Three-dimensional failure behavior and cracking mechanism of rectangular solid sandstone containing a single fissure under triaxial compression

Abstract

In actual rock engineering, fissures play an important role in determining the mechanical parameters of rock mass, whereas it is very difficult to construct fissures in cylindrical specimens. Therefore, the pre-fissured rectangular rock specimens were constructed innovatively. Moreover, a series of triaxial compression experimental results on the failure mechanical behavior of rectangular solid sandstone specimens containing a single fissure were reported. The lateral strain in different directions was monitored and the experimental results show that elastic modulus and axial strain increase non-linearly with confining pressure, and the average Poisson’ s ratio parallel to fissure (μ₂) is larger than that vertical to fissure (μ₃). The cohesion, Hoek-Brown parameters of peak strength show similar trends with that of crack damage threshold to the fissure angle (α), and the parameters of the peak strength are larger than those of crack damage threshold. However, the internal friction angles of the peak strength and crack damage threshold are almost equal. Based on the geometries and properties of cracks, ten typical crack types are identified. Cracks vertical to pre-existing fissures occur in specimens under uniaxial compression, whereas cracks parallel to pre-existing fissures occur under triaxial compression. Finally, X-ray micro-computed tomography (CT) observations are conducted to analyze the internal damage mechanism of sandstone specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of sandstone specimens. This research elucidates the fundamental nature of rock failure under triaxial compression.