Dynamic response of subgrade under moving loads of main landing gears

The cyclic dynamic stress of runway subgrade soil induced by the moving loads of the main landing gears in the process of taking off and landing is the main cause of the settlement and differential settlement of runway. Based on the superposition principle, the dynamic responses of the subgrade soil under the moving loads of the main landing gears B747-400 and A380-800 are analyzed by using the semi-analytical finite element method. The results show that under the the moving loads of main landing gears of B747-400 and A380-800, the vertical normal stress of subgrade of shallow soil is inverted as the pot type distribution, and the load influence depth can be up to 13 m. The distribution of the main loading gears has a greater influence on the vertical normal stress of shallow subgrade soil than the deep subgrade soil. The moving speed of aircrafts has an obvious effect on the distribution of the vertical normal stress of deep subgrade soil. Under the taking-off speed of 60 ~ 80 m/s, the load influence depth is 1.5 ~ 1.7 times than that of the static analysis. Compared with that of the rigid pavement, the vertical normal stress of shallow soil increases by about 50% and the load influence depth increases by about 10% for flexible panel.