The effect of cyclic stress amplitude on macro‐meso failure of rock under triaxial confining pressure unloading

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A series of stress‐controlled fatigue–creep interaction loading tests were performed on rock–backfill composite structure (RBCS) samples. The testing results reveal the influence of cement/tailing (c/t) on deformation, energy dissipation, damage evolution, and macro–meso failure patterns. The equivalent lifetime of RBCS is the largest for a sample with smaller stiffness filling, a smaller stiffness filling leads to weaker volumetric expansion. Additionally, strain energy is relatively large for larger stiffness filling, indicating a larger proportion of energy release at failure. A dissipated energy‐based damage evolution model is proposed to describe damage propagation at the entire fatigue–creep process which fits well with the experimental data. Moreover, the macro–meso failure pattern reveals the interactions between surrounding rock and filling material, failure seems to change from tension splitting to shear with increasing c/t. Good agreement was found among the volumetric deformation, energy dissipation, and failure pattern. It is suggested that flexible backfilling is benefit to prevent rock spalling and collapse.

U goodbreak= U_{e} goodbreak+ U_{d},

U goodbreak= \int_{0}^{ε 1} σ_{1} d ε_{1},

U_{e} goodbreak= \frac{1}{2} σ_{1} ε_{1}^{e} goodbreak= \frac{1}{2 E_{u}} σ_{1}^{2},

where

ε_{1}

is the axial strain,

ε_{1}^{e}

is the elastic strain, and

E_{u}

is the unloading elastic modulus. U d reflects the energy consumed in the damage evolution process such as crack initiation, propagation, and merging, and U d is irreversible.…”

Section: Methodsmentioning

confidence: 99%

Section: Energy Conversion Mechanismmentioning

confidence: 99%

On the fracture and energy characteristics of rock–backfill composite structure specimens exposed to fatigue–creep interaction loading

Wang,

Yi,

Long

et al. 2023

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“…Deviatoric stress strain curves with different cyclic stress amplitude, modified from Wang et al 26 (A) CSA = 60 MPa; (B) CSA = 100 MPa; (C) CSA = 130 MPa; and (D) CSA = 160 MPa. [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Mechanical Responses Of Rock With Different Csamentioning

confidence: 99%

“…Following to the previous studies to reveal the effect of cyclic stress amplitude on the rock macro‐meso failure characteristics, 26 this study first demonstrate the stress strain behaviors in order to obtain the strain energy parameters. The deformation curves of the rock samples under fatigue loading and the confining stress unloading conditions are presented in Figure 2.…”

Section: Mechanical Responses Of Rock With Different Csamentioning

confidence: 99%

Investigation of fatigue failure and energy characteristics of rock exposed to complicated stress disturbance paths: Cyclic stress amplitude effect

Wang¹,

Cao²,

Mao

et al. 2023

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To deeply reveal the differences in geomechanical responses of rock during mining exposed to complicated stress disturbance of excavation unloading and cyclic loading conditions, cyclic triaxial fatigue loads with four cyclic stress amplitude (CSA) (60, 100, 130, and 160 MPa) were performed on deeply buried rock. Results show that rock deformation, energy evolution, and failure modes are all influenced by the CSA. Additionally, it is found that all the strain energy increases with increasing CSA during rock failure. Especially, the dissipated energy increases greatly at the confining stress unloading stage (CSUS) than the fatigue loading stage (FLS), indicating the influence of unloading on rock damage accumulation. Moreover, a damage evolution model reflecting a first slow and then quick increase pattern was established using the dissipated energy. Finally, a transition failure mode from the dominant tensile-shear to pure shear is found. It is suggested that much more energy needs to be consumed to induce shear cracks than tensile cracks. K E Y W O R D Scyclic stress amplitude, damage evolution, energy conversion, failure modes, fatigue failure Highlights• Complicated disturbed stress paths were applied to deeply buried rock.• The influences of cyclic stress amplitude on damage and energy dissipation were revealed.• Relatively large energy dissipation occurs at the CSUS compared to the FLS.• A transition failure mode from the dominant tensile-shear to pure shear is found.The geological environments of deeply buried rock mass are characterized with high geo-stress, high geotemperature, high permeability, and strong stress disturbance; those characteristics are distinct from the shallow engineering rock mass. 1,2 Among those features, strong stress disturbance is one of the most common

“…The volumetric strain is calculated using the axial strain (ε a ) and radial strain (ε r ) as ε v = ε a + 2ε r . 31,32 It can be observed that the hysteresis phenomenon occurs at the low-cycle FLS, the pattern of hysteresis loop is influenced by applied dynamic stress amplitude. The axial strain at the failure moment of the RBCS samples is 0.371%, 0.262%, 0.208%, and 0.155%, respectively.…”

Section: Cls Following the Fls Creep Loading Is Applied Tomentioning

confidence: 99%

Alternative fatigue–creep performance of rock‐backfill composite structure material in mine stopes under high static stress: Disturbed amplitude effect

Wang,

Long,

et al. 2023

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This work aims to investigate the dynamic stress amplitude on the mechanical responses of rock‐backfill composite structure material under alternative low‐cycle fatigue loading and creep loading tests. Results show that deformation, damage propagation, and failure pattern are all impacted by the stress amplitude, and volumetric deformation is the largest for a sample subjected to strong stress disturbance. The equivalent lifetime decreases with the increase of disturbed amplitude. A notable positive interaction between the fatigue damage and time‐dependent damage is found, and they promote each other. Additionally, a novel damage evolution model is proposed by the irreversible radial strain, and the model matches well with the testing data. Moreover, post‐test computed tomography imaging reveals that cracks at rock‐backfill interfaces are relatively easy to be stimulated under low stress disturbance, and it is suggested that tension‐splitting failure is more likely to occur within the surrounding rock, and shear failure seems to occur within the cemented tailings backfill for all the tested samples.