Size Effect on Mechanical Properties of Rock-Like Materials with Three Joints

In order to study the size effect, failure mode and damage evolution process of rock-like materials with three joints, two rock-like materials with different sizes of joints were prepared for uniaxial compression tests. The digital image correlation technique was used to record the change characteristics of the apparent strain field, and an acoustic emission device was applied to record the damage process. The results show that the peak compressive strength of samples with the same joint inclination decreases with the increase of size. The peak compressive strength of samples decreases obviously when the joint inclination ranges from 0°–45° and 75°–90°. When the joint inclination ranges from 45° to 75°, the peak compressive strength of samples decreases insignificantly. With the increase of joint inclination, the peak compressive strength of the sample decreases gradually. It reaches the minimum when the joint inclination angle is 60°, and then the peak compressive strength steadily increased. It is prone to failure when the joint inclination is 60°. According to the crack propagation model, the failure modes of jointed samples can be divided into five failure modes: tension failure, airfoil tension failure, tension-shear mixed failure, shear failure and integral splitting failure. According to the damage curve, the damage evolution process can be divided into inverted L type, spoon type, S type and straight hook type. Large size samples and samples with joint inclination of 0°, 90° and 60° are prone to brittle failure and step damage.