Photoelastic experiments on failure characteristics of fractured rock with different sizes

In order to fully study the effect of specimen size and crack dip angle on the failure mechanism of fractured rock, uniaxial compression tests on rocks with different specimen sizes and crack dip angles are performed. The whole stress and strain of specimen surface is calculated based on the optical-stress law. The effect of sizes and crack dip angles on rock strength and failure modes is analyzed, and the extension mechanism of fissures in the fractured rock is studied. The test results show that the uniaxial compression stress-strain curve of fractured rock can be divided into the elastic stage, plastic stage and post-peak softening stage, however, the residual stage is not obvious. The elastic modulus of fractured rock during pre-peak stage increases with the increase of height-width ratio of specimens and decreases with the increase of crack dip angles. The uniaxial compressive strength decreases with the increase of height-width ratio of specimens. The post-peak softening characteristics of fractured rock are influenced by crack dip angles and specimen sizes. The greater the crack dip angle and height-width ratio, the more sudden the failure, the more obvious the brittleness. The maximum strain and stress distribution is in the center of the pre-crack, and damage firstly occurs in the pre-crack. With the increase of stress level, the position of the maximum strain and stress propagates to the ends of the crack and extends to the direction of crack parallel to the axial load. The results may provide a theoretical basis for the establishment of constitutive model for fractured rock and the stability analysis of joint rock mass.