Influence of grain group deletion on the properties and pore-cementation synergistic mechanism of EICP-consolidated sandy clayey purple soil

Soil erosion, a critical global environmental challenge, is exacerbated by the structural vulnerability of sandy clayey soils. This study investigates the influence of enzymatic calcium carbonate precipitation (EICP) on the consolidation of purple sandy clayey soil under conditions of specific particle size fraction deficiency. Utilizing response surface methodology (RSM), calcium carbonate content analysis, unconfined compressive strength (UCS) testing, soil permeability measurements, and nuclear magnetic resonance (NMR) pore structure analysis, we assessed changes in soil compressive strength, permeability, aggregate stability, and pore structure for different deficient size fractions (0.500-0.250 mm, 0.250-0.075 mm, 0.075-0 mm). Results identified optimal EICP grouting concentrations for soil solidification as 51.68 g/L urease, 0.67 mol/L calcium acetate, and 0.58 mol/L urea. Complete gradation enabled uniform cementation, yielding the optimal property combination: maximum compressive strength (250 kPa), minimum permeability coefficient (4.92 × 10 -5 cm/s), and highest aggregate stability. The absence of the coarse fraction (0.500-0.250 mm) compromised cementation pores, resulting in moderate strength reduction. Deficiency in the medium fraction (0.250-0.075 mm) significantly increased permeability and structural fragility. Conversely, the absence of the fine fraction (<0.075 mm) led to cementation failure and substantial property deterioration. This study elucidates the synergistic mechanism of gradation-porosity-cementation, providing theoretical support for erosion control, ecological slope stabilization, and soil health management in purple sandy clayey soils.