Review of unloading tests of dynamic rock failure in compression

Wang, Hongyu; Dyskin, Arcady; Dight, Phil; Pasternak, Elena; Hsieh, Ariel

doi:10.1016/j.engfracmech.2018.12.022

Cited by 29 publications

(13 citation statements)

References 43 publications

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“…ese microcracks mainly resulted from the triaxial unloading test, indicating that the triaxial unloading condition could change the stress conditions of sandstone samples and cause damage if the stress reached a critical strength limit. is is consistent with other studies such as Dyskin and Germanovich [3] and Wang et al [4]. It should be noted that these microcracks were caused by triaxial unloading condition when the sandstone samples were less than 75 MPa in this study.…”

Section: Microcrackssupporting

confidence: 93%

“…During the excavation of deep tunnels under high-stress conditions, the stress concentration near the excavation surface reduces the radial stress component and increases the tangential stress component, leading to nonviolent or violent surface failure, i.e., spalling and strain burst, respectively [1][2][3][4]. ese two significant geohazards could affect the safety of personnel and infrastructure in excavations and deep underground mines.…”

Section: Introductionmentioning

confidence: 99%

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Microscopic Characteristics of Fractured Sandstone after Cyclic Freezing‐Thawing and Triaxial Unloading Tests

Shen

Zhu

2019

Advances in Civil Engineering

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e understanding of tunneling rock failure characteristics under unloading conditions in the cold region is critical for the proper design of rock tunneling support and mining safety operation. Given this understanding is currently limited, this study aimed to investigate the characteristics of fractured sandstone samples in the microscale after cyclic freezing-thawing and triaxial unloading tests. e samples were first subjected to different cycles of freezing and thawing, followed by the triaxial unloading test and scanning electron microscopy imaging. e peak strength and damage dilatancy stress were measured from the stress-strain curves. e microcrack characteristics (number, length, and width) were obtained through the image analysis. e results show that the decrease in peak strength and damage dilatancy stress was more significant by the first 20 freezing-thawing cycles when the pore pressure gradient is maximum compared to the later freezing-thawing cycles. e mechanical properties also significantly deteriorated when the severe freezing-thawing treatments were performed. e fracture section mainly had the morphology of honeycomb-like microstructure, stripped microstructure, and flocculent microstructure. e cracking extent was mainly influenced by the freezing-thawing rather than the triaxial unloading test, but the azimuthal angle of microcracks was significantly altered by the triaxial unloading. To properly design rock tunneling support and safe operation of mining in the cold region, both impact of cyclic freezing-thawing and the excavation operation direction should be considered.

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Section: Microcrackssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Microscopic Characteristics of Fractured Sandstone after Cyclic Freezing‐Thawing and Triaxial Unloading Tests

Shen

Zhu

2019

Advances in Civil Engineering

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“…Therefore, a large number of tunnels and chambers will be constructed and excavated in deep rockmass to meet the needs of underground engineering projects (Dammyr et al;Huang et al; Kang et al). Compared to the stress states of shallow buried depth, the mechanical characteristics of hard and brittle rocks at greater depth have been acknowledged to behave quite differently because of their complex stress states . Because a large amount of energy is stored in the hard rockmass, the excavation unloading of deep tunnels and chambers will lead to stress redistribution and concentration, which create favorable conditions for rock fracturing and instability .…”

Section: Introductionmentioning

confidence: 99%

“…Compared to the stress states of shallow buried depth, the mechanical characteristics of hard and brittle rocks at greater depth have been acknowledged to behave quite differently because of their complex stress states . Because a large amount of energy is stored in the hard rockmass, the excavation unloading of deep tunnels and chambers will lead to stress redistribution and concentration, which create favorable conditions for rock fracturing and instability . In situ measurements have shown extremely unconventional failure phenomena in deep mining and tunneling engineering such as slabbing, zonal disintegration, and rockburst, which are of great threats to safe and efficient underground construction and activity .…”

Section: Introductionmentioning

confidence: 99%

“…Much effort has been dedicated to understanding the instability and failure of surrounding rock of deep roadway after unloading . The mechanical response of rock around deep tunnels subjected to an unloading and loading mode should be quite different because of the disparate stress path between them . When an underground opening is excavated, the accumulated energy in the hard rock will be released and deformation and fracture will occur near excavation boundaries.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of fractures of a hard rock specimen via unloading of central hole with different sectional shapes

Fan

Chen

et al. 2019

Energy Science & Engineering

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Hard rock failure and rockburst hazards under high in situ stresses have been the subject of deep rock mechanics and engineering. Previous investigations employed cubic rock specimens with a central hole for simulation of rock fracturing around deep tunnels at a laboratory scale, while the failure characteristics and crack evolution behavior around different shapes of holes induced by excavation unloading response have been barely considered. A commercially combined finite‐discrete element method (combined FEM/DEM) was used to investigate the failure characteristics and crack propagation process of typical hard rock specimens (marble) via the unloading of central hole with different shapes. Rock heterogeneity was also considered in the model in combination with the engineering reality. The combined FEM/DEM approach was first validated by simulating uniaxial compression and Brazilian tests. Then, the parametrical analysis was conducted in detail on the basis of five different sectional shapes of central holes, including a circle, ellipse, U‐shape, trapezoid, and cube, and two lateral pressure coefficients. Analysis of crack propagation paths, released strain energy, displacement, and average velocity distribution of the monitoring points around the central hole suggests that the failure degree and destruction intensity are strongly related to the sectional shape and lateral pressure coefficients. Hard and brittle rock failure induced by the excavation unloading effect can be classified as stable failure (slabbing failure) and unstable failure (strain rockburst). The cubic, trapezoidal, and U‐shaped holes within the specimen are the most likely to induce unstable failure, while stable failure is the dominant failure pattern around circular and elliptical holes. The lateral pressure coefficient λ was also found to affect failure position and intensity (only for the axisymmetric section) around the central hole. The influence of rock heterogeneity on failure intensity and range around the central hole within the specimen was also discussed. This study emphasizes the importance and necessity of the excavation unloading effect when evaluating surrounding rock failure around deep tunnels.

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Analysis and control of the mechanism of coal pillar sloughing in the shallow buried thick coal seam

Zhang

Yang

et al. 2022

Energy Science & Engineering

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In northern Shaanxi province, the coal seam deposit conditions are generally characterized by large thickness and shallow depth of burial, the phenomenon of coal pillar sloughing is serious in the process of working face retrieval, which brings great potential danger to mine safety production. In this paper, by monitoring the stress and damage of the coal pillar in the field section, the stress changes and damage degree of the working face in different mine stages are determined. A new mechanical model of coal pillar in a thick coal seam is constructed and the stress changes and structural breakage law of each section are obtained, the stress transfers mechanism of overburden structure and the stress damage to coal pillar during the mining process of upper and lower section comprehensive mining working face is analyzed. The stress, microscopic damage, and the degree of sloughing in the coal pillar were significantly reduced by monitoring through the top plate hydraulic cracking pressure relief control program. The results of the study show that the extent of sloughing coal pillar and internal damage is closely related to the length of key block B of the masonry beam formed by the overlying rock layer and the position of the break line, by changing the orientation of the overlying masonry beam rock layer and the position and length of the tendency to break line, the sloughing coal pillar is effectively controlled and its stress and damage are reduced. We have achieved good results in control of the sloughing in the Hanjiawan coal mine and similar mines in northern Shaanxi.

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Review of unloading tests of dynamic rock failure in compression

Cited by 29 publications

References 43 publications

Microscopic Characteristics of Fractured Sandstone after Cyclic Freezing‐Thawing and Triaxial Unloading Tests

Microscopic Characteristics of Fractured Sandstone after Cyclic Freezing‐Thawing and Triaxial Unloading Tests

Analysis of fractures of a hard rock specimen via unloading of central hole with different sectional shapes

Analysis and control of the mechanism of coal pillar sloughing in the shallow buried thick coal seam

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