Abstract:

Comfort and safety of moving train is directly determined by dynamic response and stability of railroad subgrade. In order to investigate behaviors of silt subgrade soils subjected to moving train loading, cyclic triaxial tests including conditions of soil compacting factor, water content, deviator stress, and loaded frequency were conducted in laboratory. Based on the test results and field measurements of subgrade stress during train loading, it is found that with train speed increasing, silt railroad subgrade should be stable if its natural moistness is near to optimum water content and compacting factor is not less than 0.9; moreover, if subgrade compacting factor is only 0.85 and deviator stress of subgrade surface is less than 70 kPa, subgrade is also stable; but it would lose stability at higher deviator stress level. With train speed increasing, the elastic deformation of subgrade rises linearly, but resilient modulus changes negligibly. With increase in saturation, the threshold stress and resilient modulus of subgrade decrease significantly, while the elastic strain and cumulative strain increase sharply; and it may result in failure of subgrade, so train speed should be limited in wet season in order to reduce subgrade deviator stress.

Key words: train speed-increasing, subgrade, silt, dynamic stability, cyclic triaxial test