Abstract
This paper aims to investigate the strength and failure mechanism of fractured rock under seepage pressure. For this purpose, precracked sandstone specimens were prepared with different fissure angles, and a seepage pressure loading device was created. Together with the acoustic emission (AE) system, the loading device was adopted to perform uniaxial compression tests with or without seepage pressure. The main results are as follows. Combined with axial stress-strain curves, photographic monitoring results and the output of AE counts and rock failure process can be generally divided into four stages: microcrack closure, elastic deformation, crack growth and propagation, and final failure. The seepage pressure had a significant effect on the mechanical properties of the specimens: the specimens under seepage pressure lagged far behind those without seepage pressure in peak strength but maintained a comfortable lead in peak strain. Under seepage pressure, the typical failure features of the specimens varied with the fissure angles: the specimens with small fissure angles (i.e., [0°,30°]) mainly underwent tensile failure; those with medium fissure angles (i.e., [30°,60°]) suffered from shear failure; and those with large fissure angles (i.e., [60°,75°]) were prone to tensile-shear failure.
Highlights
As a complex natural medium, the rock mass acquires various defects under tectonic actions, including microcracks, pores, and joints. ese defects directly bear on the physical and mechanical properties of the rock mass
Much research has been done on the crack propagation mechanism of precracked rock under uniaxial compression. e previous studies have shown that two kinds of cracks, e.g., wing cracks and secondary cracks, may initiate from the tip of a single open crack under uniaxial compression [1,2,3,4]
Wing cracks are induced by the tensile force, while secondary cracks are the result of shear force
Summary
As a complex natural medium, the rock mass acquires various defects under tectonic actions, including microcracks, pores, and joints. ese defects directly bear on the physical and mechanical properties of the rock mass. Bobet and Einstein [8] conducted uniaxial compressive tests on gypsum specimens with parallel cracks and compared the initiation, propagation, and coalescence of wing cracks and secondary cracks with open or closed fissure. On this basis, the scholar put forward eight different crack coalescence modes and disclosed the strength impact of these modes. Li et al [19] adopted a numerical program, Realistic Failure Process Analysis 2-D (RFPA2D) to simulate the crack initiation, propagation, and coalescence of reinforced specimens under true triaxial compression and hydraulic pressure and studied the effects of the confining stress ratio, gravel sizes, and gravel volume content on the mechanical properties of the specimens. Based on the experimental results and the AE characteristics during the loading process, emphasis on the crack types and crack coalescence process with different fissure angles under seepage pressure was made. e ultimate goal is to reveal the relationship between crack coalescence process and the deformation failure behavior of sandstone containing a hole and fissure under uniaxial compression
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