Abstract: To expand the application of biochar in civil engineering, biochar was used to partially replace cement in biochar-cement soil. The permeability characteristics and mechanism of biochar-cement soil with different biochar contents and curing ages were analyzed using the falling head permeability test and scanning electron microscope (SEM) test to determine the optimal biochar content. The permeability test results showed that the permeability coefficient of cement soil decreased first and then increased with the increase of biochar content. The lowest permeability coefficient was observed when biochar replaced 1% of the cement. Additionally, the permeability coefficient of cement soil decreased nonlinearly with the increase of curing age, and biochar had the greatest influence on permeability of cement soil in the early stage. Meso-structure analysis revealed that biochar did not participate in chemical reactions within the cement soil. Biochar improved the anti-permeability performance of cement soil by filling the pores between soil and cement particles, making the mixture more compact.

Key words: biochar, cement soil, permeability, falling head permeability test, scanning electron microscope test, meso-structure