# Study of the Dynamic Response of a Rigid Runway with Different Void States during Aircraft Taxing
## 5 Conclusions  
This paper investigated the interaction between the aircraft and the runway during taxiing and developed a simulation model of the vibration system. In addition, the dynamic load of aircraft taxiing was calculated on the pavement, and the vertical dynamic displacement (VDD) response and the variation law of the runway under the action of a moving  
Figure 16: The change in the WPERs of frequency bands 1 and 3 of the signal at monitor point 3. Figure 17: The change in the WPEEs of frequency bands 1–4 of the signal at monitor point 3.  
load were investigated thoroughly. Simultaneously, the energy distribution characteristics of the wavelet packets of acceleration signals in various positions of the pavement slabs were extracted, and the relationship between the energy distribution of specific wavelet packets and void status was discussed. The findings are summarized below. 1. Using the simplified 4-DOF aircraft-runway coupled vibration model, runway pavement roughness was used as the load excitation source to calculate the dynamic load of the aircraft taxiing quickly and accurately, applying the state space method. 2. When the aircraft taxied on the normal runway structure, the peak VDD of the base layer decreased by only 7% compared with that of the runway surface layer. When the depth of the soil foundation was 2.1 m, the peak value of the VDD decreased by 53% compared with that of the surface layer. When the depth of the soil foundation was greater than 8.4 m, the change in VDD was not obvious. With the increase in depth, the position of the peak VDD gradually shifted to the runway center. In the depth range of 8.1-10.1 m of soil foundation, the position of the peak VDD shifted to the runway center by 3.2 m.
3. When the pavement was slightly void, the VDD (\(U_{Y,0}\)) calculated for the runway central point of the surface layer did not change obviously with the decrease in modulus reduction coefficient \(\xi\) in the hollowed area in the range of 1-0.1, but with the decrease in \(\xi\) from 0.1, \(U_{Y,0}\) increased sharply. On the whole, \(U_{Y,0}\) had a negative exponential relationship with \(\xi\). The vertical displacements of the lower surfaces of the left and right main landing gears (\(U_{Y,L}\), \(U_{Y,R}\)) were logarithmic with \(\xi\). When there was a severe void, \(U_{Y,0}\) decreased with the increase in void area SVA, and the overall relationship was exponential. \(U_{Y,L}\), \(U_{Y,R}\) decreased linearly with the increase in \(S_{VA}\). On the whole, \(U_{R,0}\) could better reflect the vacancy situation. 4. When the aircraft taxiing load acted on the rigid runway, the angular vibration response signal of the road panel caused by it was used. The wavelet packet energy characteristics of the signal, the ratio of the wavelet packet energy in the low-frequency band, and the entropy of the wavelet packet energy could be extracted, which could be used as the eigenvalues to identify the void condition of the runway pavement. According to the above research results, it can be seen that the dynamic displacement of the rigid runway concrete slab along the runway width direction and the wavelet packet energy ratio and wavelet packet energy entropy could be obtained from the acceleration signal of slab corner under the aircraft load. All of them could be used to reflect the supporting condition or void area of the pavement slab by the base layer. Therefore, embedded displacement sensors can be arranged at the lateral edge of the pavement slab, and embedded acceleration sensors can be arranged at the corner of the slab. In this way, it can be effectively sensed whether the runway panel has a void, as well as its degree, by using the taxiing effect of the aircraft without stopping the airport. This provides a new idea and method for the identification of airport runway slab voids and provides a certain reference value for the implementation of runway health monitoring. Conceptualization, H.X. ; methodology, G.H. ; software, G.H. and T.X. ; validation, P.L. ; investigation, P.L. and Y.M.