Dynamic Characteristics of Soil Subgrade Bed for Ballastless Track

In order to study the nonlinear elastic properties of the deformation modulus and reaction coefficient of soil subgrade bed, a large-scale test model of ballastless track subgrade and a comprehensive field test were used to analyze the static and dynamic characteristics of the ballastless track subgrade before and after rainfall under step static and dynamic loading. The result indicates that along the transverse direction in the subgrade cross section, both the static response and dynamic response have a saddle-shaped distribution. The largest static response and dynamic response measured are under the concrete base slab at the track position, while the responses under the centre-line and two ends of the concrete slab are small. The most intense dynamic responses are measured in the surface layer of subgrade bed （graded gravel area）, and they reduce sharply with depth. Compared with before rainfall, the subgrade static stress, dynamic stress, acceleration, and dynamic deformation increased about 12%, 3%, 35%, and 13%, respectively, at most after rainfall. Therefore, sufficient emphasis should be placed on the waterproofing and drainage measures.