Advanced hydraulic characteristics of treated and untreated Bauxite Residue (Red Mud) are studied and compared using a Steady-State Centrifugation (SSC) Unsaturated Flow Apparatus (UFA). Red Mud is the by-product waste from the Bayer process during aluminum production that has shown the potential of being reused as fill material in embankment construction, which can reduce the energy consumption of disposing the minging waste and producing fill materials. There is a limited number of documented studies on unsaturated hydraulic characteristics of RM. Furthermore, the high alkalinity (pH > 12) of the bauxite slurry is a challenge for reusing the material. Past studies have shown two effective and economic neutralization methods: (i) mixing with seawater and (ii) addition of gypsum. This study utilizes Cal State LA centrifuge facilities to characterize the unsaturated hydraulic properties of the treated and untreated Red Mud. The experimental results are used to develop the Soil Water Retention Curve (SWRC) for the three types of Bauxite Residue: untreated, treated with saline solution, and treated with gypsum. The results show that adding gypsum is more effective than mixing with saline solution in reducing the pH value of RM, and the samples treated with saline solution provide the lowest range of unsaturated hydraulic conductivity values compared with the other two types.

Recycled materials like Bauxite Residue (Red Mud) and Fly Ash are prevalent in recent feasibility studies on reused materials in geotechnical engineering applications. Red Mud is a mining waste from aluminum manufacturing, and Fly Ash is a by-product of coal combustion in power plants. Nevertheless, to fully reveal the feasibility of using those materials for constructing above-ground earth structures, a better understanding of their unsaturated performance in geo-structure is essential. While some popular empirical models (e.g., van Genuchten 1980) in Soil Water Retention Curves (SWRC) are commonly used to describe soils' unsaturated conditions, those models may not apply to unique materials like Red Mud and Fly Ash. Recently, SWRC curves of both materials were acquired through the Steady-State Centrifuge (SSC) Unsaturated Flow Apparatus (UFA) procedure at Cal State LA. The experimental data were used to develop analytical models following the van Genuchten model. Using a finite-difference software (FLAC) and obtained SWRC curves, this study performed numerical simulations of embankments filled with Fly Ash and Red Mud, comparing it with an embankment filled with typical silty soil with the same dimensions and conditions. Results showed seepage flow rates for Fly Ash and Red Mud are higher when used as fill material as above-ground embankments.

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