Microbially induced carbonate precipitation for improving the internal stability of silty sand slopes under seepage conditions

Biocementation based on the microbially induced carbonate precipitation (MICP) process can be used as a soil improvement method to improve the mechanical strength of granular soils. In this study, triaxial consolidated drained (CD) tests and constant shear drained (CSD) tests were carried out to evaluate the applicability of MICP as a method to mitigate suffusion and improve the internal stability of silty sands under seepage conditions. The CD test results demonstrated that biocementation is efficient in terms of strength improvement and deformation control of silty sand. The shear strength and the slope of failure line in p’-q plane increased with the number of treatment cycles at various levels of soil density. The CSD tests simulated the concurrent seepage-constant shear drained conditions that can trigger suffusion and instability of slopes. Results showed that the stress ratio q/p’ and the hydraulic gradient at which the biocemented samples became unstable were higher than those of the untreated samples, which suggests that biocementation can effectively improve the stability of soils under concurrent seepage-constant shear drained conditions. Additionally, the biocemented samples also have stronger resistance against suffusion compared with untreated samples showing lower amount of eroded fine particles. Suffusion resistance improved with the number of treatment cycles and soil density.