Behaviour of Weak Shales in Underground Environments

Martin, C. Derek; Giger, Silvio B.; Lanyon, G. W.

doi:10.1007/s00603-015-0860-5

Cited by 13 publications

(4 citation statements)

References 12 publications

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“…2 As the parent rock of shale gas, shale is a kind of sedimentary rock formed by clay under the action of pressure and temperature, and there are many thin or flake beddings. 3 Due to the low cementation strength of the bedding plane, the physical and mechanical properties of the layered rock show great differences in the direction parallel to and perpendicular to the bedding plane. 4 Affected by the bedding plane, the mechanical properties, strength characteristics and fracture mode of shale formation show obvious anisotropy.…”

Section: Introductionmentioning

confidence: 99%

“…It is estimated that China’s recoverable shale gas reserves are about 25 × 10 12 m 3 , ranking first in the world . As the parent rock of shale gas, shale is a kind of sedimentary rock formed by clay under the action of pressure and temperature, and there are many thin or flake beddings . Due to the low cementation strength of the bedding plane, the physical and mechanical properties of the layered rock show great differences in the direction parallel to and perpendicular to the bedding plane .…”

Section: Introductionmentioning

confidence: 99%

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Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Wei,

Yang,

Zhai

et al. 2024

Energy Fuels

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In order to study the damage evolution and splitting failure characteristics of shale with different bedding orientations under dynamic pulse load, different impact velocities (40, 50, 60, 70 m/s) are selected to carry out dynamic pulse load on D-type and S-type shale samples. Ultrasonic testing, Brazilian splitting test [combined with digital image correlation technology and acoustic emission (AE) monitoring], and nuclear magnetic resonance are carried out on shale samples before and after impact. The results show that the P-wave velocity damage coefficient and splitting mechanic parameters of D-type shale show exponential attenuation, while those of S-type shale show linear attenuation. With the increase of impact velocity, the time-domain spectra of D-type and S-type shale show different degrees of waveform distortion. The frequency-domain spectra present a change characteristic of "high-frequency decrease, low-frequency increase", the total energy of energy spectra decreases, and the main frequency band shifts from medium frequency sub-band (fourth to sixth) to low frequency sub-band (especially first). The AE characteristics of D-type shale are peak distribution with obvious brittle fracture characteristics, while S-type shale is uniformly distributed with progressive failure characteristics. The horizontal strain cloud map shows a band-like stress concentration distribution. Before and after impact, the total porosity of D-type shale decreases, while that of S-type shale increases. The fractal dimension of mesopores generally increases, while the fractal dimension of macropores remained basically unchanged. The existence of the bedding surface is the main reason for the difference in fracture mechanism of different types of shale, and the weakening of the bedding surface caused by impact load is an important factor that complicates the complexity of this difference.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Wei,

Yang,

Zhai

et al. 2024

Energy Fuels

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“…The development of deep underground engineering often leads to major disasters, such as roof caving and collapse, which pose a serious threat to underground workers. Shale has the characteristics of bedding and easy degradation in water, which can easily cause engineering problems (Martin et al [1]). Thus, studies on the influence of water content on the acousto-mechanical properties and failure behaviors of shale during experiments have important theoretical and practical significance for the stability evaluation of underground engineering.…”

Section: Introductionmentioning

confidence: 99%

“…In this study, uniaxial and triaxial compression tests combined with AE technology were carried out on shale specimens with three moisture states (natural, immersion in water for 12 h and saturation) to comprehensively study the effects of water content and confining pressure on the shale's acousto-mechanical properties. The innovation of this study is manifested in the following two aspects: (1) The acoustic emission characteristics of the failure process of water-bearing shale were studied by combining acoustic emission technology and time-reversed Omori's law. (2) The microscopic mechanism of water softening failure of shale is summarized and revealed.…”

Section: Introductionmentioning

confidence: 99%

Influences of Water Content on Acousto-Mechanical Properties and Failure Behaviors of Triaxially Compressed Shale

2023

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Due to the extreme water sensitivity of shale, the excavation of shale underground engineering is prone to major disaster accidents such as roof falls and collapses. However, current investigations have failed to fully explain the mechanisms by which water content affects shale damage behaviors. In this study, the acousto-mechanical properties and failure behaviors of laminated shale under different confining pressures σ3 are investigated with the aid of AE monitoring for three different water content states. The results show that the shale strength decreases with the increase of the water content, but it increases as the confining pressure σ3 increases. For the shale, the change in the wetting angle and the distance between the centroids of the two adjacent particles inside the bedding plane is more prominent than the surrounding shale matrix, and the swelling pressure is generated among the clay minerals, which are the two main mechanisms for the bedding-participating failure and the shale softening after immersion. Moreover, with the increase of the water content and σ3, the damage mode of shale specimens gradually changes from tension damage to shear damage. Controlled by bedding, shale failure shows significant suddenness without clear acoustical precursors. This study provides experimental and theoretical bases for the stability analysis of shale underground engineering.

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Calibration Method and Material Constants of an Anisotropic, Linearly Elastic and Perfectly Plastic Mohr–Coulomb Constitutive Model for Opalinus Clay

Nordas,

Brauchart,

Anthi

et al. 2023

Rock Mech Rock Eng

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Nagra, the cooperative for developing and implementing a long-term radioactive waste depository in Switzerland, identified Opalinus Clay as the most suitable host rock for deep geological containment. This paper deals with those features of Opalinus Clay that are important for the design and construction of the underground structures. Consolidated drained (CD) and consolidated undrained (CU) triaxial compression tests on specimens from deep boreholes revealed that Opalinus Clay exhibits pronounced stiffness and strength anisotropy, dependency of stiffness on the initial confining pressure, slightly non-linear pre-failure stress–strain behaviour, and a drop in axial resistance after a certain amount of shearing. Within the scope of establishing a rigorous—yet practical—design approach for the repository tunnels and caverns, the simplest possible constitutive model capable of reproducing the main aspects of the Opalinus Clay behaviour is adopted. The non-associated linear elastic and perfectly plastic MC model is chosen as a starting point, on account of its wide use in tunnel engineering practice, its simplicity, and the clear physical meaning of its parameters. This paper presents a systematic and robust calibration method for an extended version of this model, which considers the pronounced strength and stiffness anisotropy of Opalinus Clay. The paper additionally provides the full suite of the equations that describe the model behaviour under triaxial CU or CD testing conditions and for any bedding orientation relative to the specimen axis. The equations are employed to determine ranges of material constants for two varieties of Opalinus Clay, based upon the results of 73 CU and CD tests. A thorough comparison between the model predictions and the experimental response is conducted, to demonstrate the versatility and limitations of the constitutive model and of the proposed calibration approach.

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Behaviour of Weak Shales in Underground Environments

Cited by 13 publications

References 12 publications

Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Damage Evolution and Splitting Failure Mechanism of Layered Rock under Dynamic Pulse Load

Influences of Water Content on Acousto-Mechanical Properties and Failure Behaviors of Triaxially Compressed Shale

Calibration Method and Material Constants of an Anisotropic, Linearly Elastic and Perfectly Plastic Mohr–Coulomb Constitutive Model for Opalinus Clay

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