Effect of stress path on the shear response of bio-cemented sands

Bio-mediated techniques have the potential to be an eco-friendly and sustainable solution for engineering problems in the presence of unfavorable soil conditions. During the microbial induced carbonate precipitation (MICP) process, calcium carbonate is the byproduct of a series of biological and chemical reactions in the soil media. Although the shear response of MICP-treated sands with different calcium carbonate content has been extensively investigated, the behavior of this material subjected to varying stress paths with different levels of cementation and particle sizes is still unknown. In this study, the material behavior of MICP-treated sands under axisymmetric compression, radial extension, constant p', and constant q stress paths at moderate and heavy level of cementation is evaluated by conducting drained triaxial tests on specimens with relative density of about 40%. Shear wave velocity was measured during the course of treatment and shearing to monitor cementation and degradation processes. In addition, the effect of stress relaxation and compression after bio-treatment on shear response is evaluated. A previously proposed nonlinear failure envelope for MICP-treated sands is also verified by comparing the shear and normal stresses at failure with those predicted by the nonlinear failure envelope.