A Mogi-Type True Triaxial Testing Apparatus for Rocks With Two Moveable Frames in Horizontal Layout for Providing Orthogonal Loads

Shi, Lu; Li, X.; Bai, Bing; Wang, A.; Zeng, Zhijiao; He, Hongqing

doi:10.1520/gtj20160242

Cited by 31 publications

(17 citation statements)

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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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“…Figure 6(b) shows that the natural logarithm of the differential pressure P associated with the first measurement decreases linearly over time. The stability and accuracy of the other subsystems of the TTA for the loading of the three principal stresses were also demonstrated by Shi et al 31 Specimens P4 and P15 were compressed at a low value of σ 2 (i.e., σ 2 σ 3 ), which means that they were compressed under conventional triaxial stress conditions. A comparison of the results shown in Figs 7 and 8(a) illustrates that the confining pressure has a significant impact on the change in permeability of the specimen under compression.…”

Section: Repeatability Testsmentioning

confidence: 65%

“…Figure (b) shows that the natural logarithm of the differential pressure Δ P associated with the first measurement decreases linearly over time. The stability and accuracy of the other subsystems of the TTA for the loading of the three principal stresses were also demonstrated by Shi et al …”

Section: Specimens and Test Proceduresmentioning

confidence: 85%

“…In addition, the axial splitting or shear propagation of microcracks parallel to the σ 2 direction can be accelerated because the in‐plane load of σ 2 can increase the stress intensity factor and reduce the normal stress on the microcracks . Thus, faults that form under conditions of σ 2 > σ 3 are flatter than those that form at σ 2 = σ 3 , and the roughness of the fault generally decreases with increasing σ 2 , as is illustrated by the failure of Dunham dolomite, Baoxing marble and the mudstone considered in this paper. Moreover, the fault forms due to a combination of axial splitting and shear failure of the microcracks, and the combined effects of σ 1 and σ 2 will cause more microcracks that are perpendicular to the σ 3 direction to split, which is why the fault becomes slightly steeper (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The mechanical and permeability tests were conducted at the Institute of Rock and Soil Mechanics, Chinese Academy of Sciences (WHRSM) with the RT3-II true triaxial apparatus (TTA) for rocks. [30][31][32] This apparatus consists of four subsystems: three subsystems for loading the maximum principal stress, intermediate principal stress and confining pressure and one subsystem for measuring the permeability (Figs 1 and 2). Therefore, the TTA can exert loads on a specimen in three directions independently and precisely using servos.…”

Section: Experimental Set-upmentioning

confidence: 99%

See 2 more Smart Citations

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 study of the end effect on the mechanical behaviors of rocks under true 3D compressions

Chen,

Che,

Gao

et al. 2024

Energy Science & Engineering

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In true triaxial compression tests, all three principal stresses are imposed independently. This allows for a more comprehensive analysis of the material's mechanical properties. The end effect in true triaxial compression tests is a crucial phenomenon that impacts the accuracy and reliability of the test results. In this study, a series of true triaxial compression tests is conducted to examine the influence of the end friction on the mechanical properties. The laboratory results show that the presence of the end friction could bring about an apparent increase in rock strength and also restrict the deformation in each direction showing that the stiffness (the slope of the curves) increased slightly. The rock strength could be enhanced from 24.7 to 90.7 () when the end friction is increased, which is mainly caused by the lateral interface friction. The failure mode and fracture angle of the specimen are also influenced by the end effect, showing that under high friction conditions, the failure is more ductile, and a larger fracture angle is observed. At last, in comparison with the published experimental data, the actual specific friction angle (corresponding friction coefficient is about 0.19) for the direct specimen–metal contacts in a true 3D test is numerically identified, which is empirically reasonable and higher than the tested range 0.146–0.157 obtained from double‐shear test system.

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A Mogi-Type True Triaxial Testing Apparatus for Rocks With Two Moveable Frames in Horizontal Layout for Providing Orthogonal Loads

Cited by 31 publications

References 31 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

Experimental study of the end effect on the mechanical behaviors of rocks under true 3D compressions

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