Effect of wetting and drying cycles on the durability of bio-cemented soil of expressway slope

Abstract

Cyclic wet-dry is one of the influential weathering agents which can rapidly alter the mechanical properties of soils, limiting their durability and consistent performance. This study investigates the effect of wet-dry cycles on the mechanical behaviour of bio-cemented soil. Microbial-induced carbonate precipitation-based bio-cementation is an innovative soil improvement method, which is gaining increasing attention as a potential alternative for stabilizing slope surface. As the treated surfaces are exposed to repeated rainfalls and draughts, durability analysis is essential; cyclic wet-dry tests were therefore performed as a credible indicator of durability. The soil obtained from the Hokkaido expressway slope was treated at laboratory to varying cementation levels (% CaCO3) and subjected to 50 subsequent wet-dry cycles. Physical and mechanical changes were monitored using mass loss, shear wave velocities and needle penetration tests during wet-dry cycles. The results showed that the wet-dry cycles deteriorated the physical and mechanical at two stages. The mass and S-wave velocity of specimens significantly dropped after first few cycles and then tended to reach equilibrium. The second stage of notable deterioration was observed between 30 and 50 wet-dry cycles. It is suggested that the erosion of weak and powdery deposition of CaCO3 causes the degradation at the early stage, whereas the degradation in the late stage was attributed to the microstructural deformations of intact carbonate bonds. It was also found that the increase in cementation level decreases the deterioration of bio-cemented soil under wet-dry cycles.