Premix–spray biomineralization method for anti-disintegration improvement of granite residual soil

Granite residual soils are highly susceptible to softening and disintegration when exposed to water, extremely easy to cause geological disasters. Biomineralization can be a promising method to improve the anti-disintegration of granite residual soils. However, due to the low permeability of the soil, it may be difficult to effectively or efficiently improve the anti-disintegration of granite residual soils using conventional premix or spray methods. This study proposes a premix–spray biomineralization method to improve the anti-disintegration of granite residual soils. The bacterial suspension, bioslurry, and crude soybean urease solution were used as the urea hydrolysis media in this study. The biomineralization of granite residual soils by premix, spray, and premix–spray methods was compared based on the disintegration test and calcium carbonate content measurement. The scanning electron microscope observation, energy-dispersive X-ray spectroscopy, and X-ray diffraction were also conducted to clarify the microscopic characteristics of the biotreated granite residual soils. The test results indicate that the premix–spray method could effectively improve the anti-disintegration of granite residual soil, and the bioslurry is the optimal urea hydrolysis medium for the premix treatment. The sample prepared by premixing with bioslurry followed by 3 cycles of spray treatment could remain relatively stable with no apparent disintegration or cracking within 24 h of immersion. The underlying mechanisms for the anti-disintegration improvement of granite residual soils with biomineralization may mainly include the pore filling, encapsulating bonds between soil particles, and biocementation of adjacent soil particles by the precipitated calcium carbonate crystals.