Abstract: In order to study microstructure and mechanical properties of broken phyllite, the typical broken phyllite along the Wenchuan-Maerkang expressway was taken as the research object. X-ray powder diffraction, thin slice identification, uniaxial and triaxial compression tests were carried out. The results show that:1) The microstructure and mineral components are very complex. Most of the rocks have obvious brittle, plastic deformations and fractures with poor structural stability. 2) Significant anisotropy of broken phyllite was observed. Some mechanical parameters increased after the first decrease, such as the elastic modulus, compressive strength, cohesion and friction angle. These mechanical parameters showed a V-shape when the angle varied from 0° to 90°. 3) The failure modes of broken phyllite are closely related to angles and the confining pressure, which can be summed up in five types:tensile splitting along structural plane, shearing slip failure structural plane, Y type tensile-shear compound failure, compound shear failure across and along structural plane, and shear failure cross structural plane. 4) With the increasing of confining pressure, the strength, deformation parameters and failure modes of rock samples gradually weakened. 5) The combination of the maximum principal stress and the structural plane controls the failure mode and mechanism of rock, and it is the fundamental reason for the anisotropy of broken phyllite.

Key words: broken phyllite, microstructure, mechanical properties, anisotropy, failure modes