A study on the enhancement of the mechanical properties of weak structural planes based on microbiologically induced calcium carbonate precipitation

The advantages of outstanding economic efficiency and green environmental protection have positioned microbially induced technologies among the most promising reinforcement methods for structural planes. In this work, the enhanced mechanical properties of a weak structural plane at Baihetan Hydropower Station in China are investigated after microbially induced calcium carbonate precipitation. Sporosarcina pasteurii is actively cultured, and a standard curve relating bacteria concentration and optical density is developed. The curves of bacterial growth and urease activity are then investigated. Microbial reinforcement of weak structural plane specimens is conducted. The mechanical properties of weak structural planes are tested after reinforcement, and effects of bacteria concentration on the uniaxial compressive, shear, and triaxial compressive strengths are discussed. Based on XRD, EDS, and SEM analyses, the product of the microbially induced process is found to be calcium carbonate crystals, which measure approximately 510 mu m. It is observed that the crystals are well grown and distributed around particles in the weak interlayers. These particles are gradually encapsulated by induced crystals and finally cemented with interfaces of the tuff. The results also reveal that maximum increments of 148, 130, 192, and 114% of the uniaxial compressive strength, triaxial compressive strength, cohesion, and friction angle of the rock mass, respectively, can be obtained by adopting the microbially induced reinforcement method. It is expected that this paper can provide theoretical support for the reinforcement of structural planes of rock masses via ecologically green methods that save energy and reduce emissions.