Abstract: Slope failure frequently occurred during and after the excavation of phyllite talus at the Wenchuan-Maerkang expressway. Previous research on phyllite talus has mainly considered it as homogeneous soil, while its unique structural features, such as the orientation of the constituted phyllite fragments, is less concerned. Phyllite is a metamorphic rock with foliated structure, and phyllite fragments are characterized with their flattened shape that may cause them to stop accumulating along the slope in a certain orientation. Field investigation shows that the dip direction of the phyllite fragments is usually parallel to or forms only a small angle to the talus slope inclination, which is defined as fragment orientation in this paper. The fragment orientation is considered as an important factor contributing to the slope instability of phyllite talus. Model tests are designed to study the orientation characteristics of the phyllite fragments and its influencing factors by taking the phyllite talus at Wenchuan–Maerkang expressway as examples. Large-scale direct shearing test considering the fragment orientation are consequently performed to explore the effects of fragment orientation on slope stability of phyllite talus. The results show that the slope angle and the content of fine particles in the talus have significant influence over the fragment orientation; when the slope angle is 20°-30°, the orientation is most obvious and rises with the increase of fine particle content; the shearing strength parameters of phyllite talus for slope stability analysis significantly reduce due to the fragment orientation.

Key words: phyllite talus, fragment orientation, experimental study