In Situ Observation of Rock Spalling in the Deep Tunnels of the China Jinping Underground Laboratory (2400 m Depth)

Feng, Xia‐Ting; Xu, Hong; Qiu, Shili; Li, Shaojun; Yang, Chengxiang; Guo, Haosen; Yuan, Cheng; Gao, Yaohui

doi:10.1007/s00603-017-1387-8

Cited by 136 publications

(31 citation statements)

References 17 publications

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“…e environment of high in situ stress will lead to the storage of high strain energy in rock masses. During excavation, as the initial stress constraint of excavated rock masses on the excavation surface is released, the unloading phenomenon of in situ stress occurs, which causes the initial stress and energy state of the surrounding rock masses to be broken, inducing a series of geological disasters such as damage, microearthquake, rockburst, and deformation in the surrounding rock masses [1][2][3][4]. A large number of field tests and theoretical studies showed that energy release was the essential cause of failure of rock masses [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

Fan

Zheng

et al. 2020

Mathematical Problems in Engineering

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During excavation of deep rock, the release of strain energy plays an important role in geologic hazards caused by excavation. However, in the previous studies, the influence of transient unloading of in situ stress caused by blasting excavation has been ignored, and the blasting excavation of a tunnel is regarded as a single blast process. In this paper, the dynamic adjustment process of strain energy and the energy storage limit of surrounding rocks caused by transient unloading of in situ stress under elastic conditions were firstly analyzed. Then, the brittle-ductile-plastic transition model based on the Hoek–Brown strength criterion was simulated in FLAC3D. Finally, the dynamic release process of strain energy of surrounding rocks caused by multiple unloading disturbances was analyzed during the excavation of 2# Underground Laboratory of Jinping II Hydropower Station employing the newly proposed index, energy release coefficient (ERC). Results show that the strain energy of surrounding rock masses firstly decreases, then increases, next reduces, and finally stabilizes under the transient unloading of in situ stress. In the process of dynamic change of strain energy, when the strain energy exceeds its storage limit, a large amount of strain energy will be released and thus will lead to damage of the surrounding rock masses. Because the cut holes and the first circle of breaking holes are far away from the final excavation boundary, the unloading disturbance to the strain energy of surrounding rock masses is small. Furthermore, the energy release of surrounding rock masses is mainly caused by the unloading of the last circle of breaking holes and perimeter holes, and the closer to the final excavation boundary, the more intense the energy release.

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Section: Introductionmentioning

confidence: 99%

Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

Fan

Zheng

et al. 2020

Mathematical Problems in Engineering

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“…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 . Therefore, it is necessary to gain better insight into the failure characteristics and mechanism response of hard rock around deep tunnels…”

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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“…[1][2][3][4][5][6] Figure 1A,B shows photographs of pre-existing flaws in underground tunnels with different buried depths. 7,8 The stability of rock engineering is significantly affected by flaws in rock masses, because the crack initiation, propagation and coalescence result in the reduced strength and stiffness of rocks and provide potential paths for rock failure. Figure 1C shows a photograph of a failed rock slope owing to the propagation and coalescence of cracks.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on fracture behaviour of three‐flawed sandstone specimens after high‐temperature treatments

Huang

Yang

Dong

2020

Fatigue Fract Eng Mat Struct

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The crack coalescence of rocks significantly affects the stability of rock engineering, and extensive studies have been performed on preflawed rock specimens without thermal treatment. However, the fracturing behaviour of preflawed specimens after thermal treatment has not been investigated comprehensively. In this study, three‐flawed sandstone specimens with different flaw inclinations after high‐temperature treatments were tested under uniaxial compression. Photographic, acoustic emission and digital image correlation techniques were used to investigate the crack initiation, propagation and coalescence behaviour. Experimental results show that the peak strength, elastic modulus and peak strain of the three‐flawed specimens were lower than those of intact specimens and that they gradually recovered with increasing flaw angle. The peak strength and elastic modulus first increased and then decreased, whereas the peak strain increased with temperature. Noncoalescence, indirect coalescence and direct coalescence were three patterns observed between the two adjacent pre‐existing flaws. Finally, the mechanism of high temperature in alteration of the mechanical properties of sandstone was revealed through microobservations.

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In Situ Observation of Rock Spalling in the Deep Tunnels of the China Jinping Underground Laboratory (2400 m Depth)

Cited by 136 publications

References 17 publications

Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

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

Experimental study on fracture behaviour of three‐flawed sandstone specimens after high‐temperature treatments

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