Study on the mechanical properties and resistance to wetting–drying cycles of red clay stabilized by enzyme-induced carbonate precipitation (EICP)

In view of the problem of strong water sensitivity and susceptibility to dry and wet alternating damage of red clay, this study proposes to use plant-source enzyme-induced carbonate precipitation (EICP) technology for eco-friendly stabilization. Through a series of tests such as ratio optimization, triaxial shear and dry and wet cycle, the mechanical properties and durability of cured red clay were quantitatively evaluated, and its microphysical curing mechanism was revealed in combination with SEM and EDS tests. The results showed that the maximum catalytic activity of soybean urease was achieved at pH 8.0 and an incubation temperature of 55 °C. When the optimal ratio of 60 g/L urease and 1.0 mol/L cementation solution was used, the calcium carbonate content produced was the highest, and the improvement of unconfined compressive strength (UCS) was the most significant. These two parameters exhibited a strong positive correlation. The mechanical property test results show that EICP treatment significantly improved the compression modulus of the stabilized soil. The shear damage pattern of the treated soil showed typical strain hardening characteristics, and the effective cohesion increased from 18.12 kPa for the untreated soil to 43.14 kPa for the stabilized soil. The evaluation of the durability of the dry and wet cycle shows that after 20 cycles, the surface crack ratio of the stabilized specimens was only 5.2%, and the total mass loss is less than 5%, showing excellent volume stability and anti-collapse ability. SEM and EDS analysis show that the micro-nanometer calcium carbonate crystals induced by biochemical reactions effectively fill the capillary seepage channel inside the soil and build a strong bonding network between the scattered clay particles. Based on detailed indoor test data, this study fundamentally clarifies the intrinsic mechanism of EICP technology to effectively enhance the mechanics and durability of red clay.