Multi-model validation of the hydro-mechanical and soil–water characteristic behaviour of a slag-cement-amended iron ore tailings– bentonite liner material across compaction moisture states

Abstract Compacted liners made from iron ore tailings (IOT) and bentonite must satisfy strength, hydraulic and shrinkage criteria concurrently, yet these properties respond in opposing directions to the compaction water content. This study evaluates how the compaction moisture state (2% dry of optimum, DOPT; optimum, OPT; 2% wet of optimum, WOPT) governs the performance of IOT–bentonite mixtures (20–40% bentonite) stabilised with 0–10% slag cement (CEM III), compacted at British Standard Heavy (BSH) energy and cured for 28 days. Unconfined compressive strength (UCS), saturated hydraulic conductivity ( K sat ) and volumetric shrinkage ( V s ) were measured for 25 mixtures, and Gaussian process regression (GPR) was used to map the combined compliance region against UCS ≥ 200 kPa, K sat ≤ 1 × 10 − 9 m/s and V s ≤ 4%. For the 30% bentonite/10% CEM III mixture, UCS decreased from 1775 to 1800 to 1542 kPa from DOPT to WOPT, K sat from 1.37 × 10 − 9 to 1.93 × 10 − 10 to 9.73 × 10 − 11 m/s, and V s from 3.8 to 3.19 to 2.19%. DOPT was therefore the only condition that violated the hydraulic criterion, despite giving the highest strength, whereas OPT and WOPT met all three criteria. Soil–water characteristic curves (SWCCs) measured by pressure plate up to 1500 kPa were fitted with the Brooks–Corey, Fredlund–Xing and van Genuchten models; all reproduced the data closely (root-mean-square error, RMSE ≤ 0.0035) and the van Genuchten model was marginally best. Water retention increased with moulding water content. 2%WOPT placement of a 31% bentonite/10% CEM III liner is recommended.