Статті в журналах: "True-triaxial loading"

1

Yin, Jian-Hua, Chun-Man Cheng, Md Kumruzzaman, and Wan-Huan Zhou. "New mixed boundary, true triaxial loading device for testing three-dimensional stress–strain–strength behaviour of geomaterials." Canadian Geotechnical Journal 47, no. 1 (January 2010): 1–15. http://dx.doi.org/10.1139/t09-075.

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This paper presents a brief review of true triaxial apparatuses (TTAs) developed in the past and their advantages and limitations. Considering the limitations of previous designs, a new true triaxial loading device that provides mixed boundary conditions for a true triaxial apparatus (TTA) is introduced. This loading device consists of four sliding rigid plates and two flexible loading faces. The setup of the loading device together with the whole true triaxial system is described. Frictions between sliding plates and the soil membrane surfaces in the new loading device are examined. A three-dimensional finite element (FE) modelling study is carried out on the stress and strain distribution of a soil specimen subjected to loading from two different loading devices. It is found that stresses and strains of a soil specimen subjected to loading from the new sliding plates are far more uniform than those subjected to loading from nonsliding plates with preset gaps. Finally, the paper presents the applications of the present TTA with the new loading device for testing studies of a completely decomposed granite soil and a geofoam. Typical results are presented and discussed. It is found that the present mixed boundary loading device is very suitable for true triaxial testing on both soils and geofoam, especially under large strains or compression without corner contact problems.

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2

Shi, L., C. C. Li, X. Zhang, X. T. Feng, and G. Wang. "Strength characteristics of brittle rock subjected to multi-stage intermediate principal stress loading." Géotechnique Letters 12, no. 2 (June 1, 2022): 1–17. http://dx.doi.org/10.1680/jgele.21.00021.

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A series of single-stage true triaxial compression (TTC) tests and multi-stage intermediate principal stress (σ2) loading tests were carried out on three types of brittle rock specimens in this study to examine the influence of σ2 and the validity of obtaining strength parameters by multi-stage loading method under true triaxial stress conditions. There exists a critical σ2 at which the rock strength reaches its ultimate value under both loading conditions. Under the same σ3 level, the critical σ2 is much smaller under the multi-stage σ2 loading than under the single-stage TTC. The test results also show that the strength determined under multi-stage σ2 loading is much smaller than that determined under single-stage TTC. The strength difference can reach 39%. A lower strength is measured under multi-stage σ2 loading because the local fracture plane induced by true triaxial stress is parallel to the σ2, and the strength of the rock specimen containing this type of local fracture plane is not affected by σ2. On the other hand, rock damage accumulates during multiple loading and unloading cycles. The current testing results indicate the multi-stage loading test is not suitable for determining the strength envelope of brittle rock under true triaxial conditions.

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3

Shen, Wei, Guang-Jian Liu, Lin-Ming Dou, Si-Yuan Gong, and Hu He. "Influences of True Triaxial Loading-Unloading Stress Paths on Mechanical Properties and Wave Velocity of Coal Samples subject to Risk of Rock Burst." Shock and Vibration 2021 (September 14, 2021): 1–14. http://dx.doi.org/10.1155/2021/4074159.

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To study fracture evolution and peak stress in burst risk coal samples (BRCSs) under true triaxial loading and unloading conditions, experimental and numerical research was applied to BRCSs under true triaxial stress paths entailing “x-direction displacement fixed, y-direction loading, z-direction unloading.” Both the experimental and the numerical results demonstrated that the peak stress borne by the BRCSs was not only affected by the initial stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR); therefore, peak stress equations of BRCSs under true triaxial loading and unloading conditions were established. The triaxial stress-time curves obtained by experiments and simulations exhibited an “elasticity-yield-destruction” phase, and the characteristics of the yield phase were determined by the RURLR. A typical BRCS was selected for velocity tomographic imaging to analyze the fracture evolution characteristics under true triaxial loading and unloading. The results showed that when the BRCS was subjected to a triaxial state of stress, the high- and low-velocity regions existed alternately due to the presence of the crack; during the elastic phase, the crack closed during loading in the previous phase was reopened upon unloading, so that the velocity of the sample decreased and a wide range of low-velocity regions could be formed; when entering the yield phase, the original crack continued to expand into a hole-through crack, leading to wider extreme values and ranges of these low- and high-velocity regions; at the breaking phase, multiple microcracks were generated around the hole-through cracks, decreasing the overall velocity, and showing point distributions characteristics of high- and low-velocity regions. Overall, many low-velocity regions with similar normal directions to the unloading direction were formed; these correlated well with macrofractures (postfailure).

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4

Karev, V. I., D. M. Kilmov, Yu F. Kovalenko, and K. B. Ustinov. "Experimental Study of Rock Creep under True Triaxial Loading." Mechanics of Solids 54, no. 8 (December 2019): 1151–56. http://dx.doi.org/10.3103/s0025654419080041.

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5

Reddy, Krishna R., and Surendra K. Saxena. "Liquefaction resistance of cemented sands under multidirectional cyclic loading." Canadian Geotechnical Journal 29, no. 6 (December 1, 1992): 989–93. http://dx.doi.org/10.1139/t92-108.

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This paper presents a methodology to predict liquefaction of uncemented and cemented sands under multidirectional cyclic loading conditions using solely conventional unidirectional cyclic test data. The method is found to be reasonably accurate based on the reported multidirectional cyclic test results using a true triaxial apparatus. Key words : sand, cementation, triaxial, experimental, theoretical, liquefaction.

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6

Shen, Wei, Lin-ming Dou, and Hu He. "Mechanical and Coal Burst Breeding Mechanism of Coal Samples under True Triaxial Loading and Unloading." Advances in Civil Engineering 2019 (November 11, 2019): 1–15. http://dx.doi.org/10.1155/2019/6050975.

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A true triaxial loading and unloading experiment entailing “y-direction stress loading, z-direction stress unloading, and x-direction displacement fixing” of coal samples was conducted. Through analysis of the stress characteristics, fracture characteristics, and energy evolution in coal samples, the mechanical and coal burst breeding mechanisms of coal samples under true triaxial loading and unloading were revealed. The experiment found that the yield stress and peak stress of coal samples were not only affected by the initial loading and unloading of lateral stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR), thereby establishing the stress equation of coal samples under a true triaxial loading and unloading. There was a yield turning point in the stress-time curve of coal samples, and the difference in triaxial stress and acoustic emission before, and after, yield was significant. It was found that a high unloading rate and high initial stress are precursors to coal sample bursting. During loading and unloading, the high-energy area expanded, but its location was always fixed to within a certain area. The energy in this area was rapidly released to form a burst source when the sample was subjected to high-speed unloading. The nonbursting coal samples and the burst coal samples showed characteristic slabbing and bursting behaviours, respectively: the former corresponding to the acoustic emission energy value being two orders of magnitude lower than the latter. The research results can provide a reference for the study of mechanical behaviours and coal burst criteria in the rock surrounding a coal roadway excavation.

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7

Wang, Shuai, Lianguo Wang, Jiansheng Tian, Hao Fan, Chongyang Jiang, and Ke Ding. "An Experimental Study on the Effects of True Triaxial Loading and Unloading Stress Paths on the Mechanical Properties of Red Sandstone." Minerals 12, no. 2 (February 5, 2022): 204. http://dx.doi.org/10.3390/min12020204.

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Loading and unloading stress paths play critical roles in investigating the deformation and failure of roadway excavation. In this study, tests under four different loading and unloading stress paths were conducted on red sandstone samples, with the aid of a self-developed true triaxial test system. Meanwhile, the deformation and failure characteristics of the samples were monitored during the tests. The following research conclusions were obtained: The octahedral shear stress is linearly correlated with the average effective stress, and the correlation coefficient R2 is 0.9825. The Mogi–Coulomb strength criterion is superior to the Drucker–Prager strength criterion in reflecting strength failure characteristics of red sandstone during loading and unloading. Shear failure tends to occur under uniaxial compression, whereas shear–tensile composite failure occurs under loading and unloading conditions. Compared with the true triaxial loading test, loading and unloading tests produce a larger strain in the unloading direction. Under loading and unloading stress paths, with the increase in intermediate principal stress (IPS), the strain in the direction of IPS gradually changes from expansion to compression, and the peak strength gradually increases. The state of IPS affects the failure strength of the sample and reflects the strengthening effect of IPS. This paper boasts a certain value and significance for research on the deformation and failure characteristics of sandstone in the actual in situ stress environment with triaxial dynamic changes.

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8

Karev, V. I., D. M. Klimov, Yu F. Kovalenko, and K. B. Ustinov. "Erratum to: Experimental Study of Rock Creep under True Triaxial Loading." Mechanics of Solids 55, no. 1 (January 2020): 154. http://dx.doi.org/10.3103/s0025654420010240.

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9

Cambou, B., A. Dogui, K. Jafari, and F. Sidoroff. "On the equivalence between true triaxial and torsion shear loading paths." Computers and Geotechnics 2, no. 4 (January 1986): 207–17. http://dx.doi.org/10.1016/0266-352x(86)90018-2.

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10

Alexeev, A. D., V. N. Revva, N. A. Alyshev, and D. M. Zhitlyonok. "True triaxial loading apparatus and its application to coal outburst prediction." International Journal of Coal Geology 58, no. 4 (June 2004): 245–50. http://dx.doi.org/10.1016/j.coal.2003.09.007.

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11

Wang, Xiaoliang, Zhen Zhang, and Jiachun Li. "Triaxial behavior of granular material under complex loading path by a new numerical true triaxial engine." Advanced Powder Technology 30, no. 4 (April 2019): 700–706. http://dx.doi.org/10.1016/j.apt.2018.12.020.

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12

Wang, Meng, Zheming Zhu, and Jun Xie. "An Experimental Study on Deformation Fractures of Fissured Rock around Tunnels in True Triaxial Unloads." Advances in Materials Science and Engineering 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/982842.

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Joints and cracks are frequently encountered in underground rock mass. During the process of tunnel excavations or other underground construction, the rock will be exposed suddenly, and such sudden unloading process will cause crack expansion and destabilize the rock structure. In order to investigate the crack behaviour during this process, a true triaxial loading apparatus with a computer-controlled electrohydraulic servosystem was established, and a series of true triaxial loading and unloading experiments was conducted by using concrete specimens containing inclined cracks with inclinations of 15°, 30°, 45°, 60°, and 75°. The stress-strain behavior and the failure property of rock models during unloading process were obtained, and, additionally, the coefficient of brittle stress drop was investigated. The uniaxial compression tests were simulated by using finite element method.

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13

Browning, John, Philip G. Meredith, Christopher Stuart, Sophie Harland, David Healy, and Thomas M. Mitchell. "A Directional Crack Damage Memory Effect in Sandstone Under True Triaxial Loading." Geophysical Research Letters 45, no. 14 (July 20, 2018): 6878–86. http://dx.doi.org/10.1029/2018gl078207.

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14

Zhai, Shaobin, Guoshao Su, Shunde Yin, Sizhou Yan, Zhengfu Wang, and Liubin Yan. "Fracture evolution during rockburst under true-triaxial loading using acoustic emission monitoring." Bulletin of Engineering Geology and the Environment 79, no. 9 (June 10, 2020): 4957–74. http://dx.doi.org/10.1007/s10064-020-01858-z.

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15

Zhang, Yingjie, Jiangteng Li, Gang Ma, and Shuangfei Liu. "Unloading Mechanics and Energy Characteristics of Sandstone under Different Intermediate Principal Stress Conditions." Advances in Civil Engineering 2021 (April 22, 2021): 1–9. http://dx.doi.org/10.1155/2021/5577321.

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The TRW-3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different σ 2 , and the true triaxial lateral unloading mechanics and energy characteristics of sandstone under different σ 2 were studied. The experimental results show the following: (1) compared with the results of the loading test, the peak strength of the sandstone under the unloading σ 3 path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of σ 2 ; sudden brittle failure occurs at the end of unloading. E gradually decreases with the increase of H, and it performs well to use the cubic polynomial to fit the curve of E-H. (2) The Mogi–Coulomb strength criterion can accurately describe the true triaxial strength characteristics of sandstone under loading and unloading conditions. Compared with the results of the loading test, the values of c and φ obtained based on this criterion under the unloading σ 3 path are reduced. (3) Under the condition of unloading σ 3 , U, U e , and U d , when the specimen is broken, are all linearly positively correlated with σ 2 . U d increases nonlinearly with the increase of H, and as σ 2 increases, the slope of the U d -H curve becomes larger, and the specimen consumes more energy under the same unloading amount. Most of the energy absorbed by the specimen under the unloading σ 3 path is converted into U e , but as σ 2 increases, U d / U increases, and the energy consumed when the specimen is broken is greater.

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16

Wang, Gang, Pengfei Wang, Yangyang Guo, and Wenxin Li. "A Novel True Triaxial Apparatus for Testing Shear Seepage in Gas-Solid Coupling Coal." Geofluids 2018 (September 2, 2018): 1–9. http://dx.doi.org/10.1155/2018/2608435.

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To study the effects of shear stress on the mechanical and seepage properties of gas-bearing coal in three-dimensional stress conditions, a novel true triaxial apparatus (TTA) was developed for the rigid loading of the major principal stress σ1 and the intermediate principal stress σ2, and for the flexible loading of the minor principal stress σ3. Both the upper and lateral pressure heads do not interfere with each other when loading σ1 and σ2. The control and measurement of gas flow sealed effectively in coal samples were achieved by using a gas seepage system. The TTA was used to perform a series of experiments on shear seepage in coal samples under true triaxial stress conditions. The experimental results about coal’s shear failure modes, shear stress-shear displacement curve, and permeability-shear displacement curve all showed that the TTA with its better accuracy and reliability had advantages in studying the effects of both the intermediate principal stress and shear deformation on the mechanical properties of coal samples and on the characteristics of gas seepage. Thus, it could provide a new test means for further studies on shear-induced seepage in the gas-solid coupling coal.

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17

Sammonds, Peter R., S. Boon, N. Hughes, and M. A. Rist. "Flow of anisotropic ice from the EPICA core: a new test apparatus." Annals of Glaciology 30 (2000): 1–7. http://dx.doi.org/10.3189/172756400781820732.

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AbstractOur objective is to measure the mechanical properties of anisotropic ice of the EPICA ice core, from Dome Concordia, Antarctica, through the full depth of the borehole in deformation experiments under simulated ice-sheet conditions of temperature and pressure. We propose to undertake experiments on the EPICA core using both a conventional triaxial-test apparatus and a new, true, triaxial-test apparatus incorporating automated tomographic imaging of the ice-fabric evolution during deformation. We present the design of this new apparatus together with our testing methodology for EPICA ice. The new apparatus is capable of deforming an ice specimen, up to 200 mm × 100 mm × 40 mm, under servo-controlled biaxial loading with a superimposed confining pressure of 50 MPa and at temperatures down to –40°C. Highly unusual problems arising from the true triaxial nature of the apparatus and tomographic imaging are discussed.

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18

Peng, Yanyan, Haoxiang Deng, Minghong Xing, Pengfei Guo, and Chun Zhu. "Research on Coal Mechanical Properties Based on True Triaxial Loading and Unloading Experiment." Advances in Civil Engineering 2021 (March 15, 2021): 1–10. http://dx.doi.org/10.1155/2021/6675222.

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To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.

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19

Cha, Minsu, Naif B. Alqahtani, Bowen Yao, Xiaolong Yin, Timothy J. Kneafsey, Lei Wang, Yu-Shu Wu, and Jennifer L. Miskimins. "Cryogenic Fracturing of Wellbores Under True Triaxial-Confining Stresses: Experimental Investigation." SPE Journal 23, no. 04 (February 6, 2018): 1271–89. http://dx.doi.org/10.2118/180071-pa.

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Summary A laboratory study of cryogenic fracturing was performed to test its ability to improve oil/gas recovery from low-permeability reservoirs. Our objective is to develop well-stimulation technologies using cryogenic fluids [e.g., liquid nitrogen (LN)] to increase permeability in a large reservoir volume surrounding wells. The new technology has the potential to reduce formation damage caused by current stimulation methods and minimize or eliminate water usage. The concept of cryogenic fracturing is that a sharp thermal gradient (thermal shock) created at the surfaces of formation rocks by applying cryogenic fluid can cause strong local tensile stress and start fractures. We developed a laboratory system for cryogenic fracturing under true-triaxial loading, with LN-delivery/control and -measurement systems. The loading system simulates confining stresses by independently loading each axis up to approximately 5,000 psi on 8×8×8-in. cubes. Temperature in boreholes and at block surfaces and fluid pressure in boreholes were continuously monitored. Acoustic and pressure-decay measurements were obtained before and at various stages of stimulations. Cubic blocks (8 × 8×8-in.) of Niobrara shale, concrete, and sandstones were tested, and stress levels and anisotropies varied. Three schemes were considered: gas fracturing without cryo-stimulation, gas fracturing after low-pressure cryogen flow-through, and gas fracturing after high-pressure cryogen flow-through. Results from pressure-decay tests show that LN stimulation clearly increases permeability, and repeated stimulations further increase the permeability. Acoustic velocities and amplitudes decreased significantly after cryo-stimulation, indicating fracture creation. In the gas fracturing without the stimulation, breakdown (complete fracturing) occurs suddenly without any initial leaking, and major fracture planes form along the plane containing principal-stress and intermediate-stress directions, as expected theoretically. However, in the gas fracturing after cryogenic stimulations, breakdown occurred gradually and with massive leaking because of thermal fractures created during stimulation. In addition, the major fracture direction does not necessarily follow the plane containing the principal-stress direction, especially at low confining-stress levels. In tests, we observed that cryogenic stimulation seems to disrupt the internal stress field. The increase in borehole temperature after stimulation affects the permeability of the specimen. When a stimulated specimen is still cold, it maintains high permeability because fractures remain open and local thermal tension is maintained near the borehole. When the rock warms back, fractures close and permeability decreases. In these tests, we have not used proppants. Overall, fractures are clearly generated by low- and high-pressure thermal shocks. The added pressure of the high-pressure thermal shocks helps to further propagate cryogenic fractures generated by thermal shock. Breakdown pressure is significantly lowered by LN stimulation, with observed breakdown-pressure reductions up to approximately 40%.

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20

Karev, Vladimir, Yurii Kovalenko, Valerii Khimulia, and Nikolai Shevtsov. "Parameter determination of the method of directional unloading of the reservoir based on physical modelling on a true triaxial loading setup." Journal of Mining Institute 258 (December 30, 2022): 906–14. http://dx.doi.org/10.31897/pmi.2022.95.

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The article presents a theoretical and experimental substantiation of the method of directional unloading of the reservoir in fields with low-permeability reservoirs. The relevance of the article is due to the reduction of hydrocarbon resources in modern conditions and the need to create new efficient environmentally friendly technologies to develop hydrocarbon deposits with hard-to-recover reserves, primarily with low-permeability reservoirs. The results of a theoretical study of the stress-strain state in the vicinity of a well, both cased and open, are presented. They are necessary to develop programs for laboratory testing of core specimens from the studied fields. A technique for physical modelling of deformation processes in the bottomhole zone with a decrease in pressure at the well bottom in a true triaxial loading unit is described in order to determine the parameters of the process impact on the formation reservoir, leading to an increase in well productivity. The method was applied to the conditions of the low-permeability reservoir at the Verkhneviluchanskoye oil and gas condensate field in the southwest of the Republic of Sakha (Yakutia). Expe-rimental studies were carried out on a unique scientific unit for true triaxial loading, created at the IPMech RAS, the Triaxial Independent Loading Test System. The directional unloading method was adapted for the studied field, the process parameters of successful application of the method were determined: the bottomhole design, the drawdown values necessary to increase the permeability of the bottomhole formation zone.

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21

Liu, Jianjun, Zheming Zhu, and Bo Wang. "The Fracture Characteristic of Three Collinear Cracks under True Triaxial Compression." Scientific World Journal 2014 (2014): 1–5. http://dx.doi.org/10.1155/2014/459025.

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The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses.

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22

Ren, Biao, Tengjiao Wang, Jinyu Xu, Zhihang Wang, Yan Lv, and Yipeng Ning. "Research on the True Triaxial Mechanical Properties of Concrete under the Coupling Action of High Temperature and Biaxial Unequal Lateral Pressure." Materials 15, no. 14 (July 19, 2022): 5014. http://dx.doi.org/10.3390/ma15145014.

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Based on engineering practice and practical needs, this paper takes ordinary concrete specimens as the research object, and adopts a high-temperature true triaxial loading test system to carry out high-temperature uniaxial and true triaxial static compression tests of concrete under high-temperature conditions. By comparing with normal temperature conditions, this paper analyzes the influence of the coupling effect of high-temperature and biaxial unequal lateral pressure on the static mechanical properties of concrete. By analyzing the experimental data, we reached a series of conclusions and carried out theoretical research on this basis. High temperatures can significantly affect the uniaxial static pressure strength characteristics, deformation characteristics, and failure mode of concrete. When the temperature exceeds 400 °C, the compressive strength decreases significantly, the peak strain increases sharply, and the plasticity of concrete is further enhanced. The coupling effect of high-temperature deterioration and lateral pressure strengthening makes the true triaxial mechanical properties of concrete change significantly; 0.6:0.2 and 400 °C are the turning points of side pressure ratio and temperature that affect the change law of the true triaxial mechanical properties of concrete, respectively. Based on the study of the high-temperature deterioration factor and lateral pressure strengthening factor, this paper further puts forward a concrete strength formula under the coupling action of high temperature and biaxial unequal lateral pressure. It was verified that the formula has a high accuracy.

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23

Liu, Yiming, Xinchao Liao, Lihua Li, and Haijun Mao. "Discrete Element Modelling of the Mechanical Behavior of Sand–Rubber Mixtures under True Triaxial Tests." Materials 13, no. 24 (December 15, 2020): 5716. http://dx.doi.org/10.3390/ma13245716.

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Sand–rubber mixtures (SRMs) consisting of stiff sand particles and soft rubber particles are typical binary mixture materials that possess a variety of complicated properties. The complexity of the properties of sand–rubber mixtures is increased when complex stress path is involved. This study investigates the mechanical behavior of sand–rubber mixtures under generalized loading conditions using the discrete element method. A series of numerical true triaxial shear tests were conducted on pure sand and sand–rubber mixtures. The effect of rubber content and loading path on both of the macroscopic and microscopic performances of sand–rubber mixtures was investigated, and the associated microscale mechanism was also discussed. Numerical simulations show that the relationship between the peak friction angle ϕp and the intermediate principal stress ratio b is influenced by the addition of rubber particles, and a suggested explanation of this phenomenon is that the rubber particles mainly affect the inherent stability of the strong network. Particle-scale observations, including the coordinate number, the proportion of strong contacts, and the fabric anisotropy, are also presented in this study. Microscopic results confirm the explanation above, and explore the force transmission characteristics of sand–rubber mixtures under generalized loading conditions. This research can provide a reference for the constitutive model development of sand–rubber mixtures.

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24

Zhang, Y., J. Zhang, W. Du, H. Wang, and K. Niu. "Gas Seepage Under Continuous and Step Loading Based on True Triaxial Seepage Test Apparatus." Experimental Techniques 45, no. 2 (January 8, 2021): 121–32. http://dx.doi.org/10.1007/s40799-020-00418-0.

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25

Zhang, Ran, Jie Liu, Zhanyou Sa, Zaiquan Wang, Shouqing Lu, and Zhaoyang Lv. "Fractal characteristics of acoustic emission of gas-bearing coal subjected to true triaxial loading." Measurement 169 (February 2021): 108349. http://dx.doi.org/10.1016/j.measurement.2020.108349.

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26

Su, Guoshao, Zhiyong Chen, J. Woody Ju, and Jianqing Jiang. "Influence of temperature on the strainburst characteristics of granite under true triaxial loading conditions." Engineering Geology 222 (May 2017): 38–52. http://dx.doi.org/10.1016/j.enggeo.2017.03.021.

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27

Hu, Shaobin, Xiaochun Li, and Bing Bai. "Effects of different fluids on microcrack propagation in sandstone under true triaxial loading conditions." Greenhouse Gases: Science and Technology 8, no. 2 (October 31, 2017): 349–65. http://dx.doi.org/10.1002/ghg.1744.

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28

Alexeev, A. D., V. N. Revva, L. L. Bachurin, and I. Y. Prokhorov. "The effect of stress state factor on fracture of sandstones under true triaxial loading." International Journal of Fracture 149, no. 1 (January 2008): 1–10. http://dx.doi.org/10.1007/s10704-008-9214-6.

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29

Rong, Tenglong, Can Guan, Keliu Liu, Shuai Heng, Wenlong Shen, and Ruiyong Mou. "A Statistical Damage Constitutive Model of Anisotropic Rock: Development and Validation." Geofluids 2021 (August 12, 2021): 1–16. http://dx.doi.org/10.1155/2021/6307895.

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The damage constitutive model is of great significance to research the stress-strain relationship and damage evolution of rock under loading in engineering. In order to investigate the effect of anisotropic characteristic on the stress-strain relationship and damage evolution, a statistical damage constitutive model of anisotropic rock under true triaxial condition was developed. In this study, the plane which existed perpendicular to the coordinate axis was extracted from representative volume element (RVE) of rock. The extracted plane was assumed to be composed of abundant mesoscopic elements whose failure strength satisfied the Weibull distribution. According to the number of failure elements on the plane in each direction under loading, the anisotropic damage variable was established based on the proposed concept of areal damage. A statistical damage constitutive model of anisotropic rock was developed by using strain equivalent hypothesis and generalized Hooke constitutive model. Subsequently, the parameters in the anisotropic damage constitutive model were determined by the method of total differential. Thus, the damage evolution of anisotropic rock under various stress conditions can be conveniently evaluated by the anisotropic damage model. The model was validated based on the tests of rocks under the stress conditions of conventional triaxial and true triaxial, respectively. Moreover, for the purpose of studying the influence of parameters on the model, sensitivity analyses of mechanical parameters and model parameters were carried out. The results of statistical damage constitutive clearly demonstrate the stress-strain and damage evolution of anisotropic rock under various stress conditions.

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30

ZHANG, RAN, JIE LIU, ZHANYOU SA, ZAIQUAN WANG, SHOUQING LU, and CHENGFENG WANG. "EXPERIMENTAL INVESTIGATION ON MULTI-FRACTAL CHARACTERISTICS OF ACOUSTIC EMISSION OF COAL SAMPLES SUBJECTED TO TRUE TRIAXIAL LOADING–UNLOADING." Fractals 28, no. 05 (August 2020): 2050092. http://dx.doi.org/10.1142/s0218348x20500929.

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Coal–rock dynamic disasters seriously threaten safe production in coal mines, and an effective early warning is especially important to reduce the losses caused by these disasters. The occurrence of coal–rock dynamic disasters is determined by mining-induced stress loading and unloading. Therefore, it is of great significance to analyze the precursory information of coal deformation and failure during true triaxial stress loading and unloading. In this study, the deformation and failure of coal samples subjected to true triaxial loading and unloading, including fixed axial stress and unloading confining stress (FASUCS), are experimentally investigated. Meanwhile, acoustic emission (AE) during the deformation of coal samples is monitored, and the multi-fractal characteristics of AE are analyzed. Furthermore, combined with the deformation and failure of coal samples, the precursory information of coal deformation and rupture during true triaxial stress loading and unloading is obtained. Finally, the relationship between multi-fractal characteristics and damage evolution of coal samples under FASUCS is discussed. The results show that the multi-fractal spectral widths of AE time series under the conditions of FASUCS with different initial confining stresses or unloading rates are quite different, but the dynamic changes of multi-fractal parameters [Formula: see text] and [Formula: see text] are similar. This indicates that the microscopic complexity of AE events of coal samples under different conditions of FASUCS differs, but the macroscopic generation mechanism of AE events has inherent uniformity. The dynamic changes of [Formula: see text] and [Formula: see text] can reflect the stress and damage degree of coal samples. The dynamic change process of [Formula: see text] well accords with the damage evolution process of coal samples. A gradual decrease of [Formula: see text] corresponds to a slow increase of damage, while a sharp increase of it corresponds to a rapid growth of damage. At the same time, the mutation point of damage curve at distinct stress difference levels shares the same variation trend with the [Formula: see text] mutation point. The change of [Formula: see text] can reflect the damage process of coal samples, which can be used as precursor information for predicting coal–rock rupture. The finding is of great significance for the early warning of coal–rock dynamic disasters.

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31

Wibisono, D. Y., K. Arora, D. Majumder, and M. Gutierrez. "Laboratory-Scale Rockburst Physical Model Testing Using a True-Triaxial Cell." IOP Conference Series: Earth and Environmental Science 1124, no. 1 (January 1, 2023): 012039. http://dx.doi.org/10.1088/1755-1315/1124/1/012039.

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Abstract Assessment of rockburst risk is one of the most fundamental challenges in tunnel design and construction in rocks. The rockburst phenomenon is typically related to rock brittle failure properties, which result in significant strain-energy release, spalling, fractures, and damage near the tunnel opening. This research aims to present a preliminary analysis of rockburst in an unsupported circular tunnel using a novel experimental approach to model tunnel boring machine excavated opening through brittle fracture material. In this physical model testing, the true-triaxial cell utilizes a cube of synthetic sandstone of 300 mm dimensions with a freshly excavated 51 mm diameter tunnel, 150 mm depth on the center top side using a miniature tunnel boring machine. The six sides of the specimen cube are loaded in a true-triaxial manner, allowing for various magnitudes of principal stresses and stress levels that reflect actual in-situ conditions. In addition, the experimental setup employs acoustic emission monitoring to observe the tunnel response during excavation and loading increment. However, the sample in this preliminary experiment was loaded under hydrostatic circumstances and gradually increased until the sample showed a reduction in the acoustic emission activity and failed. The experiment results suggest that the physical model can better understand rockburst in a tunnel through the acoustic emission analysis. The model can outline the damage and spalling during strain energy release near the tunnel boundary.

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32

Xu, Wendong, Xuefeng Li, Xilin Lü, and Wenwei Yang. "Cyclic True Triaxial Tests on Aeolian Sand Considering Initial Shear Effect." Sustainability 14, no. 24 (December 13, 2022): 16730. http://dx.doi.org/10.3390/su142416730.

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Under traffic loading, the soil elements in subgrade are subjected to a complex 3D stress path. To investigate the cyclic behavior of desert subgrade under initial shear stress conditions, the number of cyclic true triaxial tests were implemented on aeolian sand from the Tengger Desert. A large range of initial shear stress levels and different cyclic stress paths (various combinations of cyclic major and intermediate principal stresses) were designed in the experiments. The results show that the initial shear stress level significantly influences the cyclic response, and the response mode of aeolian sand under initial shear stress is incremental failure and elastic shakedown, while it is critical failure without initial shear stress. With the increase in initial shear stress, the permanent strain increases first and then decreases, with the maximum permanent strain occurring at q0 = 50 kPa. Moreover, by comparing the test data under different cyclic stress paths, it is found that the cyclic resistance decreases with the increase in the coefficient of cyclic intermediate principal stress bcyc. Compared to the limiting pore pressure criterion, the conventional 5% axial strain failure criterion may overestimate the cyclic resistance, leading to unsafe evaluation and design. Therefore, by using the pore pressure criterion, the relationship between the limit pore pressure ratio and the initial stress condition was investigated and it was found that the limit pore pressure ratio decreased linearly when the initial shear stress increased.

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33

Hoyos, Laureano, Roya Davoodi-Bilesavar, Ujwalkumar Patil, Jairo Yepes-Heredia, Diego Pérez-Ruiz, and José Cruz. "Behavior of unsaturated cohesive-frictional soils over a whole range of suction/thermo-controlled stress paths and modes of deformation." Soils and Rocks 44, no. 3 (July 20, 2021): 1–12. http://dx.doi.org/10.28927/sr.2021.066621.

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The present work documents some of the most recent experimental evidence of the thermohydro-mechanical behavior of compacted soils over a whole range of suction- and/or thermo-controlled stress paths and modes of deformation, including data from a series of triaxial, true triaxial, plane strain, ring shear, and resonant column tests conducted on different types of cohesive-frictional soils in the low-to-medium matric suction range under either room temperature or thermally controlled conditions. The work has been accomplished at the Advanced Geomechanics Laboratory of the University of Texas at Arlington, focusing primarily on the following essential features of unsaturated soil behavior: (1) Loading-collapse and apparent tensile strength loci assessed from suction-controlled triaxial and true triaxial testing on clayey sand, (2) Critical state lines from suction-controlled plane strain testing on silty soil, (3) Peak and residual failure envelopes from suction-controlled ring shear testing on clayey soil, (4) Frequency response curves and cyclic stress-strain hysteretic loops from thermo-controlled, constant-water content resonant column testing on clayey soil, and (5) Residual failure envelopes from suction/thermo-controlled ring shear testing on clayey soil. The work is intended to serve as a succinct yet reasonably thorough state-of-the-art paper contribution to PanAm-UNSAT 2021: Third Pan-American Conference on Unsaturated Soils, Rio de Janeiro, Brazil, July 21-25, 2021.

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34

Cabrejos-Hurtado, J., S. Galindo Torres, and D. M. Pedroso. "Assessment of the Mechanical Behaviour of Granular Media by DEM-Based True Triaxial Tests." Applied Mechanics and Materials 846 (July 2016): 428–33. http://dx.doi.org/10.4028/www.scientific.net/amm.846.428.

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This study presents the numerical simulation of a true triaxial test by means of the discrete element method (DEM). Experimental results performed on Toyoura sand are employed as reference and the calibration methodology is explained. Physical aspects of the real soil, such as the grain size distribution and the relative density, are considered during the generation of the virtual sample. It is shown that the main aspects of the macro-mechanical behaviour of granular soils during compression loading can be fairly represented by the idealised simulations with particles.

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35

Xie, Wen-Bo, Guan-Lin Ye, Qi Zhang, Jin-Jian Chen, and Feng Zhang. "A New True Triaxial Apparatus for Finite Deformation with a Novel Rigid–Flexible Loading Device." Geotechnical Testing Journal 45, no. 4 (May 11, 2022): 20210264. http://dx.doi.org/10.1520/gtj20210264.

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36

Hu, Huarui, Binwei Xia, Yafei Luo, and Jiajun Peng. "Energy characteristics of sandstones with different crack angles under true triaxial cyclic loading and unloading." Energy Science & Engineering 10, no. 4 (March 13, 2022): 1418–30. http://dx.doi.org/10.1002/ese3.1110.

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37

Gao, Yaohui, and Xia-Ting Feng. "Study on damage evolution of intact and jointed marble subjected to cyclic true triaxial loading." Engineering Fracture Mechanics 215 (June 2019): 224–34. http://dx.doi.org/10.1016/j.engfracmech.2019.05.011.

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38

Lu, Jun, Guangzhi Yin, Dongming Zhang, Heng Gao, Cunbao Li, and Minghui Li. "True triaxial strength and failure characteristics of cubic coal and sandstone under different loading paths." International Journal of Rock Mechanics and Mining Sciences 135 (November 2020): 104439. http://dx.doi.org/10.1016/j.ijrmms.2020.104439.

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39

Browning, J., P. G. Meredith, C. E. Stuart, D. Healy, S. Harland, and T. M. Mitchell. "Acoustic characterization of crack damage evolution in sandstone deformed under conventional and true triaxial loading." Journal of Geophysical Research: Solid Earth 122, no. 6 (June 2017): 4395–412. http://dx.doi.org/10.1002/2016jb013646.

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40

Mutaz, E., M. Serati, D. J. Williams, and O. S. Quintero. "Validation of the Crack Mode-Changing Stress in Circular Tunnels Under Generalized Triaxial Tensile Stress States." IOP Conference Series: Earth and Environmental Science 1124, no. 1 (January 1, 2023): 012068. http://dx.doi.org/10.1088/1755-1315/1124/1/012068.

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Abstract In the past century, mining depths have increased profoundly from a few hundred meters to several kilometres following improvements in drilling techniques and instrumentation methods. In highly-stressed tunnels, the predominant failure mechanism of underground rock is controlled by stress-induced fractures parallel to the excavation boundaries in terms of spalling failures or, in some severe cases, a violent slab ejection that forms a V-shaped notch around the excavation walls. Such failures can seriously affect production and shut down the operation temporarily or even permanently. To better characterize, predict, and prevent these catastrophic failures, many laboratory tests and scaled model tunnels have been conducted under uniaxial and biaxial loading conditions, with limited studies also available under true triaxial stress states. This paper extends the previous studies on the impact of true triaxial loading conditions on the spalling failure in high porosity sandstone and investigates further the validation of a new Crack Mode-Changing Stress (CMCS) parameter, defined as the minimum principal stress required to change rock fracturing from splitting to a sliding failure mode. The results revealed that the minor principal stress can significantly affect the propagation of the stress-induced fractures of spalling failure along the tunnel sidewall.

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41

Wang, Man, Weihang Du, Yingwei Wang, Xinjian Li, Liming Qiu, Beichen Yu, Zehua Niu, and Dongming Zhang. "The Effects of True Triaxial Loading and Unloading Rates on the Damage Mechanical Properties of Sandstone." Sustainability 14, no. 19 (September 21, 2022): 11899. http://dx.doi.org/10.3390/su141911899.

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Coal is the main energy source in China. In the process of coal resource mining, the surrounding rock of roadways is often in the complex stress environment of “three heights and one disturbance”. At the same time, rocks in the stratum are often in a three-way unequal pressure state under the action of geological structure, and conventional rock mechanics tests cannot study the mechanical properties of rocks under actual stress conditions; thus, this is based on the self-developed true triaxial multifunctional fluid–structure coupling test system to study the damage mechanical Properties of Sandstone. The results are shown as follows: With an increase in loading rate, the peak damage Dcr of sandstone decreases, but the initial damage Da increases in the elastic stage, and the brittleness of sandstone weakens. With the increase in the unloading rate, Dcr increases, but Da decreases in the elastic stage, and the sandstone brittleness increases first, then decreases. In addition, the peak maximum principal strain ε1maxfirst decreases rapidly and then slowly; the peak minimum principal strain ε3max increases first, then decreases slowly, and increases slowly; the peak intermediate principal strain ε2max decreases slowly; and the peak volume strain εvmax increases rapidly first and then slowly with increases in the loading rate. With an increase in the unloading rate, ε1max increases rapidly first, then decreases slowly, then increases rapidly and finally increases slowly; ε3max first decreases slowly, then increases slowly, and finally decreases slowly; and ε2max increases slowly then decreases slowly. εvmax decreases rapidly first and then increases slowly with increasing loading rate.

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42

Couture, Cyrille-B., and Pierre Bésuelle. "Diffuse and localized deformation of a porous Vosges sandstone in true triaxial conditions." E3S Web of Conferences 92 (2019): 06007. http://dx.doi.org/10.1051/e3sconf/20199206007.

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This work presents an experimental study on the diffuse and localized deformation mechanisms of a high porosity (20%) Vosges sandstone (Eastern France) subjected to different stress paths in the deviatoric plane. The experimental campaign was performed using a high pressure true triaxial apparatus (TTA) in which the three principal stresses are independently controlled. A series of 10 quasi-static, monotonous loading tests was performed at 2 constant mean stresses, in the brittle-ductile transition regime, and at five prescribed Lode angles, from axisymmetric compression (ASC) to axisymmetric extension (ASE), as a measure of the deformation mode. The failure surface in each deviatoric plane and changes in macroscopic measurements, such as deformation band angles tracked by full field digital image correlation (DIC) technology, indicate a clear effect of the Lode angle on a transition between the brittle and ductile regime, independent from the mean stress level.

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43

Xu, Lei, and Fengqiang Gong. "Experimental Study of Strain Rockburst considering Temperature Effect: Status-of-the-Art and Prospect." Shock and Vibration 2021 (November 10, 2021): 1–15. http://dx.doi.org/10.1155/2021/8767592.

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In deep mining and excavation of tunnels with high geothermal, the surrounding rock is not only subjected to high ground stress but also subjected to high temperature. Temperature will change mechanical characteristics and energy storage capacity of rocks, as well as increase the destructiveness and randomness of rockburst. To reveal the mechanism of high-temperature strain burst in deep rock, the rockburst tests from uniaxial compression to three-dimensional compression were reviewed, and the research results of the minimum principal stress rapid unloading, true-triaxial loading with one free face, and dynamic disturbance triggered pre-heated granite rockburst simulation tests were focused on. According to the occurrence state of country rock for deep high-temperature and stress state in the whole process during excavation, six development directions for high-temperature strain rockburst simulation tests were proposed: (1) constructing the damage constitutive models of high-temperature rocks according to linear energy dissipation law; (2) developing the true triaxial rockburst simulation testing system accomplishing the function of “real-time high temperature + unloading + dynamic disturbance”; (3) considering the true triaxial rockburst simulation test after microwave irradiation; (4) developing the real-time high-temperature rockburst simulation testing device for large-size specimens and internal unloading; (5) focusing on the energy actuating mechanism for deep high-temperature rock failure via rockburst simulation tests; and (6) implementing the three-dimensional rockburst simulation test on the basis of deep in situ coring.

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44

Huang, Wen Xiong, Erich Bauer, and Scott William Sloan. "Prediction of Pressure and Density Dependent Failure in Sand-Like Granular Materials under General Stress Conditions." Key Engineering Materials 340-341 (June 2007): 1243–48. http://dx.doi.org/10.4028/www.scientific.net/kem.340-341.1243.

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This paper presents a theoretical study of failure modes in sand-like granular materials under general triaxial stress conditions based on a hypoplastic model and a bifurcation analysis. The well developed constitutive model contains the void ratio as a state variable which allows the pressure and density dependent behaviour of the granular materials to be described with a single set of state-independent constitutive parameters. Based on this model a shear bifurcation condition is derived. Loading along various stress paths that can be achieved with a true triaxial test apparatus are simulated numerically. Either localized failure or uniform diffuse failure in granular samples may occur, which is determined based on whether the shear bifurcation condition is met. Effects of confining pressure and initial density are discussed.

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45

Xu, Y. H., M. Cai, X. W. Zhang, and X. T. Feng. "Influence of end effect on rock strength in true triaxial compression test." Canadian Geotechnical Journal 54, no. 6 (June 2017): 862–80. http://dx.doi.org/10.1139/cgj-2016-0393.

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The influence of the end effect on rock strength in true triaxial compression testing was studied using a numerical approach. The influence of the intermediate principal stress (σ2) on rock strength was isolated by using the two-dimensional Mohr–Coulomb failure criterion that depends only on the major principal stress (σ1) and minor principal stress (σ3). Thus, any enhancement to the rock strength with the increase of σ2 can be attributed to the end effect. It was shown that the end effect can result in an apparent σ2 effect, as long as the coefficient of friction (μ) at the rock specimen – steel platen contacts is not zero and the specimen in the σ2 loading direction is squat. When the strengthening due to the increase of σ2 predicted by a theoretical failure criterion was added to the strengthening due to the end effect, the results were in good agreement with the observed σ2 effect from some previous laboratory tests, indicating that the observed σ2 effect in true triaxial compression testing could be partially influenced by the end effect, particularly when σ3 was low. It is suggested to decrease the end effect to a level where the apparent σ2 effect is very small so that the obtained test results are more meaningful to characterize the actual σ2 effect.

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46

Sun, Feiyue, Junqi Fan, Jiaqi Guo, and Xiliang Liu. "Experimental and Numerical Investigation of Energy Evolution Characteristic of Granite considering the Loading Rate Effect." Advances in Materials Science and Engineering 2022 (September 20, 2022): 1–20. http://dx.doi.org/10.1155/2022/8260107.

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In order to investigate the loading rate effect of energy evolution in granite, the indoor physical simulation test of single face fast unloading-three directions and five faces stress-vertical continuous loading under different loading rates was conducted using a new true triaxial rockbursttest system. The energy accumulation-dissipation-release characteristics in the process of rock deformation and failure were revealed. Based on the three-dimensional discrete element theory and the polycrystalline modeling technique (randomly generated Voronoi mineral grains), the entire process of rockburst inoculation-occurrence-development, as well as the energy evolution characteristics under true triaxial single face unloading conditions, were studied. The test results indicate that the energy transport and conversion of rock samples under different loading rates exhibit distinct stage characteristics. It can be divided into the initial energy accumulation stage, steady energy accumulation stage, rapid energy dissipation stage, and rapid energy release stage. With a rise in loading rate, the specimen in the process of energy accumulation is accompanied by energy dissipation, more external input energy, and elastic strain energy release amount into the kinetic energy of fragments, resulting in the rockburst phenomenon. As the loading rate increases, the elastic strain energy conversion rate (Ue/U) falls, while the dissipative energy conversion rate (Ud/U) increases. The higher the elastic strain energy conversion rate and the lower the dissipative energy conversion rate, the more serious the rockburst occurs. Numerical simulation results show that the entire process of rockburst inoculation-occurrence-development is successfully simulated using the crystal scale fine model (CSFM) considering the grain mineral composition. The ejection failure process can be divided into four stages, including grains ejection, rock spalling into plates, rock shearing into fragments, and rock fragments ejection. The relationships between the peak strength, elastic strain energy of rock samples, and loading rates are obtained, which is consistent with the laboratory test results. The high rate linear growth of kinetic energy evolution between the two inflection points can provide precursor information for rockburst prediction.

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47

Hu, Chuanyu, Fuding Mei, and Wakeel Hussain. "Wavelet Energy Evolution Characteristics of Acoustic Emission Signal under True-Triaxial Loading during the Rockburst Test." Applied Sciences 12, no. 15 (August 2, 2022): 7786. http://dx.doi.org/10.3390/app12157786.

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The rockburst simulation test is conducted by utilizing a mineral-containing marble specimen. The loading condition is set to the three directions, each loading on five surfaces except for a single free surface. The whole test procedure is monitored in real time by using a PCI-II acoustic emission monitoring system and a high-speed camera. According to the test outcomes, rockburst is a process in which energy is rapidly released from the free surface. Rock block and rock plate are buckled and ejected from the free surface and a severe rockburst process is accompanied by spray rock powder. An explosion sound can be heard during the process, which can be analyzed by signal processing techniques. The failure mode of the specimen is a splitting-shearing composite failure, and the free surface becomes a rockburst destruction surface. A V-type rockburst pit is formed in the ejection area. The effective acoustic emission signal of the whole test process is decomposed and reconstructed using five-layer wavelets to produce six frequency band sub-signals. In addition, the wavelet energy and its energy distribution coefficients are assessed for various frequency bands, and the proportion of each dominant frequency band within each period is computed. Finally, it was found that the dominant frequency band is 125~250 kHz, while the suboptimal frequency band is 250~500 kHz. The succeeding features are noticed to be used as predicted features for the rockburst disaster. Namely, acoustic emission signals arise in large numbers and the energy distribution coefficient of the dominant frequency band concentrates above 0.4. The proportion of dominant frequency band appears in continuous valley type and keeps below 80%, while the proportion of suboptimal frequency band appears in continuous peak type and keeps above 20%.

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48

Mortazavi, Ali, and Hadi Atapour. "An experimental study of stress changes induced by reservoir depletion under true triaxial stress loading conditions." Journal of Petroleum Science and Engineering 171 (December 2018): 1366–77. http://dx.doi.org/10.1016/j.petrol.2018.08.047.

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49

Xiao, Fan, Deyi Jiang, Fei Wu, Quanle Zou, Jie Chen, Bo Chen, and Zhongguang Sun. "Effects of prior cyclic loading damage on failure characteristics of sandstone under true-triaxial unloading conditions." International Journal of Rock Mechanics and Mining Sciences 132 (August 2020): 104379. http://dx.doi.org/10.1016/j.ijrmms.2020.104379.

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50

Akdag, Selahattin, Murat Karakus, Abbas Taheri, Giang Nguyen, and He Manchao. "Effects of Thermal Damage on Strain Burst Mechanism for Brittle Rocks Under True-Triaxial Loading Conditions." Rock Mechanics and Rock Engineering 51, no. 6 (February 17, 2018): 1657–82. http://dx.doi.org/10.1007/s00603-018-1415-3.

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