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Abstract:The columnar jointed rock mass is a type of extrusive igneous rock. Correctly understanding the deformation and strength characteristics of columnar jointed rock mass under triaxial stress condition is essential for hydropower station and underground cavern excavation. As it is difficult to obtain the mechanical properties of columnar jointed rock mass by field tests, conventional triaxial compression tests were carried out on simulated columnar jointed rock mass specimens with different dip angles between the direction of principal stress and the column prisms. The changes of Young's modulus and peak compressive strength with dip angle β were obtained. The results indicate that the Young's modulus and peak compressive strength increase with confining pressure for the same group of specimens. However, under the same confining pressure, the curves of Young's modulus and peak strength versus dip angle resemble a "decreasing-order shape", that is, the Young's modulus and peak strength decrease with dip angle β from 0° to 45°, reach minimum values at β = 45°, and then remain relatively constant with the increase of dip angle. Furthermore, four typical failure modes of columnar jointed rock mass specimens under triaxial compression condition are summarized based on the test results. Their failure mechanisms are also discussed.