Mechanical Properties and Mechanism Analysis of Yeast-Stabilized Loess

To expand bio-mediated stabilization to deep loess deposits under oxygen-deficient conditions, this study evaluates a non-ureolytic, yeast-based strategy under aerobic and anaerobic curing. Cylindrical loess specimens were prepared using a single-mix method by combining an activated yeast suspension with a cementation solution containing 0.05 M pyruvic acid and 1.0 M calcium lactate, and then cured for 3–28 days by film wrapping (aerobic) or vacuum sealing (anaerobic). Mechanical performance was quantified using unconfined compressive strength (UCS) and unconsolidated–undrained triaxial tests, and the strengthening mechanism was assessed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and carbonate-content quantification via acid washing. Relative to untreated loess (UCS = 81.3 kPa), yeast treatment increased UCS to 99.8–109.9 kPa under aerobic curing and to 89.1–95.7 kPa under anaerobic curing, demonstrating measurable reinforcement under anaerobic conditions. Mohr–Coulomb interpretation indicates that the strength gain is mainly attributed to an increase in cohesion from 25.3 kPa to 31.0–33.0 kPa, whereas the friction angle remains nearly unchanged (37–39°), suggesting a bonding-dominated response. SEM reveals fibrous/film-like bridging networks between particles, while XRD and carbonate measurements show negligible formation of new crystalline CaCO₃. Overall, yeast enhances loess strength primarily through polymeric cementation (EPS-like products) rather than carbonate precipitation, providing a promising and environmentally friendly option for deep-soil stabilization in anaerobic environments.