A Novel Mogi Type True Triaxial Testing Apparatus and Its Use to Obtain Complete Stress–Strain Curves of Hard Rocks

Feng, Xia‐Ting; Zhang, Xiwei; Kong, Rui; Wang, G.

doi:10.1007/s00603-015-0875-y

Cited by 199 publications

(42 citation statements)

References 22 publications

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“…We have already used the same cores to study the influence of the intermediate principal stress (σ 2 ) on the permeability evolution during true triaxial compression [41]. Although this paper emphasizes the effect of confining pressure (P c ) on the strain-permeability behavior of mudstone, which can be tested by a conventional triaxial apparatus with a cylindrical specimen, the true triaxial apparatus for rocks [41][42][43][44][45] at the Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, which can exert three stresses independently, was still employed in this study because the specimen usually failed with a relatively flat fault parallel to σ 2 [42,[46][47][48]; the flow in the σ 2 direction can still be regarded as a one-dimensional flow. In contrast, the fault of the specimen in the CTC is not only very rough but also oblique to the flow direction [40,49] and the fluid flow inside the specimen near or after failure cannot be approximated as a one-dimensional flow; therefore, the cores in this study were also processed into cuboid specimens of 5 cm square by 10 cm long ( Figure 1) and the permeability in the σ 2 direction was monitored during deviatoric loading.…”

Section: Specimen Apparatus and Experimental Proceduresmentioning

confidence: 99%

Investigation of the Effect of Confining Pressure on the Mechanics-Permeability Behavior of Mudstone under Triaxial Compression

et al. 2019

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Injecting CO 2 into a reservoir disturbs the geostress field, which leads to variations in the permeability of caprock and affects its sealing performance. In this paper, the evolution characteristics of the permeability of Yingcheng mudstone were experimentally studied during deviatoric compression under different confining pressures. As the confining pressure increased, the strength of the mudstone increased bilinearly, the angle between the fault and the maximum principle stress increased, and the fault became flatter. During compression, the permeability of mudstone first decreased and then increased and the turning point of the permeability was between the onset of dilatancy and the turning point of volumetric strain; when the fault formed, the permeability increased sharply and the fault-induced increment was reduced exponentially with increasing confining pressure. In addition, the mudstone transformed to the ductile failure mode when the effective confining pressure was greater than 35 MPa, which means that the permeability did not jump within a small strain. Finally, a practical strain-based model of permeability evolution that separately considers compaction and dilatancy was proposed, and the predicted permeability values were in good agreement with the experimental results. This study revealed the effect of confining pressure on permeability evolution during compression and can help evaluate the sealing ability of mudstone caprock.

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Section: Specimen Apparatus and Experimental Proceduresmentioning

confidence: 99%

Investigation of the Effect of Confining Pressure on the Mechanics-Permeability Behavior of Mudstone under Triaxial Compression

et al. 2019

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“…Although many true triaxial compressive tests have demonstrated that the strength of rocks can be increased by increasing σ 2 , the strength of this mudstone was not affected, which is illustrated by the 6% relative difference between the maximum and minimum strengths. The effect may be weak and unobservable because of the dispersion of the results.…”

Section: Resultsmentioning

confidence: 99%

“…[21][22][23][24] The intermediate principal stress σ 2 has been shown to have a significant effect on the strength and deformation properties of rocks, and the ductility of rocks can be decreased by increasing σ 2 . [25][26][27] However, other than Takahashi et al, 28 Al-Harthy et al, 29 and Li, 11 who studied the permeability characteristics of sandstone in true triaxial stress environments, few studies have investigated the influence of σ 2 on the permeability of mudstone. In this work, the permeability of mudstone in a complete stress-strain process is tested under different σ 2 conditions using a true triaxial testing system, and the impact of σ 2 on the permeability evolution characteristics of mudstone during compression is discussed.…”

Section: Introductionmentioning

confidence: 99%

Effect of the intermediate principal stress on the evolution of mudstone permeability under true triaxial compression

et al. 2017

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The changes in the permeability of mudstone specimens under compression with different intermediate principal stresses (σ2) were tested using a true triaxial testing system. The confining pressure and pore pressure were set based on the caprock conditions in a CO2 geological storage project. The measured permeability initially increased and then decreased before the failure of the specimen and reached a peak in the form of a sudden increase during the formation of the fault. The permeability during compression decreased with increasing σ2. However, the higher σ2 caused the ductility of the mudstone to decrease significantly and led to the formation of a fault parallel to the σ2 direction. The increase in permeability during the formation of the fault was notably suppressed by the increase in the confining pressure and decreased with increasing flatness of the fault; the flatness of the fault increased with increasing σ2. Moreover, an empirical function that considers the compressive and dilatant strains was proposed to predict the permeability before the failure of the specimen, and the parameters of this function are only slightly affected by σ2. The results of this study reveal the effect of σ2 on the variation of the permeability of mudstone and help better assess the risk of caprock leakage in injection projects. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

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“…Experimental and numerical studies have demonstrated that rock failures are violent when LSS < λ (Cook 1965;Feng et al 2016;He et al 2015;Hudson et al 1972;Manouchehrian and Cai 2015;Zhao and Cai 2014). Unfortunately, ∆E in in these studies was not isolated to examine the influence of ∆E t on rock instability.…”

Section: Energy Transfer Energy Transfer Energy Transfermentioning

confidence: 99%

Influence of strain energy released from a test machine on rock failure process

Cai

2018

Can. Geotech. J.

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Abstract AbstractRock instability occurs if the energy supplied to the rock failure process is excess. The theoretical analysis on the energy transfer in rock failure process revealed that the rock failure process is a result of the strain energy released from the test machine or the surrounding rock masses of wall rock, plus the additional energy input from an external energy source if the deformation of the rock is continued and driven by the external energy source. The strain energy released from the test machine is focused in this study because it is responsible for some of the unstable rock failures in laboratory testing. A FEM-based numerical experiment was carried out to study the strain energy released from test machines under different loading conditions of LSS.The modeling results demonstrated that depending on the LSS of a test machine, the strain energy Accumulative energy input from an external energy source at peak load E r Accumulative energy consumed in a rock specimen at peak load E t Strain energy stored in a test machine at peak load E in * Accumulative energy input from an external energy source at post-peak deformation stage E r * Accumulative energy consumed in a rock specimen at post-peak deformation stage E t * Strain energy stored in a test machine at post-peak deformation stage ∆E in Energy input from an external energy source during post-peak deformation stage ∆E r Energy consumed in a rock specimen during post-peak deformation stage ∆E t Strain energy released from a test machine during post-peak deformation stage ∆E r B Energy item ∆E r under the ideal loading condition E p Post-peak stiffness of a rock specimen in stress-strain curve H Height of a column-shaped structure k Longitudinal stiffness of a column-shaped structure λ Post-peak stiffness of a rock specimen (absolute value)

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A Novel Mogi Type True Triaxial Testing Apparatus and Its Use to Obtain Complete Stress–Strain Curves of Hard Rocks

Cited by 199 publications

References 22 publications

Investigation of the Effect of Confining Pressure on the Mechanics-Permeability Behavior of Mudstone under Triaxial Compression

Investigation of the Effect of Confining Pressure on the Mechanics-Permeability Behavior of Mudstone under Triaxial Compression

Effect of the intermediate principal stress on the evolution of mudstone permeability under true triaxial compression

Influence of strain energy released from a test machine on rock failure process

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