated seepage channel is formed. This means that in a natural state, the sensitivity of the optical fiber is greater than in a saturated state as the heat taken by seepage is greater in the former state and the temperature drop is greater.