Geotechnical characteristics and mitigation strategies for loess subgrades in the Ili Valley, China

Loess is a distinctive soil widely distributed along the critical corridors of the Belt and Road Initiative, critically influencing the stability and sustainability of infrastructure. Unlike typical Loess Plateau deposits, loess in the Ili Valley forms under a unique combination of semi-arid climate, seasonal freeze-thaw cycles, salinisation and tectonic activity. These environmental conditions lead to complex subgrade failures characterised by coupled hazards including collapsibility, frost heave, thaw settlement, salt expansion and dissolution. Current research remains fragmented, addressing single hazards or transferring mitigation approaches from other regions, leaving a gap in the understanding of multi-field interactions and regionally adapted countermeasures. This review summarises recent advances in geotechnical characteristics and mitigation strategies for Ili Valley loess subgrades. It outlines the genesis, composition and multi-scale structure of the loess, emphasising its high-water sensitivity, salinity and freeze-thaw susceptibility. The mechanisms of long-term performance degradation under coupled water-temperature-salt-stress interactions are analysed, highlighting limitations in existing models. Mitigation techniques are critically evaluated for their long-term effectiveness, ecological compatibility and techno-economic feasibility in the local context. Finally, future research directions are proposed. This review provides a theoretical reference and a technical framework for engineering safety and hazard mitigation in the Ili Valley and similar geologically complex regions.