scholarly journals Triaxial Creep Behavior of Red Sandstone in Freeze-Thaw Environments

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Yongjun Song ◽  
Yongxin Che ◽  
Leitao Zhang ◽  
Jianxi Ren ◽  
Shaojie Chen ◽  
...  
Keyword(s):  
Stress Level ◽  
Creep Deformation ◽  
Transverse Shear ◽  
Shear Plane ◽  
Confining Pressure ◽  
Term Strength ◽  
Red Sandstone ◽  
Freeze Thaw ◽  
Viscoelastic Strain

To investigate the time-dependent mechanical properties of rock masses in cold regions under the effects of freeze-thaw cycling and long-term loading, triaxial multilevel loading and unloading creep tests were performed on saturated red sandstone samples subjected to different numbers of freeze-thaw cycles. The effects of freeze-thaw cycles and confining pressure on the creep properties, long-term strength, and creep failure mode of the rock were analyzed. The effect of freeze-thaw cycles on the microstructure of the rock was analyzed using scanning electron microscopy. The results showed that as the number of freeze-thaw cycles increased, the rock particle boundaries became more distinct, and more pores formed. The effect of freeze-thaw cycles on the creep deformation of red sandstone was related to the loading stress level. At low stress levels, the rock viscoelastic strain increased gradually and almost linearly with an increasing number of freeze-thaw cycles; in contrast, at high stress levels, the rock viscoelastic strain increased nonlinearly. The viscoplastic strain increased almost linearly with increasing freeze-thaw cycles. The fourth loading stress level (70% σ c ) corresponded to the transition of the creep deformation of the red sandstone. When the confining pressure was low, a higher stress level caused the confining pressure to have a more significant effect on the creep strain. However, as the confining pressure continued to increase, the effect of the confining pressure on the creep strain eventually disappeared. The long-term strength of the red sandstone decreased approximately linearly with an increase in the number of freeze-thaw cycles. When the number of freeze-thaw cycles and the confining pressure were high, the rock samples formed a transverse shear plane and were more fragmented than those without a transverse shear plane. These results provide a reference for construction in rock mass engineering and long-term stability analysis in cold regions.

Analysis of Creep Characteristics of Shallow Mined-Out Areas Roof under Low Stress Conditions

2011 ◽  
Vol 105-107 ◽  
pp. 832-836 ◽  
Author(s):  
Shu Ren Wang ◽  
Hui Hui Jia
Keyword(s):  
Creep Deformation ◽  
Thick Plate ◽  
Plate Theory ◽  
Technical Problem ◽  
Stress Conditions ◽  
Creep Model ◽  
Term Strength ◽  
Creep Characteristics ◽  
Over Time

Under low stress conditions, when the load exerting on the mined-out areas roof is less than the rock long-term strength, the rock roof will generate some creep deformation. In order to prevent the roof of the mined-out areas suddenly collapse, and to ensure the operator and construction equipment above the mined-out areas safety, it is an important security technical problem to reveal the creep characteristics of the shallow mined-out areas roof. Taking the mined-out areas of Antaibao Surface Mine as background, considering the rheological properties of rock roof, and assuming the roof was a rectangular thick plate, the creep characteristics of mined-out areas roof were analysed by applying the thick plate theory and Kelvin creep model. The regression equation of the roof deflection increment over time was given, and the creep characteristics of the shallow mined-out areas roof were revealed also.

On the Interrupted Creep Test Under Low Stress Levels for the Power Law Parameter Extraction

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Bin Yang ◽  
Fu-Zhen Xuan ◽  
Wen-Chun Jiang
Keyword(s):  
Creep Strain ◽  
Stress Level ◽  
Creep Test ◽  
Creep Deformation ◽  
Parameter Extraction ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Creep Stage ◽  
Strain Data

Abstract Low stress interrupted creep test, as an interim compromise, can provide essential data for creep deformation design. However, there are no clear guidelines on the characterization of the terminating time for interrupted low-stress creep test. To obtain a suitable terminating time in terms of economy and effectiveness, long-term creep strain data of 9%Cr steels are collected from literatures and their creep deformation characterization is analyzed. First, the variations of normalized time and strain of each creep stage with the stress level are discussed. Then, the effect of the terminating time on final fitted results of Norton–Bailey equation is estimated. Third, the relationship between demarcation points at different creep stages and minimum/steady-state creep rate is analyzed. The results indicate that when the creep rupture life is considered as an important factor for creep design, the tertiary creep stage is of greatest significance due to the largest life fraction and creep strain fraction at low stress level. However, the primary and secondary creep stages are of great significance for design due to their larger contribution to 1% limited creep strain. And the long-term secondary creep data could be extrapolated by combining the primary creep strain data obtained from interrupted creep tests with the time to onset of tertiary creep derived from a similar Monkman–Grant relationship.

scholarly journals Applicability of single sample method to test strength parameters of sandstone

2021 ◽  
Vol 2076 (1) ◽  
pp. 012019
Author(s):  
Shaoan Li ◽  
Wenxia Li ◽  
Yunlei Hu ◽  
Tao Zhang ◽  
Xiangchao Shi
Keyword(s):  
Yield Point ◽  
Confining Pressure ◽  
Single Sample ◽  
Term Strength ◽  
Strength Parameters ◽  
Loading Tests ◽  
Sample Method ◽  
Compressive Tests ◽  
Multistage Loading

Abstract The single sample method allows the mechanical parameters of rocks to be obtained with very few rock samples; however, the method has not been widely used. This is mainly because the yield point of the single sample method is more difficult to control than the conventional triaxial compressive test and the effect of the different control methods on the measured data is not well understood. The single sample method obtains the strength parameters of the rock by loading a single rock sample with multiple stages of confining pressure. Multistage loading tests are divided into peak strength control and long-term strength control according to yield point control. In this study, multistage loading tests of sandstone were carried out to obtain strength parameters using long-term strength control. The results show that sandstones undergo seriously brittle damage in conventional triaxial compressive tests. Although the sandstones have been rigorously selected, they still vary considerably, and long-term strength points are more difficult to control. The error of strength parameters of sandstone obtained using the single sample method may exceed 20% compared to those obtained by conventional triaxial compressive tests. So this method must be used with caution for sandstones.

scholarly journals A Fractional Creep Constitutive Model for Frozen Soil in Consideration of the Strengthening and Weakening Effects

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Feng Hou ◽  
Quanming Li ◽  
Enlong Liu ◽  
Cheng Zhou ◽  
Mengke Liao ◽  
...  
Keyword(s):  
Shear Stress ◽  
Constitutive Model ◽  
Test Specimen ◽  
Confining Pressure ◽  
Frozen Soil ◽  
Strengthening Effect ◽  
Term Strength ◽  
Test Results ◽  
Creep Constitutive Model

The triaxial creep tests of frozen silty clay mixed with sands were performed under different pressures, and the test results demonstrated that, under the low confining pressure, when the shear stress is lower than the long-term strength, the test specimen exhibits an attenuation creep because the strengthening effect is greater than the weakening effect. When the shear stress is higher than the long-term strength, the test specimen exhibits a nonattenuation creep due to the level of the strengthening and weakening effects change in different stages. As the confining pressure increases, the test specimens only exhibit an attenuation creep because of the enhancing strengthening effect. Both the hardening parameter and the damage variable were introduced to describe the strengthening and weakening effects, respectively, and a new creep constitutive model for frozen soil considering these effects was put forward based on the theory of elastoviscoplastic and the fractional derivative. Finally, the model parameters were analyzed and their determination method was also provided to reveal the trend of parameters according to the triaxial test results. The calculated results of the constitutive model show that the proposed model can describe the whole creep process of frozen soil well.

Experimental Research on Coupling of Swelling Rock between Swelling and Creep

2013 ◽  
Vol 353-356 ◽  
pp. 293-302
Author(s):  
Qiu Yan Fan ◽  
Mei Qian Wang ◽  
Xian Li ◽  
Bo Zhang
Keyword(s):  
Creep Deformation ◽  
Residual Deformation ◽  
Swelling Pressure ◽  
Initial Water Content ◽  
Term Strength ◽  
Compression Tests ◽  
Initial Water ◽  
Multi Stage ◽  
Swelling Rock

Swelling rock has the properties of swelling and creep. Researches on coupling between swelling and creep have not yet been carried out. The expansive Paleogene mudstone is used to laboratory uniaxial compression tests, to find the coupling regularity between swelling and creep under different initial water contents, influent modes and loading methods. For coupling, the creep curves show similar characteristic of non-coupling. The creep deformation increases obviously and the long-term strength decreases comparing with non-coupling. With increasing initial water content, the creep deformation increases for coupling. The creep deformation increases with the enlargement of water-absorption area during the coupling creep. For single-stage and multi-stage loading, the creep regularity is similar to non-coupling. The sample will have a permanent residual deformation when unloaded at the second stable creep stage. The long-term strength of swelling rock is greater than the swelling pressure and the long-term strength is lower than that of non-coupling.

scholarly journals Study on Mechanical Properties and Damage Characteristics of Red Sandstone under Freeze-thaw and Load

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Lei Shi ◽  
Yang Liu ◽  
Xiangzhen Meng ◽  
Huimei Zhang
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Damage Variable ◽  
Mechanical Parameters ◽  
Compression Tests ◽  
Internal Damage ◽  
Red Sandstone ◽  
Freeze Thaw ◽  
Total Damage

To analyze the effects of freeze-thaw cycles and confining pressure on the mechanical properties of red sandstone, through freeze-thaw cycles and triaxial compression tests, full stress-strain curves of different freeze-thaw cycles and different confining pressures were obtained. The degradation degree of red sandstone was quantitatively considered from different mechanical parameters of ultimate stress, elastic modulus, and Poisson’s ratio. Based on summarizing the characteristics of rock under freeze-thaw and load, the total damage variable of rock was determined by the reasonable measurement of freeze-thaw damage variable and load damage variable, and a damage constitutive model under freeze-thaw and load was established. The research showed that the freeze-thaw cycles aggravate the degree of rock damage deterioration, the rock stiffness and strength were reduced, and the characteristics of plastic deformation and ductile failure were more obvious. The confining pressure inhibited red sandstone internal damage, and with the increase of confining pressure, the stiffness and strength and the plastic characteristics were increased. In the overall trend, the mechanical parameters had different sensitivity to the degradation effect of freeze-thaw cycles and confining pressure. Regardless of the increase in the number of freeze-thaw cycles or confining pressure, the strain softening modulus tended to decrease gradually, and red sandstone plastic damage became more obvious after the stress peak. The total damage evolution path of red sandstone reflected the nonlinear influence of freeze-thaw and load on the total damage propagation. The research results provide theoretical support for the improvement of the technology of the effluent coal rock in Balasu Coal Mine.

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

Geofluids ◽  
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.

Experimental study on creep deformation and long-term strength of unloading-fractured marble

2015 ◽  
Vol 19 (sup1) ◽  
pp. s97-s107 ◽  
Author(s):  
Liu Jian-feng ◽  
Wang Lu ◽  
Pei Jian-liang ◽  
Zheng Lu ◽  
Bian Yu
Keyword(s):  
Experimental Study ◽  
Creep Deformation ◽  
Term Strength

Subcritical Crack Growth and Long-Term Strength in Rock and High-Strength and Ultra Low-Permeability Concrete

2009 ◽  
Vol 58 (6) ◽  
pp. 525-532 ◽  
Author(s):  
Yoshitaka NARA ◽  
Masafumi TAKADA ◽  
Daisuke MORI ◽  
Hitoshi OWADA ◽  
Tetsuro YONEDA ◽  
...  
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
High Strength ◽  
Low Permeability ◽  
Term Strength

Long-term strength of reinforcing steel 22H2G2АYu in case of corrosion cracking test in boiling nitrate solution

2019 ◽  
pp. 33-39
Author(s):  
N. N. Sergeev ◽  
◽  
S. N. Kutepov ◽  
A. N. Sergeev ◽  
A. G. Kolmakov ◽  
...  
Keyword(s):  
Nitrate Solution ◽  
Corrosion Cracking ◽  
Term Strength ◽  
Reinforcing Steel
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