Fissure is one of the important characteristics of expansive soils. Shrinkage fissures induced by the wetting-drying cycle effects and the specific inherent fissures distributed in atmospheric influential depth of expansive soil are often confused. In the study of expansive soil slope failure mechanism

the significant impact of the inherent fissure on slope stability is often ignored. In order to study the failure mechanism of expansive soil in middle route of South-to-North Water Transfer Project

a 2.05 km test channel is constructed on the outskirts of Nanyang

Henan province. Geological survey

field observations and sampling tests during excavation

as well as on-site sampling and analysis of slope failure are conducted to study the material composition of expansive soil fissure and the density

water content and strength characteristics of the surrounding soil. Combined with field observations

the relationship between fissures and channel landslide is analyzed. It is shown that there are two types of inherent fissures for the expansive stratum: one is smooth waxy fissure; and the other is filling clay fissure with a certain thickness. The material composition of the fissure surface is slightly different with the adjacent soil

featured by low natural density and high moisture content; and the intensity is much less than the strength of the adjacent soil. Once the formation is consistent with the slope tendency

it would slide along the fissure surface.