Shear Behavior of Biochar-Amended Biocemented Calcareous Sand Treated by Biostimulation

Biostimulated microbially induced carbonate precipitation (MICP) is an innovative soil improvement approach utilizing indigenous ureolytic microbes to hydrolyze urea. The objective of this study is to investigate the effect of biochar amendment on the shear strength of biocemented calcareous sand through the biostimulation approach. Biochar powder produced from softwood forestry residues with a maximum size of 0.045 mm was used. The specimens were prepared at two initial relative densities (i.e., 16.2% and 54.6%) and four biochar contents (i.e., 0%, 0.1%, 0.3%, and 0.5% by weight), and a series of direct shear tests were conducted at five normal stress levels (i.e., 50, 100, 200, 400, and 600 kPa). The cementitious content, peak shear strength characteristics, and microstructural features were determined during and at the end of the tests. The results indicate that the amendment of biochar in biocemented sand could increase its overall cementitious content. It is also found that whether biochar amendment could enhance shear strength depends on the biochar content, cementitious content, and initial relative density. The higher initial relative density (54.6%) and moderate biochar content (0.3%) are favorable conditions for greater sand shear strength enhancement provided by biochar. Microscopically, the biochar powders are embedded within biocementation. Mechanistically the effects of biochar on the shear strength of biocemented sands are (1) increasing cementitious content, (2) creating weak points inside biocementation, and (3) reducing interparticle friction.