In this study, the uniaxial compression test and PFC ^2D numerical simulation were carried out on the artificial rock specimen with T-shaped prefabricated fractures. The effects of the lengths l₁, l₂ of the main fractures, the length l₃ of the secondary fracture, and the angle β between the secondary fracture and the loading direction on the uniaxial compressive strength and crack evolution law of specimen were studied. The research results show that the change of l₁, l₂ and β has obvious effect on the compressive strength and crack growth of the specimen, but the change of l₃ has little effect on the compressive strength of the specimen. When l₃ = 40 mm and l₁ ≠ l₂, the angle β influences on the crack propagation and failure mode of the specimen.

Dynamic biaxial compression tests and Particle Flow Code numerical simulations of the cement mortar specimens with a single joint were carried out to study the mechanical properties and crack evolution of artificial rock samples with a single joint. The effects of lateral stress 𝜎2, loading rate V , the dip angle β (between the vertical loading direction and the joint) on the biaxial compressive strength 𝜎 _b, and the evolution lawof crackwere investigated. Test results showed that; (1) when both the dip angle β and the loading rate V remained unchanged, the biaxial compressive strength 𝜎 _b increased with the increase in the lateral stress 𝜎2, while 𝜎2 had no obvious effect on the crack evolution law; (2) when both the dip angle β and the lateral stress 𝜎2 were kept unchanged, the loading rate V had an insignificant effect on the biaxial compressive strength 𝜎 _b and the crack evolution law; (3) when both the lateral stress 𝜎2 and the loading rate V were constant, the biaxial compressive strength 𝜎 _b decreased first and then increased with the increase in the dip angle β ; however, the dip angle β did not significantly affect the crack evolution law. The conclusions obtained in this paper are presented for the first time.

In this study, direct shear tests were carried out on cement mortar specimens with singleladder, single-rectangular, and double-rectangular step joints. Consequently, the shear strength, and crack shape of specimens with these through-step joints were analyzed, for understanding the influence of the through-step joint’s shape on the direct shear mechanical properties. The results of the investigation are as follows: (1) Under the same normal stress, any increases in the height ℎ of the step joint causes an initial-increase-decrease in the shear strengths of specimens with single-ladder and double-rectangular step joints, causing a type-Wvariation pattern for the specimens with single-rectangular step joint. More essentially, when normal stress and ℎ are constant, the shear strength of specimens with a single-ladder step joint is the greatest, followed by specimens with a double-rectangular step joint, and then specimens with a single-rectangular step joint is the least. (2) Furthermore, given a smallℎ and low normal stress, specimen with a single-ladder step joint mainly experiences shear failure, whereas specimens with single-rectangular and double-rectangular step joints mainly generate extrusion milling in the step joints.