Mechanism of improvement of biochar on shear strength and liquefaction resistance of sand

Biochar is a biomass-derived carbonaceous solid product produced by way of pyrolysis, a process whereby thermal degradation of biomass occurs in the absence of or under a limited oxygen environment. To date, little work has been done to assess its effect on soil properties from the geotechnical point of view. A few studies have shown that biochar could increase the shear strength of clays. Results of simple shear tests indicated that although the effect of adding biochar on the drained shear resistance of sand is relatively minor, the liquefaction resistance increased considerably. In this paper, to provide an insight into the mechanism, the interaction between biochar and water was studied in more detail, through an analysis of the biochar chemical active surface, morphological observations of the particles and biochar–water suspension, as well as rheological measurements. It is believed that the mechanism of improvement is related to the active chemicals on the surface and inside the pores of the biochar particles. These volatiles interact with water by repelling it (hydrophobic) and at times by attracting it (hydrophilic), creating a complex network between water and biochar particles that helps to delay the increase in excess pore-water pressure and provides some shear resistance.