Mechanical Behavior of Brittle Rock-Like Specimens with Pre-existing Fissures Under Uniaxial Loading: Experimental Studies and Particle Mechanics Approach

Joints and fissures with similar orientation or characteristics are common in natural rocks; the inclination and density of the fissures affect the mechanical properties and failure mechanism of the rock mass. However, the strength, crack coalescence pattern, and failure mode of rock specimens containing multi-fissures have not been studied comprehensively. In this paper, combining similar material testing and discrete element numerical method (PFC2D), the peak strength and failure characteristics of rock-like materials with multi-fissures are explored. Rock-like specimens were made of cement and sand and pre-existing fissures created by inserting steel shims into cement mortar paste and removing them during curing. The peak strength of multi-fissure specimens depends on the fissure angle alpha (which is measured counterclockwise from horizontal) and fissure number (N (f)). Under uniaxial compressional loading, the peak strength increased with increasing alpha. The material strength was lowest for alpha = 25A degrees, and highest for alpha = 90A degrees. The influence of N (f) on the peak strength depended on alpha. For alpha = 25A degrees and 45A degrees, N (f) had a strong effect on the peak strength, while for higher alpha values, especially for the 90A degrees sample, there were no obvious changes in peak strength with different N (f). Under uniaxial compression, the coalescence modes between the fissures can be classified into three categories: S-mode, T-mode, and M-mode. Moreover, the failure mode can be classified into four categories: mixed failure, shear failure, stepped path failure, and intact failure. The failure mode of the specimen depends on alpha and N (f). The peak strength and failure modes in the numerically simulated and experimental results are in good agreement.