## 5 Discussion and Conclusions  
A multilayer structure composed of asphalt pavement and subgrade soil was simulated. The maximum reach of the tag signal was tested through a laboratory experiment. On the basis of limited laboratory test results, the maximum signal reach depth of the tag installed under the pavement structure was 68 cm. This is a performance that satisfies the target design depth of 40-50 cm. Even considering that dBm is a unit of a logarithmic scale, the signal attenuation at shallow depths was rapid, and RSSI levels at 68 cm, 65 cm, 60 cm, and 50 cm close to the limit point had a small width of decline. Based on the results of experiments by material, the signal-reaching performance in the graded gravel was the best. The signal attenuation was the largest in the subgrade soil, and the signal was not received in cement mortar. The difference in signal attenuation between the sand and the graded gravel was larger than the effect of 15 cm depth, and the difference between the subgrade soil and the graded gravel was even greater. Figure 5: A plot of signal attenuation by moisture contents. Figure 6: A test result of surface layer thickness. The results showed that the effect was due to the porosity and density of the material. This experiment was conducted for the purpose of testing representative materials used in road structures. If a more precise experiment is performed with the density or void as a variable, design criteria according to the material can be derived. In addition, signal attenuation of 1.8 dBm occurred according to moisture. When using permeable materials, the effect of signal attenuation due to moisture must be considered. Under the road structure, there are various facilities to provide functions of the city, such as communication lines, power lines, water supply and sewage, gas pipes, and heat transport pipes. Based on the investigation results of the management technology of underground utilities, electromagnetic locator, GPR, and RFID application technology were representative. All three were technologies utilizing electromagnetic waves. However, each had its pros and cons. Among them, UHF RFID tags were selected as an alternative to install on utilities, because they can provide information, have no battery restrictions, and have the least influence on the surrounding environment. To evaluate the performance and capability of the UHF RFID tag, a laboratory experiment was implemented. The main purpose of the experiment was to determine how deep a signal can reach in a multilayer road structure. According to advanced studies, the effect of signal attenuation is caused by the type and moisture of the medium. The key achievement of this study is that it reviewed the optimal installation depth. It can be obtained by finding the maximum reach depth of the signal in the road structure. In addition, the effect of signal attenuation according to the materials and moisture was examined. When installing a communication cable by trenching excavation, a suitable material was found that had a higher porosity, and lower moisture. In particular, conducting reach performance experiments in media primarily used in civil engineering fields, such as soil and asphalt could become a technical foundation for future applications to the underground utility history management system. Research limitations and further work are suggested as follows. First, it is necessary to overcome the limited experimental variables and lack of mock-up tests through field applications. In addition, theoretical analysis and simulation are needed. Second, signal attenuation should be analyzed considering the properties of each material and the interface. Voids and the density of the material and electromagnetic wave behavior at the different interfaces would affect the signal attenuation. Through this work, it would be possible to theoretically differentiate the characteristics between monolayer and multilayer mediums. Third, it is necessary to analyze the effect of the antenna used with tags.