Abstract: Expansive soils exhibit pronounced swelling upon wetting and shrinkage upon drying, often triggering slope failures and other geotechnical hazards. Targeted monitoring is therefore essential for effective hazard prevention. This study systematically reviews existing monitoring technologies for expansive-soil slopes, including using GNSS and InSAR for surface displacement monitoring, borehole inclinometers and flexible inclinometers for deep displacement, and techniques for measuring soil water content and matric suction to characterize moisture and hydraulic conditions. Based on this review, a multi-field, three-dimensional automated monitoring system was developed for an expansive-soil slope along an oil and gas pipeline in Guangxi. The system integrates meteorological data, surface and subsurface displacement, moisture and suction parameters, soil pressure, and pipeline strain. Monitoring results indicate that rainfall infiltration is the primary driver of slope deformation and instability, predominantly affecting the shallow 0~3 m soil layer. Slope failure progresses through three stages: slow creep, multi-episode sliding accumulation, and accelerated instability. Soil deformation further compresses the pipeline, causing synchronous increases in pipe stress and strain. Surface displacement acceleration and soil pressure are effective indicators for early warning of impending failure, while variations in water content at different depths can be used to infer potential sliding surfaces within expansive-soil slopes.

Key words: Expansive Soil Slopes, Deformation Monitoring, Moisture Content, Hazard Early Warning