Anisotropic mechanical behaviors of columnar jointed basalt under compression

Columnar jointed basalt is a typical type of jointed rock mass formed by the combined cutting effect of primary joints and aphanitic fissures and exhibits highly anisotropic mechanical behaviors in terms of strength and deformation modulus. In order to understand the anisotropic mechanical properties of columnar jointed basalt, a series of laboratory tests and numerical simulations were carried out. Firstly, a mixture of water, river sand, and gypsum was prepared to model the columnar jointed basalt. A series of uniaxial compression tests were then conducted according to the different cooling times and prefabricated dip angles (α = 0°–90°). The model test results reveal that the strength and deformation modulus of columnar jointed basalt are obviously affected by the primary joint angles, and the deformation modulus and the peak strength of columnar jointed basalt under uniaxial compression are correlated with the dip angles of primary joints by a U-shaped curve. The deformation modulus and the peak strength reach the minimum when the joint angle is in the range of 60°–75°. A multi-jointed softening constitutive model was the established based on the results of model tests. The 3DEC software was adopted to simulate the uniaxial compression tests. The simulation results are in agreement with the test results, demonstrating the rationality of the numerical method proposed in this paper. Lastly, the triaxial compression tests on columnar joints under different confining pressures were modeled. The modeling results indicate that, with the presence of confining pressure, the similar material exhibits different mechanical properties, such as elastic–plastic and elastic–brittle behaviors, under different primary joint angles. The primary joints are the predominant factor affecting the anisotropy of the similar material. By comparing the normalized indexes, it is found that increasing confining pressure can effectively reduce the effect of columnar joints on the anisotropy of mechanical properties of rock masses.