Applicability of single sample method to test strength parameters of sandstone

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.

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

Advances in Materials Science and Engineering ◽

10.1155/2016/5740292 ◽

2016 ◽

Vol 2016 ◽

pp. 1-12 ◽

Cited By ~ 4

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.

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Triaxial Creep Behavior of Red Sandstone in Freeze-Thaw Environments

Geofluids ◽

10.1155/2020/6641377 ◽

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.

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