The Uniaxial Creep Characteristics of Red Sandstone under Dry-Wet Cycles

Water is one of the most important factors that affect the long-term stability of geotechnical engineering structures. Rainfall often results in periodic changes in the water content in underground rock, which is subjected to alternating dry-wet cycles. In this paper, in order to study the short-term and long-term mechanical properties of red sandstone under these dry-wet cycles, a series of uniaxial compressive strength (UCS) tests and multistage creep tests have been carried out on specimens of red sandstone after being treated to different numbers of dry-wet cycles. A scanning electron microscope (SEM) was used to image the different groups of specimens. The test results have shown that the peak strength and the elastic modulus of the red sandstone decreased as the number of dry-wet cycles increased. It is worth noting that the first immersion of the specimens decreased their strength the most, and the negative logarithmic function was able to better reflect the peak strength of the red sandstone and the variation of its elastic modulus in relation to the number of dry-wet cycles. The results of the creep tests have shown that the instantaneous strain and creep strain of the sandstone increased significantly with the increase of the number of dry-wet cycles. A linear function and a negative logarithmic function can be used to describe the instantaneous strain and the creep strain, respectively. The creep duration of the red sandstone in its failure stage decreased with the increase of the number of dry-wet cycles, and the creep rate increased with the increase of the number of dry-wet cycles. Lastly, the failure modes of the red sandstone were observed; the results showed that the angle between the main crack and the axis of creep failure gradually increased with the increase of the number of dry-wet cycles and the angle of the internal friction and the cohesion decreased. In addition, the failure mode of the specimens changed from tensile failure to shear failure. The microstructure of the sandstone showed that the surface of the specimen changed from being compact to being loose, and the mineral particles in the specimen changed from being spherical to being flat and curly; this led to a decrease in the macroscopic mechanical parameters of the sandstone.

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Creep damage behavior of red sandstone after high temperature

10.22541/au.162108952.29835546/v1 ◽

2021 ◽

Author(s):

Xiaokang Pan ◽

Filippo Berto ◽

Xiaoping Zhou

Keyword(s):

High Temperature ◽

Uniaxial Compression ◽

Deformation Modulus ◽

Creep Damage ◽

Viscosity Coefficient ◽

Creep Tests ◽

Red Sandstone ◽

Instantaneous Strain ◽

Treated Sample ◽

Instantaneous Deformation

This work discusses the results from tests conducted to investigate the uniaxial compression and creep behavior of red sandstone. The original untreated sample and the 800 ℃ treated sample have been selected to carry out the experiments. It has been found that high temperature has obvious influence on the mechanical properties of red sandstone. The relationship between creep strain and instantaneous strain, as well as instantaneous deformation modulus and creep viscosity coefficient have been analyzed. It has been found that high temperature reduces the ability of red sandstone to resist instantaneous deformation and creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests, providing a powerful means for damage evolution analysis of red sandstone.

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Effects of moisture content and temperature on wood creep

Holzforschung ◽

10.1515/hf-2018-0056 ◽

2018 ◽

Vol 72 (12) ◽

pp. 1071-1078 ◽

Cited By ~ 4

Author(s):

Tai-Yun Hsieh ◽

Feng-Cheng Chang

Keyword(s):

Moisture Content ◽

Creep Strain ◽

Superposition Principle ◽

Japanese Cedar ◽

Creep Tests ◽

Instantaneous Strain ◽

Proposed Model ◽

Time Temperature Superposition Principle ◽

Term Creep ◽

Short Term Creep

AbstractThe effects of moisture content (MC) and temperature (T) on the creep of Japanese cedar were investigated via a series of short-term creep tests, while MC had a higher effect than T, desorption of water caused more deformation. The results were separated into two distinct groups with MCs higher or lower than the equilibrium moisture content (EMC) and it was found that the mechano-sorptive effect is time-independent. The total creep strain of wood was explained by a model considering the instantaneous strain, creep strain and strain induced by the mechano-sorptive effect. The proposed model is in agreement with the creep master curves based on the time-temperature superposition principle (tTSP).

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Creep Strain Analysis and an Improved Creep Model of Granite Based on the Ratio of Deviatoric Stress-Peak Strength under Different Confining Pressures

10.21203/rs.3.rs-317168/v1 ◽

2021 ◽

Author(s):

Li Qian ◽

Jianhai Zhang ◽

Xianliang Wang ◽

Yonghong Li ◽

Ru Zhang ◽

...

Keyword(s):

Elastic Modulus ◽

Creep Behavior ◽

Viscosity Coefficient ◽

Deviatoric Stress ◽

Peak Strength ◽

Creep Model ◽

Secondary Creep ◽

Creep Tests ◽

Underground Powerhouse ◽

Confining Pressures

Abstract Creep refers to the deformation of rock with time under long-term applied stress, which occur in most underground engineering. The creep behavior of granite in Shuang jiangkou underground powerhouse in Western Sichuan Province, China, was studied by creep tests. Based on test results, a new parameter DPR, the ratio of deviatoric stress to peak strength, is proposed. DPR is found to be a key parameter to describe creep parameters such as instantaneous elastic modulus, creep elastic modulus, and viscosity coefficient of rock under different confining pressures. Creep tests show that instantaneous elastic modulus increases with the increase of DPR. Creep elastic modulus increases when DPR changes from 0.54 to 0.7004, but decreases when DPR is from 0.7004 to 0.88, indicating fractures in rock closes firstly and then new fractures are generated. The viscosity coefficient of the rock increases first and then decreases with the increase of DPR, and when DPR = 0.7171, viscosity coefficient is maximum, indicating the time for rock to reach stability is the longest in creep tests. By introducing DPR and confining pressure into creep model, which interconnect creep parameters in a unified expression, an improved generalized Kelvin creep model is proposed which can accurately describe the primary and the secondary creep behavior of granite under given deviatoric stresses and confining pressures.

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Creep Characteristics of Different Saturated States of Red Sandstone after Freeze-Thaw Cycles

Geofluids ◽

10.1155/2021/6622380 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Yongxin Che ◽

Yongjun Song ◽

Jianxi Ren ◽

Jiaxing Chen ◽

Xixi Guo ◽

...

Keyword(s):

Mechanical Characteristics ◽

Creep Failure ◽

Creep Tests ◽

Red Sandstone ◽

Freeze Thaw ◽

Sem Image ◽

In Series ◽

Distribution Shifts ◽

The Right

To investigate the creep mechanical characteristics of rocks in different saturated states after freeze-thaw cycles, samples with different saturations (30%, 50%, 70%, 90%, and 100%) were selected for nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and uniaxial compression creep tests. The internal microscopic damage of the rock sample and mechanical characteristics under long-term loading are analyzed after the action of freeze-thaw cycles. The test results show that, as the saturation increases, the T2 spectrum distribution shifts to the right. The spectrum area gradually increases as the porosity increases. The critical saturation of freeze-thaw damage occurs when the saturation increases from 70% to 90%. It can be seen from the SEM image that the number of pores inside the rock samples gradually increases with increases in saturation, leading to the appearance of cracks. Under long-term loading, the saturation has a significant influence on the time-efficiency characteristics of sandstone freeze-thaw. As the saturation increases, the creep deformation gradually increases. After reaching 70%, the axial creep strain increases significantly. The rate of creep is accelerated, the creep failure stress is reduced, and the creep time under the last level of stress is significantly increased. A modified viscous-plastic body is connected in series to the basic Burgers model, the freeze-thaw-damage viscous element is introduced, and the creep parameters are fitted using test data. The results will provide a reference for long-term antifreeze design for rock engineering in cold areas.

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The Conventional Triaxial Compressive Test of Plain Reactive Powder Concrete

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.670-671.401 ◽

2014 ◽

Vol 670-671 ◽

pp. 401-406

Author(s):

Xiao Fei Wang ◽

Yang Ping Wang

Keyword(s):

Elastic Modulus ◽

Failure Modes ◽

Shear Failure ◽

Poisson Ratio ◽

Confining Pressure ◽

Peak Strength ◽

Reactive Powder Concrete ◽

Peak Strain ◽

Confining Pressures ◽

Reactive Powder

Through the conventional triaxial test about plain reactive powder concrete under different confining pressures at 0Mpa, 25 Mpa,50 Mpa and 75 Mpa, this paper obtained the stress-strain curves in axial direction and radial direction of plain reactive powder concrete under different confining pressures, compared and analyzed the effects of confining pressures on peak strength, peak strain, Elastic modulus, Poisson ratio and failure modes of plain reactive power concrete also. The results showed that peak strength increases with the increase of confining pressure, when confining pressure increases from 0Mpa to 25Mpa, the peak strength increases most rapidly. The results also showed that peak strain increases linearly with the increase of confining pressure, when confining pressure increase from 0Mpa to 75Mpa gradually, the peak strain increases from 0.2 percent to 0.93 percent, meanwhile Poisson ratio increase with the increase of confining pressures, yet Elastic modulus changes slight at different confining pressures, failure modes of plain reactive powder concrete at different confining pressures exhibit different modes, when confining pressure is 0Mpa, failure mode presents as splitting failure, shear failure mode at 25Mpa, while shear failure merge local crushing at 50MPa and 75MPa.

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Experimental Investigations on Creep Behavior of Coal under Combined Compression and Shear Loading

Geofluids ◽

10.1155/2021/9965228 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Rongbin Hou ◽

Leige Xu ◽

Duoxin Zhang ◽

Yanke Shi ◽

Luyang Shi

Keyword(s):

Inclination Angle ◽

Creep Test ◽

Creep Behavior ◽

Shear Loading ◽

Peak Strength ◽

Term Strength ◽

Creep Tests ◽

Inclination Angles ◽

Pure Compression

The creep behavior of rock has received much attention for analyzing the long-term response and stability of underground rock engineering structures. Numerous studies have been carried out on the creep properties of various rocks under pure compression conditions. However, little attention has been paid to the creep behavior of rocks in a combined compression-shear loading state. In this work, a novel combined compression and shear test (C-CAST) system was used to carry out inclined uniaxial compression tests and creep tests for various inclination angles (0°, 5°, 10°, and 15°). The results revealed that the peak strength of the coal decreased with the inclination angle of the specimen, which could provide the basis for setting up a creep test scheme. Multistage compression-shear creep tests were carried out on specimens with different inclination angles. Based on the analysis of the creep test data, the creep behavior of the coal in a combined compression-shear state was studied. It was found that the specimen inclination affected the time-dependent deformation, long-term strength (LTS), and time to failure. Compared with the specimen under pure compression, the inclination specimens tend to produce large shear strain with time, while they were more prone to shear failure. The reduction of the long-term strength was closely associated with the increase of the specimen inclination angle when the angle was more than 5°. Moreover, the ratio of the peak strength to the LTS was not affected by the specimen inclination, which is considered an inherent characteristic. We anticipate that the results obtained will assist in pillar design and long-term stability analysis.

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Review of the Durability of Polymer Electrolyte Membrane Fuel Cell in Long-Term Operation: Main Influencing Parameters and Testing Protocols

Energies ◽

10.3390/en14134048 ◽

2021 ◽

Vol 14 (13) ◽

pp. 4048

Author(s):

Huu Linh Nguyen ◽

Jeasu Han ◽

Xuan Linh Nguyen ◽

Sangseok Yu ◽

Young-Mo Goo ◽

...

Keyword(s):

Fuel Cell ◽

Polymer Electrolyte ◽

Failure Modes ◽

Polymer Electrolyte Membrane ◽

Durability Test ◽

Term Operation ◽

Electrolyte Membrane ◽

Transportation Applications ◽

Testing Protocols

Durability is the most pressing issue preventing the efficient commercialization of polymer electrolyte membrane fuel cell (PEMFC) stationary and transportation applications. A big barrier to overcoming the durability limitations is gaining a better understanding of failure modes for user profiles. In addition, durability test protocols for determining the lifetime of PEMFCs are important factors in the development of the technology. These methods are designed to gather enough data about the cell/stack to understand its efficiency and durability without causing it to fail. They also provide some indication of the cell/stack’s age in terms of changes in performance over time. Based on a study of the literature, the fundamental factors influencing PEMFC long-term durability and the durability test protocols for both PEMFC stationary and transportation applications were discussed and outlined in depth in this review. This brief analysis should provide engineers and researchers with a fast overview as well as a useful toolbox for investigating PEMFC durability issues.

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Coulomb stress analysis for several filling and operational scenarios at the Grand Ethiopian Renaissance Dam impoundment

Environmental Earth Sciences ◽

10.1007/s12665-021-09591-w ◽

2021 ◽

Vol 80 (7) ◽

Author(s):

Austin Madson ◽

Yongwei Sheng

Keyword(s):

Coulomb Stress ◽

Engineering Structures ◽

Main Driver ◽

Potential Reservoir ◽

Coulomb Stress Analysis ◽

Storage Change ◽

Total Maximum ◽

Western Ethiopia ◽

Maximum Stresses

AbstractIncreased demand for power generation coupled with changing seasonal water uncertainty has caused a worldwide increase in the construction of large hydrologic engineering structures. That said, the soon-to-be-completed Grand Ethiopian Renaissance Dam (GERD) will impound the Blue Nile River in Western Ethiopia and its reservoir will encompass ~ 1763 km2 and store ~ 67 Gt (km3) of surface water. The impoundment will undergo maximum seasonal load changes of ~ 28 to ~ 36 Gt during projected seasonal hydroelectric operations. The GERD impoundment will cause significant subsurficial stresses, and could possibly trigger seismicity in the region. This study examines Coulomb stress and hydrologic load centroid movements for several GERD impoundment and operational scenarios. The maximum subsurficial Coulomb stress applied on optimally oriented fault planes from the full impoundment is ~ 186 kPa and over 30% of our model domain incurs Coulomb stresses ≥ 10 kPa, regardless of the impoundment period length. The main driver behind Coulomb stress and load centroid motion during impoundment is the annual, accumulated daily reservoir storage change. The maximum Coulomb stresses from the highest amplitude season of five long-term operational scenarios are around 36, 33, 29, 41, and 24% of the total maximum stresses from the entire GERD impoundment. Variations in annual Coulomb stresses during modeled GERD operations are attributed to the seasonal load per unit area, and partially to the initial seasonal water level. The spatial patterns and amplitudes of these stress tensors are closely linked to both the size and timing of GERD inflow/outflow rates, and an improved understanding of the magnitude and extent of these stresses provides useful information to water managers to better understand potential reservoir triggered seismic events from several different operational and impoundment strategies.

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