Long-term dynamic stability of improved loess subgrade for high-speed railways

Loess material requires improvement before being used as a filler for the bottom layer of the subgrade bed and substructure of a high-speed railway. Currently, cement and lime are often used to improve loess in engineering. However, whether improved loess material and the solution of key problems of the different types of improved loess can meet the long-term dynamic stability requirements of the bottom layer of a high-speed railway subgrade needs further study. Dynamic triaxial tests on cement-improved (CI) and lime-improved (LI) loess specimens were conducted to study the cyclic shear strain threshold and critical dynamic stress and to evaluate the long-term dynamic stability of CI and LI loess as fillers for the bottom layer of a subgrade bed. The results showed that the two improved loess materials can meet the long-term dynamic stability requirements when used as the bottom layer of a high-speed railway subgrade. After comprehensive consideration, 5% cement or 6% lime is recommended, with the CI soil prioritised. Compared with the critical dynamic stress method, the dynamic shear strain evaluation method is a more systematic and comprehensive method for evaluating the long-term dynamic stability of roadbeds. The research results can provide a technical reference for subgrade filler selection and subgrade design in a loess area.