Study on the effects of biochar on the soil-water and soil-freezing characteristics of a compacted silty clay

Biochar, an eco-friendly material, has been extensively utilized in agriculture, environment and energy sectors. Many studies in the literature have concluded biochar’s efficacy in modifying soil physicochemical properties and water retention capacity. However, the impacts of biochar on the behaviors of engineering soils under unsaturated and frozen conditions have been much less investigated or understood. To close these gaps, the effects of a corn straw biochar on the basic geotechnical properties, water retention and freezing characteristics of a compacted silty clay were comprehensively investigated in this study. The test results show that the biochar used in this study has a highly porous structure and abundant surface functional groups, which markedly influence the physicochemical properties and water retention behavior of the compacted silty clay. The rich pores and functional groups of the biochar changed the soil particle-pore water interaction, resulting in a relatively stable and complicated multiphase system that has higher water holding capacity, under both unsaturated and frozen conditions. In addition, the change of the behavior of the silty clay with biochar adding was found also related to biochar dosage and particle size. The outcomes of the present study can improve our understanding of how biochar influences the engineering behavior of soils and provide a basis for its broader application in cold and arid regions.