Abstract: The occurrence environment of intermittent columnar jointed basalts in water conservancy and hydropower projects in the mountainous regions of southwest China is complex. Indoor mechanical testing is a valuable method for investigating the failure pattern and degradation mechanism of columnar jointed basalts. With the help of 3D printing technology, MTS uniaxial compression test and macro camera photography, the failure pattern of columnar jointed basalts is extensively investigated, and the anisotropic effect of columnar jointed basalts is discussed and quantitatively analyzed. The research results show that the failure pattern of simulated columnar jointed basalt samples varies significantly due to the influence of the inclination angle of the cylinder. In line with the failure phenomena of columnar jointed basalts that are exposed in underground excavation engineering of dam area, three typical failure patterns of physical models of columnar jointed rock masses are presented. Axial splitting failure along the columnar joint network, shear-slide failure along the columnar joint surface, tensile-shear failure through the columnar joint network are observed. The variation curves of the peak strength and deformation modulus of simulated columnar jointed basalt samples with the change of column inclination angle present the “shoulder shape” anisotropy. The concept of strength and modulus anisotropy ratio is introduced, and the anisotropy grade of simulated columnar jointed basalt samples under different inclined angles is given. The research results have certain reference value for the analysis of deformation and failure pattern and anisotropic characteristics of actual engineering rock masses.

Key words: basalt, failure pattern, deformation and failure, anisotropy, columnar joint