The effect of joint inclination angle on mechanical properties of rock mass studied by model test and DEM simulation

The joint inclination angle is a crucial factor influencing the mechanical behavior of rock masses and greatly affects the stability of rock mass engineering. The article utilizes cement mortar to fabricate jointed rock models with mechanical properties that closely resemble those of real rock formations. The compressive plate speed of the loading test machine is 0.005 mm/s, and the axial static loading rate ranges from 0.5 to 1.0 MPa/s. To investigate the influence of joint inclination angles on the macroscopic mechanical properties of the rock, the study initially employs indoor full-field observation and the non-contact technology known as Digital Image Correlation (DIC). Experiments are conducted on rock specimens with varying joint inclination angles of 30°, 45°, 60°and 90°. Following this, numerical simulations employing the Discrete Element Method (DEM) are conducted to analyze the microfracture process. The model test and numerical simulation results demonstrate good agreement, particularly regarding the failure modes. It is found that the most common failure mode for jointed rock is a composite form of shear and tension. As the joint inclination angle increases, tensile failure becomes more prominent. The Young's modulus EJR/ER and peak strength σJR/σR ratios between jointed and jointless rock vary with the joint inclination angle, exhibiting a "V" shaped curve. A joint inclination angle of 45° results in minimum strength and modulus in the macro mechanical properties. The joint inclination angle has a negligible effect on the rock mass's residual strength, maintaining an approximately constant ratio of 0.14 between residual and peak strength σr/σp.