Abstract: The dip angle of structural plane has great influences on mechanical properties of rock samples. In this study, the rock samples with structural planes of 15°, 30°, 45°, 60° (the structural plane of 0° is along the horizontal direction)and the intact rock samples are prepared. Uniaxial tests and triaxial tests with confining pressures of 100 kPa, 200 kPa and 300 kPa are performed to investigate the influence of dip angle of structural planes on their mechanical and deformation features. Test results demonstrate that: 1) the stress-strain curve exhibits the four typical stages, which are similar to those of rock samples when the dip angle is no more than 30°, but the last phase exhibits the characteristics of softening followed by hardening when the dip angle is equal to 45°or 60°, 2) for all the samples, the contractive volumetric strain is firstly shown, and then the dilative volumetric strain is followed. With the increasing confining pressure, the maximum value of contractive volumetric strain does not change much, but the dilative volumetric strain obviously decreases. With the increase of the dip angle, the contractive volumetric strain slowly increases, and the contractive volumetric strain suddenly changes when the dip angle increases from 30°to 45°. However, the dilative volumetric strain obviously decreases. Finally, the disadvantage of Jaeger’s single structural plane criterion is pointed out, and thus the criterion has been improved. The verification results denote that the improved Jaeger criterion is in good agreement with the experimental results.

Key words: dip angle of structural plane, artificial preparation, rock samples, improved Jaeger criterion