Abstract
Abstract Shear instability behavior is typical failure mode of rock mass in civil and mining engineering. Many attempts have been performed for rock joints or nonpersistent rock bridge under static shear conditions, yet the shear failure of rock mass subjected to cyclic or fatigue shear conditions is not well understood. Multilevel cyclic shear (MLCS) loading experiments were carried out on freeze-thawed hornfels to reveal the fracture and energy evolution characteristics using a self-special designed rock dynamic shear testing apparatus. The effect of the preexisting natural fracture on rock shear strength, deformation, energy dissipation, and shear failure pattern were experimentally investigated. The testing results show that aperture of open-mode fractures increases quickly, and this kind of natural fracture contributed a lot to rock failure. The evolution of stress hysteresis loop and its pattern are impacted by natural fracture, and it determines the damage accumulation. In addition, a damage evolution model was proposed to describe the damage evolution defined by the dissipated energy; the model can well describe the two-stage damage propagation for each cyclic stage and the entire cyclic loading process. Good agreement was found among the irreversible strain, energy dissipation, and failure morphology that are influenced by the preexisting natural fractures. It is suggested that the rock dynamic shear failure behaviors are rock structural dependent; the disturbed stress alters the energy dissipation and release characteristics.
Highlights
Deformation and damage resulting from shearing usually occur during the construction and development of rock structures [1,2,3]
Accurate determination of rock shear strength by laboratory direct shear test on small scaled specimens is the premise of comprehensive understanding of large scale in situ behaviors of rock mass, which has been studied by many scholars [7, 8]
Laboratory direct shear tests are concentrated in two kinds of works: one kind is for rock joints [9,10,11], and the other kind is for rock bridge [12,13,14]
Summary
Deformation and damage resulting from shearing usually occur during the construction and development of rock structures [1,2,3]. Rock mass from a tunnel or cavern may undergo deep fracturing caused by stress disturbance during construction operation [17] This is to say, the dynamic shear failure of engineering rock mass is closed to the real stress state in civil and mining engineering. No study seems to have investigated cyclic or fatigue shear mechanical behaviors of rock joints or rock bridge It remains mostly unknown what the fracturing characteristics of rock mass exposed to cyclic shear stress and how the shear failure morphology would depend on cyclic loading conditions. To fill this knowledge gap, a rock dynamic shear testing apparatus characterized with varied-frequency and variedamplitude performance was developed. A fatigue damage evolution model defined using the dissipated energy was proposed to describe the two-stage damage evolution of hornfels
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