Recent advances in subgrade engineering for high-speed railway

In the last decade, the design and construction technologies of subgrade in high-speed railway developed significantly. This paper reviewed corresponding development in five aspects, including mechanical properties of fill materials, dynamic performance of subgrade, foundation treatment, retaining structure and smart construction technologies. It showed that for unbonded granular materials, it was acceptable to use static strength for subgrade design, but for clayey soil it would be more appropriate to base on shakedown theory. The mechanism for lime modified clay has been thoroughly reviewed, and the effect of lime content, curing age, and curing conditions on the behavior of lime-treated clay was discussed. The dynamic response of subgrade, especially the long-term deformation and dynamic stability analysis were important to understanding the behavior of high-speed railway subgrade. The effect of track types, operation speed etc. on the dynamic response of subgrade were reviewed first. Then, the prediction methods, influencing factors, and corresponding issue for long-term deformation of subgrade were presented, following by the methods used for dynamic stability analysis. Three types of foundation treatment methods, including geosynthetic-reinforced pile-supported embankment, pile-raft structure, and pile-plate structure, were reviewed for the corresponding load transmission mechanism, and application scenario. The static and dynamic behavior of four types of retaining structures were presented, including cantilever retaining wall, geosynthetic reinforced soil retaining wall, anchored retaining structure, and retaining wall reinforced by soil nailing. Finally, a series of new technologies correlated to smart construction was introduced, relating to the survey, design, construction, detection and management of subgrade.