To assess the stabilizing effect of sodium alginate (SA) on cement soil subjected to dry-wet cycles, a comprehensive study was conducted involving UCS tests, dynamic triaxial tests, SEM analysis, and XRD analysis. The results showed that after 11 dry-wet cycles, the residual strength of the cement soil was 11.25 kPa with a 90.1% strength loss rate, while the SA-modified soil had a 72% loss rate and a residual strength of 432 kPa. Dynamic strain increased and dynamic elastic modulus decreased with higher dynamic stress, while higher loading frequencies reduced dynamic strain and increased dynamic elastic modulus. Increased cycle counts led to higher dynamic strain and lower dynamic elastic modulus. The damping ratio curves shifted downward with higher frequencies and moved rightward with more cycles. SEM and XRD analyses revealed that SA formed reticular cementitious materials that encapsulated soil particles and aggregated fines into larger particles. Sodium alginate significantly enhanced the soil's resistance to dry-wet cycles, providing valuable insights for coastal and soft soil subgrade engineering design.

Biocrust has many ecological roles and the potential for land restoration. Major obstacles to biocrust inoculation in degraded areas are the low physical stability of soil and the frequent wet-dry cycle. Microbially induced carbonate precipitation (MICP) technology, a sand fixation technique, can increase soil stability and decrease soil evaporation. However, it is unclear what the ecological influence of MICP treatment is under the harsh environmental stress. We hypothesized that MICP-treated soil could support biocrust establishment by moderating soil disturbance and improving water retention to mitigate frequent wet-dry cycles. To verify this hypothesis, we prepared cyanobacterial biocrusts (Oscillatoria tenuis) on bare soil and on MICP-treated soil (Sporosarcina pasteurii) and cultivated them for 40 days under high- and low-frequency rainfall. We also simulated disturbance at zero, half, or equal (0, 75, and 150 kJ) the intensity of field conditions during the cultivation. Generalized linear modeling revealed that cyanobacterial biocrust with MICP treatment had high wind erosion resistance but had low indicators of biocrust growth. We also found that MICP treatment facilitated the reduction in chlorophyll content by frequent rainfall and that MICP treatment and physical disturbance had no clear interacting effects on biocrust properties. In summary, our study found MICP treatment could hinder rather than support the cyanobacterial biocrust establishment under the frequent watering and heavy disturbance. Our finding suggests that the appropriate combination of rehabilitation techniques depends on the environmental characteristics of the target area.