Baota landslides are one of the four landslides whose volume is more than 1×108 m3 in Three Gorges reservoir area. Baota landslides are in the sandstone and mudstone alternate layers of Jurassic Penglaizhen formation. The clay gouged intercalation

existing much in Baota landslides

is one of the most important reasons of Baota landslides happened. On the basis of geology analysis

using X-ray diffraction （XRD） test

scanning electron microscopy and energy dispersive X-ray test（SEM-EDX）

physical chemistry test and underground water quality analysis test

the composition

the structure

the characters of clay gouged intercalation and its original rock are analyzed contrastively. The reasons of clay gouged intercalation establishment are concluded: the layer structure of sandstone and mudstone alternate layer is the basic reason; the tectonic stress or gravity is the necessary condition; and the long action of underground water is the main reason. The water-rock interaction of clay gouged intercalation establishment is studied on the basis of above conclusion. The study results indicate that hydration

ion exchange

corrosion between underground water and mudstone are promoting each other. These water-rock interactions change the structure

composition and characters of mudstone; then induce the mudstone sludging thoroughly. At last

mudstone is changed into the clay gouged intercalation. Thereby

the establishment mechanism of clay gouged intercalation in Baota landslides is interpreted.