To make steel slag being reasonably used in geotechnical backfilling projects or soft foundation treatment projects, three kinds of steel slag such as fine, coarse, and gravel steel slag were studied through particle analysis tests, relative density tests, and specific gravity tests to obtain basic physical parameters. Considering the influence of relative density, gradation, and other factors, constant head permeability tests of pure steel slag and variable head permeability tests of modified silt soil with different mixing contents of steel slag were carried out to test permeability coefficients under various working conditions. Prediction formulas on the permeability coefficients of the three kinds of pure steel slag and steel slag-treated silt soil were, respectively, deduced. It was concluded that the permeability coefficient of pure steel slag was greatly influenced by particle size and relative density, similar to the case of permeability coefficients of fly ash and fine sand in their dense states, and the larger the relative density was, the smaller the permeability coefficient was. The permeability coefficient of steel slag-treated silt soil increased with increasing of mixing content of steel slag, showing that steel slag can obviously improve the permeability performance of silt soil. Research results provide reference for design and construction on the application of steel slag in roadbed backfill, steel slag modifying silt soil, and other projects.

Waste steel slag is a recycled industrial solid waste and is sometimes used as backfills, but the dynamic shear properties of waste steel slag have not been researched at present. To understand the dynamic shear properties of waste steel slag, the resonance column tests were carried out to investigate the dynamic shear modulus and damping ratio of the steel slag considering the effect of the relative density of steel slag and confining pressure. The maximum dynamic shear modulus was discussed, and the dynamic model of the steel slag was constructed by the Hardin–Drnevich model. The regression analysis of the normalized dynamic shear modulus ratio and damping ratio of the steel slag showed that the dynamic model was very fit for the steel slag. The comparisons of the dynamic shear properties of the steel slag with those of Nanjing fine sand and Fujian standard sand showed that the steel slag had similar dynamic shear resistance to Fujian standard sand and had potential to become a substitute for sand in the practical geotechnical engineering in the future.

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