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In order to promote the sustainable use of oil shale residues, a novel subgrade material (SOF) composed of silty clay, oil shale ash residue, and fly ash was developed. The aim of this paper is to study the mechanical behavior and environmental impact of SOF, which is regarded as the safety assessment and prediction for the application of this novel material. To this purpose, the road performance, dynamic properties, and environment impact tests are conducted. In terms of the road performance, the test results of SOF exceed the standard requirement, especially for CBR (California bearing ratio), which can maintain good performance at bad conditions of low compaction degree and being soaked for a long time. The dynamic properties under cyclic loadings are better than most of original and stabilized soils. The shear strength parameters and the anti-damage mechanism are also discussed; research results show that the friction of SOF mostly contributes to shear strength under high stress conditions, while its cohesion tends to play a more important role under low stress conditions. According to the deformation variation, the accumulation settlement of SOF under vehicle loadings after several years is predicted, which is far lower than the limit of expressway and Grade I highway. Furthermore, the chemical stability and toxicity of SOF leachates are environmentally friendly, which are in line with the benchmarks of Class II surface water and Class III ground water. All the experimental results manifest that SOF used as subgrade filling has good application potential and safety.

Silty clay modified by fly ash and crumb rubber has been proven to have potential as a subgrade filling in frozen areas due to its steady strength after freeze–thaw cycles and outstanding thermal insulation. To understand the freezing characteristics of this novel modified soil, its freezing temperature was measured as an evaluation index. An improved method using a Beckman thermometer was adopted to obtain the freezing temperatures from freezing curves. The freezing curves of silty clay, fly ash soil (silty clay modified by fly ash) and the modified soil (silty clay modified by fly ash and crumb rubber) with different water contents were determined. The influence of fly ash and crumb rubber on the freezing temperature of silty clay was investigated. The results indicated that the characteristics of the freezing curves of the test soils differed slightly, particularly in terms of the freezing temperatures and freezing rates. Fly ash can be applied to decrease the freezing temperature of silty clay, whereas crumb rubber increases the freezing temperature slightly. Three empirical equations without considering the effect of fly ash and crumb rubber were developed to calculate the freezing temperatures of the test soils.