Dynamic properties and environmental impact of waste red mud-treated loess under adverse conditions

Under the combination of heavy loading and high moisture content, the metastable structure of natural loess can easily lead to uneven settlement and damage the overlying infrastructure. Using traditional binder such as cement has harmful impact on the environment, especially due to resource consumption and carbon emission. This research has identified the feasibility of using red mud waste as a partial replacement of cement for loess subgrade treatment in terms of dynamic properties and environmental impact. The performance of loess treated with a combination of waste red mud (RM) and small amount of cement additive (C) is evaluated by considering the complex engineering geological conditions. The results show that dynamic stress (σ_d) and moisture content (w) have a more significant influence on the dynamic properties of RMC-treated loess compared with confining pressure (σ₃) and loading frequency (f). Higher w shows a remarkable reduction in the dynamic load resistance of treated loess, yet the addition of RMC still can improve the microstructure and water sensitivity of loess. Specifically, the failure dynamic stress (σ_df) and the maximum dynamic elastic modulus (E_dmax) of the treated loess at higher w are found to be 100% and 400% higher than those of untreated loess respectively. RMC treatment also improved the dynamic cohesive (c_d) value from 23.2 to 173.6 kPa compared with untreated loess. In addition, the leaching toxicity and radiation of RMC-treated loess indicate that it does not pose any risk to the groundwater. Finally, revised Monismith model has been developed based on the proposed formula for predicting power index b, which can be capable of describing the long-term deformation stability under cyclic loading.