Abstract: Tropical soil slopes are highly susceptible to geological disasters such as collapses and landslides under extreme weather conditions. Therefore, microbial-induced calcium carbonate precipitation (MICP) is considered an environmentally friendly method for slope stabilization. Following large-scale cultivation of Bacillus pasteurii, a combination of drip and sprinkler irrigation was applied for on-site reinforcement of tropical soil slopes. The reinforcement effect and solidification mechanism of typical yellow clay in tropical soil slopes were investigated through macro, micro, in-situ tests and laboratory tests. After on-site reinforcement with different dosages of MICP bacterial solution, subsequent tests were conducted accordingly. In-situ tests included rebound test and penetration test. Laboratory tests included calcium carbonate generation, unconfined compressive strength test, direct shear test, permeability test, as well as observations via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results show that: (1) The surface strength and penetration strength of the reinforced soil have been significantly improved, and they increase with the dosage of bacterial solution. However, the strength is discrete, indicating the reinforcement is uneven. (2) The compressive strength characteristics of the soil have also been improved to a certain extent. The compressive strength characteristic indexes have the largest increase and the most obvious change at the medium reinforcement strength. (3) With the increase of bacterial solution dosage, the shear strength gradually increases, and both the internal friction angle and cohesion rise, contributing to effective soil consolidation. (4) In terms of anti-seepage performance, permeability coefficient decreases by up to 63.5%, mitigating slope erosion and degradation caused by rainfall. (5) Through SEM-EDS observation, three specific reinforcement forms of calcium carbonate crystals on soil particles are obtained and proved by quantitative analysis. Therefore, MICP treatment can significantly improve the strength properties of clay and effectively enhance the stability of the slope.

Key words: microbial induced calcium carbonate precipitation (MICP), unconfined compressive strength test, direct shear test, microscopic observational analysis