Study on healing technique for weak interlayer and related mechanical properties based on microbially-induced calcium carbonate precipitation

The weak interlayer refers to the filling material in shear belts or large-scale structural planes, which is usually composed of soil, fine sand and gravels. It is prone to argillization when encountering water and its mechanical strength and stiffness are generally low, which has adverse effects on the stability of underground structures. In recent years, research on reinforcement techniques for weak interlayers has been a hot topic in geotechnical field. As a new reinforcement method for structural planes, the microbial healing technique has attracted a lot of attention. In this paper, a study on the healing technique for weak interlayer based on microbially induced calcium carbonate precipitation (MICP) and related mechanical properties was conducted for the interlayer shear belt at Baihetan Hydropower Station in China. First, Sporosarcina pasteurii was activated in laboratory. Reinforcement of the weak interlayer was realized by utilizing calcium carbonate precipitation on the weak interlayer. Continuous monitoring of the precipitates on the weak interlayer by XRD and SEM indicated that the precipitates on the weak layer were microbially induced calcium carbonate. Its crystals were irregular fish scale-shaped cubes with size in the range of 5~20μm. With favorable crystal growth, the crystals and the particles of the weak interlayer were cemented together. Finally, the mechanical properties of the healed weak interlayer were tested and the variations of uniaxial compressive strength, shear strength and triaxial compressive strength with bacteria concentration were discussed. The test results indicated that the maximum uniaxial compressive strength, peak shear strength and triaxial compressive strength can be increased by 149%, 162% and 119%, respectively, which subsequently improve the overall strength of the shear zone or structural plane. This can provide a new idea for soft ground reinforcement in underground projects.