Undrained shear strength of biochar-assisted biocemented calcareous sand by biostimulated microbially induced calcium carbonate precipitation

Abstract

Biostimulation has been proven to be an available approach for microbially induced calcium carbonate precipitation (MICP). However, biostimulation may not be as effective as bioaugmentation in some unfavorable situations. In this study, the feasibility of biochar-assisted MICP for improving the shear strength of calcareous sand is investigated. The optimization of cementation solution for biostimulated MICP is first determined through a series of unconfined compressive tests. The shear characteristics of biocemented calcareous sand, enhanced by biochar and treated through biostimulation, are then assessed using consolidated undrained (CU) shear triaxial tests. To characterize the shear strength of biocemented sand under low effective normal stress, both Mohr-Coulomb failure envelopes and nonlinear failure envelopes were employed. Meanwhile, the current study also compared and analyzed two distinct stress states: maximum principal stress ratio ((ð1/ð3)max) and Skempton’s pore pressure parameter A ¼ 0, to identify an appropriate failure criterion for determination of the shear strength parameters. Furthermore, the microscopic features and post-failure characteristics of biochar-assisted calcareous sand were examined and discussed. The findings indicate that biochar can contribute to an increase in cementation content by serving as additional nucleation sites. The study may provide valuable insights into the potential of biochar-assisted MICP for enhancing the biostimulation approach.