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Abstract The slip zone of large-scale landslide in the Loess Plateau has been identified as red clay rock of Upper Pleistocene. However，there are few studies about the structural characteristics and formation mechanism of the slip zone. Herein，the fabrics and structural characteristics of clay rocks are introduced based on drilling core analysis，surface survey，X-ray diffraction and scanning electron microscope. Meanwhile，stress-strain test，residual strength test and slip zone creep experiment are also implemented. The formation mechanism of interbedded shear zone in the large-scale landslides is therefore analyzed. The results indicate that the main slip zone consists of rich-developed approximately horizontal shear plane. Plastic deformation and shear deformation break out together with the changes of soil structures in the slip zone. As for the mode of motion，block sliding prevail. It is also found that clay rocks suffer more fissures after evolving into soil of slip zone. The average water absorption velocity reaches 2.7 g/h and the penetrability is promoted. Under such a condition，the water absorption velocity of the standard rock sample in unit period accounts for 1.5 times of original rocks；the specific activity is 0.83. It is better than original rocks in terms of specific surface area and activity. Furthermore，structural changes of original rocks are accompanied by strength attenuation. According to test results，the conhesion of peak strength for original clay rocks with water content of 19.1% is 613 kPa，and the internal friction angle is 26.7°. In Boji mountain，the conhesion and internal friction angle of residual strength of slip zone is 8.79 kPa and 17.2°，respectively；the conhesion and internal friction angle of long-term strength of slip zone is 57.4 kPa and 20.47°，respectively.
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Received: 08 October 2012
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2013, Vol. 32 
