Study on True Triaxial Mechanical Characteristics with Hole Defects of Sandstone

In order to deeply understanding of the mechanical behavior and failure characteristics of deep flawed rocks, the sandstone materials were processed with different diameter and number of holes into cube samples as 50 mm×50 mm×100 mm. The GCTS RTX-3000 rock triaxial instrument was used to carry out true triaxial test on the hole-defective sandstone specimens. The lateral stress remained unchanged after being loaded to a certain value, and the maximum principal stress continued to be loaded until the specimen failed. It explored whether the Mogi-Coulomb strength criterion can be used to describe the strength characteristics of rock samples with defects. The test results show that the existence of holes causes the mechanical parameters of the specimen to deteriorate significantly, and the test piece will enter the plastic yield stage in advance, and the peak strength drops significantly. In the initial stage of loading, the growth rate of lateral strain increases with the increase of the aperture and the number of holes, and then tends to be flat. However, the expansion of the specimen is not obvious under the double holes and three holes. The failure of the specimen is mainly shear failure. The crack of the single hole extends through the entire specimen in a large “X” shape, and in “N” shaped cracks of double holes. But the stress concentration area forms a stress shielding area around the holes under the three holes, and the hole effect occurs.