Abstract: Complicated material fabrics are the main factors to control the mechanical characteristics of rock mass; currently the anisotropic problems caused by structural planes are the most hot topics. As a special structure rock mass, the discontinuity and anisotropy of rock mass with columnar joints is very typical. The microstructure can be represented by a second order tensor whose eigenvectors specify the orientation of the axes of material symmetry, which is an effective new method to study structure plane caused anisotropy. Microstructure tensor and loading direction are important parameters for this theory. With projection relation of multiple joint surface between spatial local coordinate system and integral coordinate system considered, microstructure tensor is derived. Using ψ describes the projection of the microstructure tensor on the loading direction. The modified anisotropic failure criterion, which incorporating a microstructure for columnar joints based on Jaeger proposed for failure along the material fabrics, is used to study anisotropy of the multiple joint surface. Meanwhile, we use it to consider the Baihetan hydropower station columnar joint- project and analyze columnar joint anisotropy caused stability problem.

Key words: microstructure tensor, Baihetan hydropower station, columnar joint, failure criterion, anisotropy