Investigation on the mechanical and vibration isolation properties of rubber particle-flowable fly ash subgrade prepared with waste tires

In order to solve the problem of subgrade and foundation vibration damage induced by the railway train, a new type of rubber particle-flowable fly ash (FAR) subgrade was designed based on the principle of damping energy dissipation. The FAR material was prepared to meet the requirements of the working performance by the laboratory test, and the mechanical properties were investigated. The damping ratio characteristics of the FAR material were studied by the transient excitation method, the influence of the rubber particle content on the damping characteristics of the FAR material was analyzed and the vibration isolation mechanism of the FAR material was revealed. A 3D numerical model of track-subgrade-foundation was established by the finite element software, and the vibration isolation performance of the FAR subgrade was analyzed based on the coupled model. The results show that the rubber particles reduce the strength and dry density of the FAR subgrade. And the basic mechanical properties of the subgrade can meet the requirements of railway engineering application when the rubber particle content does not exceed 15% of the mass of solid mixture. The damping ratio of the FAR subgrade increases linearly with the increase of the rubber particle content. And the smaller the rubber particle size is, the larger the damping ratio of the FAR subgrade will be. On this basis, it is recommended to use the rubber particles with particle size of 150 mesh and particle content no more than 15%. The new subgrade is recommended for subgrade filling below the surface layer of the subgrade bed. Compared with the ordinary subgrade, the dynamic stresses of the subgrade bed bottom layer, subgrade soil and foundation soil of the FAR subgrade are reduced by 10%- 30%. In the main frequency range of the FAR subgrade vibration, the ground vibration acceleration level is generally reduced by 2-6 dB and the reduction is up to 83 dB, which verifies the good vibration isolation performance of the new FAR subgrade.