Abstract: The coarse-grained soil is widely used as the filling in the railway subgrade, which is directly subjected to the long-term effect of the dynamic cyclic train loads transmitted from the track structure. Investigation of its dynamic behavior and plastic deformation characteristics under the dynamic train loads may provide ideas for the subgrade performance evaluation and settlement control. GDS dynamic triaxial tests were used to investigate the dynamic response of coarse-grained soil in railway subgrade. By introducing the plastic strain rate and shakedown theory, the evolution law of axial plastic strain of subgrade under different frequencies, confining pressures and cyclic dynamic stress ratios is divided into three types: plastic shakedown, plastic creep and incremental plastic failure, based on which the critical dynamic stress levels of plastic shakedown and plastic creep state are determined. Results show that the critical cyclic stress ratio of coarse-grained soil increases with the increase of confining pressure, while decreases with the increase of loading frequency. Based on the fitting analysis of the experimental results, an empirical formula of critical dynamic stress with confining pressure as variable is proposed, which can provide theoretical basis for the dynamic stability evaluation of subgrade at any depth.

Key words: GDS dynamic triaxial tests, coarse-grained soil, axial plastic strain, critical cyclic stress, shakedown theory