Optimization of biomineralization process parameters for granite residual soil and its anti-disintegration

Granite residual soil has a high content of hydrophilic minerals, is sensitive to water and easy to disintegrate when it comes into contact with water, making it a common soil type related to geological disasters (such as landslides). To improve the anti-disintegration of granite residual soil, the method of “premixing of urease bacteria-based bioslurry + spraying of soybean enzyme-based biotreatment solution” (referred to as “premixing-spraying” method hereafter) was used for the biomineralization of granite residual soil. The effect of three key parameters, including the premixing content of urease bacteria-based bioslurry, single spraying volume and the number of spraying rounds, on biomineralization were investigated, and the underlying mechanism of improving the anti-disintegration of granite residual soil by premixing-spraying method was discussed. The results show that increasing the premixing content of urease bacteria-based bioslurry can promote the precipitation of calcium carbonate in the soil and thus effectively improve its anti-disintegration, but the improvement becomes not obvious when the content exceeds 32%. Insufficient spraying leads to low calcium carbonate production, while excessive spraying causes the accumulation of excess calcium carbonate crystals on the soil surface, which will affect the subsequent calcium carbonate production in the soil. The optimal single spraying amount is about 100 L/m³ and the optimal frequency is 3 spraying rounds.