To study the influence of rainfall infiltration on suction, water content and deformation of loess subgrade slopes, artificial rainfall simulation tests were conducted for four times on a 9 m high loess filled subgrade slope of Pingliang-Dingxi Expressway in Gansu Province, China, and the total in-situ monitoring continued for a month. Monitored results show that rainfall infiltration leads to obvious increase in soil moisture and decrease in soil suction within the top 1m soil layer, which results in a reduction of effective stress and shear strength. Meanwhile, the development of gullies on slope surface results in larger infiltration of rainfall and as a result a further decrease in shear strength. The maximum rain-induced collapse deformation occurred at the toe of the slope where the compaction degree is the lowest, which may lead to a local subsidence and trigger a slide slope failure in the condition of continuance rainfall. In consideration of controlling collapse deformation, reducing rainfall infiltration and the loss of shear strength of soil, it seems quite important to increase compaction degree of loess subgrade slopes.
