## 5 Conclusions  
In this study, a six-degree-of-freedom mathematical model of a \"five-point-contact\" aircraft was established, and the vibration balance equation of the mathematical model was deduced. Using ABAQUS software as a platform, a 3D finite element calculation model of the airport pavement-soil layer-tunnel was formulated to study the variation law of tunnel structures under airport runways due to different influencing factors. The main conclusions are as follows.  
1. Different types of main landing gears have various forms and dynamic load equations because of the variations in tire pressure, number of wheels, and single wheel load. The distribution position of the main landing gear wheels also affects the structural force; a more concentrated wheel distribution causes greater interference to the structure. The roof position of the tunnel structure is stretched, and the vertical acceleration change range can reach 259% under the action of aircraft loads. This position is a damage-prone section that must be considered in the design.
2. Rigid pavements have large elastic moduli and are not easily deformed when subjected to aircraft loads. For the pavement substructure, flexible pavements have a satisfactory attenuation effect on force transmission. In the airport substructure design, the flexible pavement can be selected as the airport runway to ensure safety. The shear stress at the upper and lower arches of the tunnel structure varies depending on the road surface material. Moreover, relative dislocation and deformation occur at the arch. Owing to the differences in pavement materials, the shear stress on the structure varies, and the deformation at the arch is more severe than at other positions.
3. The interference effect of aircraft loads on the structure gradually weakens with increasing embedment depth. However, the soil stress on the tunnel structure increases with the burial depth, and the degree of interference of the soil stress on the structure is greater than that of the aircraft load. Therefore, during construction, the selection of corresponding support methods to cope with various soil depths and environments is necessary. The fitting curve indicates that when the burial depth exceeds 64 m, the movement of aircraft on the runway above does not affect the buried tunnel.  
Conceptualization, L.Y.; methodology, X.W.; software, J.F.; formal analysis, G.L.; data curation, X.S. and S.B.; writing--original draft preparation, L.Y.; writing--review and editing, L.Y.; visualization, X.W.; project administration, X.W.; funding acquisition, G.L. and X.W. All authors have read and agreed to the published version of the manuscript.  
Figure 15: A fitted prediction curve; (**a**) peak vertical displacement of the roof; (**b**) fitted prediction curve.  
**Funding:** The work described in this paper was supported by National Natural Science Foundation of China (M.Z., Grant No. 41902266), the Central Plains Science and Technology Innovation Leading Talent Project (X.W., Grant No. 194200510015), the Training Plan of Young Key Teachers in Colleges and Universities of Henan Province (X.W., Grant No. 2021 GGJS116), the Key research Project of higher education institutions in Henan Province (X.W., Grant No. 23A440002).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.