Abstract: In an attempt to examine the influence of water content change in expansive soil on canal slope stability, site-monitored data of water content, suction, rainfall, soil temperature and air temperature was analyzed by grey correlation method. The change of water content in strongly expansive soil is mainly affected by temperature, rainfall, evaporation, and suction in order. Grey correlation analysis suggest that rain water infiltrates into strongly expansive soil in a depth of 1.6 m only three days after rainfall, affecting the slope soil in a depth smaller than 6.1 m; it takes 4-7 days for rain water infiltrating into strongly expansive rock in a depth of 1.4 m, with the influence depth within 5.1 m. The long-term monitoring and data analysis offer basis for the safe operation of canals in the South-to-North Water Transfer Project.

Key words: South-to-North Water Transfer Project, canal slope, expansive soil, moisture content, monitoring, grey correlation analysis, infiltration of rainfall