Fracture mechanism of naturally cracked rock around an inverted U-shaped opening in a biaxial compression test

Zhong, Zhibin; Deng, Ran; Lv, Lei; Xiao-min, FU; Yu, Jin

doi:10.1016/j.ijrmms.2018.01.047

Cited by 39 publications

(9 citation statements)

References 30 publications

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“…Their experimental results indicate that initial stress states are of great significance in affecting rockburst tendency and failure degree. Zhong et al performed biaxial compression tests to study the fracture properties of hard and brittle rock specimens containing a U‐shaped opening. Crack initiation, propagation, and coalescence behavior were observed and analyzed in their tests.…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

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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“…At Point A, the axial loading force of the granite specimen was equal to the lateral loading force. Li et al [18] showed that when the stress increases to 78.2% of the peak loading value, critical cracks initiate in the tensile stress concentration zones under uniaxial loading conditions; similar results were also reached by Zhong et al [41]. Based on previous research, the axial loading force at Point B was determined to be 80% of the peak stress under biaxial loading.…”

Section: Axial Load-displacement Curve and Fracture Evolutionmentioning

confidence: 56%

Preliminary Study on High-Energy and Low-Energy Microfracture Event Evolution Characteristics in the Development Process of Rock Failure

Cheng

et al. 2020

Geofluids

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The evolution characteristics of high-energy and low-energy microfracture events play an important role in the brittle failure mechanism of rock and reasonable microseismic (MS) monitoring and acoustic emission (AE) monitoring. The bimodal distribution (BMD) model is commonly used to observe the evolution characteristics of high-energy and low-energy MS events; however, its precise mechanism remains unclear. The evolution characteristics of high-energy and low-energy microfracture events are assessed in this study based on a BMD model. MS monitoring results from the No. 22517 working face of the Dongjiahe Coal Mine are studied, and AE monitoring results of a biaxial compression experiment of a granite specimen are analyzed. High-energy MS events in the No. 22517 working face are found to be generated by an increase in the failure scale of the overlying rock mass upon exiting the insufficient mining stage and entering the sufficient mining stage. The change characteristics of the high-energy AE hits are positively correlated with crack evolution characteristics in the granite specimen and negatively correlated with changes in the Gutenberg-Richter b value. A precise high-energy and low-energy AE hit evolution mechanism is analyzed based on the microscopic structure of the granite specimen. Similarities and differences between high-energy MS events and low-energy AE hits are determined based on these results. Both are found to have bimodal characteristics; an increase in the failure scale is identified as the root cause of the high-energy component. The bimodal distribution of AE hits is far less obvious than that of MS events.

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“…For the actual underground excavation engineering, the above results imply that in order to prevent and control the rock fracturing caused by high compressive stress concentration, the support in the middle of the sidewalls should be strengthened in the elliptical tunnel, and the support at the corner of the square tunnel should be strengthened or apply localized rounding to reduce the stress concentration [ 21 ]. In addition, under the same lateral stress, the tensile stress at the top and bottom of the square opening is larger than that of the elliptical opening, which is more likely to cause the tensile fracture.…”

Section: Results and Analysismentioning

confidence: 99%

Mechanical properties and progressive failure characteristics of sandstone containing elliptical and square openings subjected to biaxial stress

et al. 2021

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Two kinds of common tunnel shapes, i.e. elliptical opening and square opening were selected for biaxial compression tests, and the influences of two kinds of opening shapes on the mechanical properties, failure characteristics and failure modes of sandstone were compared and analyzed. The complex variable theory and mapping functions were used to obtain the analytical stress solution around elliptical and square openings. The results show that the stability of the specimen containing an elliptical opening was better than that of the specimen containing a square opening under the same lateral stress. Compared with the elliptical opening, the local damage was formed earlier in the square opening which might be caused by a higher stress concentration around the square opening. The stress distributions around openings were influenced by the opening shape and lateral stress coefficient. The top and bottom of square opening were more prone to tensile fracture, and the distribution range of tensile was larger than that of elliptical opening. When the opening failed, the intensity of square opening failure was weaker than that of elliptical opening. On the basis of the average frequency value and the rise angle value, the failure mode of specimen containing elliptical or square opening was distinguished. It was found that the mixed tension and shear failure dominated the failure of specimens with different opening shapes, and the number of shear cracks in the specimen containing a square opening was greater than that in the specimen containing an elliptical opening. The above method of judging failure mode by acoustic emission signals was well verified by the CT images of damaged specimens.

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Fracture mechanism of naturally cracked rock around an inverted U-shaped opening in a biaxial compression test

Cited by 39 publications

References 30 publications

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

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

Preliminary Study on High-Energy and Low-Energy Microfracture Event Evolution Characteristics in the Development Process of Rock Failure

Mechanical properties and progressive failure characteristics of sandstone containing elliptical and square openings subjected to biaxial stress

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