The use of recycled materials is a new tendency in the field of railway engineering. Steel slag aggregates (SSA) are one of the recycled materials derived from the steel industry. The application of SSA in ballasted railway tracks requires mechanical examination. In the present paper, the shear behavior of the ballast layer constructed by SSA and basalt aggregates was considered to assess the use of SSA as a substitution for basalt. In this regard, a series of large-direct shear tests were performed on basalt and SSA under various normal stresses. Based on the results, basalt aggregates have higher shear resistance than SSA for all normal stress. However, steel slag has sufficient shear strength as well as particle abrasion resistance. Overall, it was proven that the SSA has suitable stability against shear forces that could be applied on railway ballast.

In this study, the application of a retaining wall was proposed as a solution for reducing the lateral displacement of the ballast layer, particularly in sharp curves and bridges. In this regard, a series of single tie push tests were performed on panels with shoulder ballast widths of 300 mm, 400 mm, 500 mm with and without the presence of L-shaped and T-shaped retaining walls. Overall, it was proven that the application of an L-shaped wall led to a 15.8% increase in the lateral resistance, and that T-shaped walls have a higher impact on the stability of the track. A shoulder width of 400 mm was proposed as the optimum width for ballasted tracks with retaining walls.