To improve our understanding of the fundamental mechanism of rain-induced landslides in unsaturated expansive soils

artificial rainfall simulation tests were carried out on an 11 m high cut slope in a typical medium-plastic expansive clay in Hubei of China. The slope was well-instrumented with tensiometers

thermal conductivity suction sensors

moisture probes

earth pressure cells

inclinometers

a tipping bucket rain gauge

a vee-notch flow meter and an evaporimeter. Two artificial rainfall events were created during a month of field investigation and monitoring. Monitored results demonstrate: rainfall infiltration leads to a significant increase in pore-water pressure and water content within the top 2 m soil layer

which may result in a reduction of shear strength due to a decrease in effective stress and wetting-induced softening. On the other hand

rainfall infiltration causes a significant increase in total stress ratio (sh/sv)

which may lead to a local passive failure and then trigger a progressive slope failure under a continuous rainfall condition.