Journal
ROCK MECHANICS AND ROCK ENGINEERING
Volume 50, Issue 6, Pages 1409-1424Publisher
SPRINGER WIEN
DOI: 10.1007/s00603-017-1187-1
Keywords
Creep behavior; Creep test; Multi-level loading and unloading cycles; Maokou limestone
Funding
- National Natural Science Foundation of China [51274097, 51434006, 51374104]
- Natural Science Foundation of Hunan province [2015JJ2067]
- Shanghai Thousand Talents Program
- Open Projects of State Key Laboratory of Coal Resources and Safe Mining, CUMT [SKLCRSM16KF12]
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A series of triaxial creep tests were carried out on intact and cracked Maokou limestone specimens under multi-level loading and unloading cycles. A new data processing algorithm is proposed to analyze the experimental data and divide the total strain into instantaneous and creep strains, with the instantaneous strain consisting of instantaneous elastic and plastic strains and the creep strain consisting of viscoelastic and visco-plastic strains. The results show that the viscoelastic strain converges to a certain value with time, but the visco-plastic strain keeps increasing with time, although both tend to increase with higher deviatoric stress. The ratio of the visco-plastic strain to the total creep strain also tends to increase when the deviatoric stress is higher. The steady-state creep strain rate increases with higher deviatoric stress or lower confining pressure, and the relation between the steady-state creep strain rate and the deviatoric stress can be well described by an exponential expression. The results also show that the preexisting cracks in the limestone have a great effect on its creep properties. At the same confining pressure and deviatoric stress, the cracked limestone shows larger instantaneous and creep strains (especially visco-plastic strains), longer duration of primary creep, and a higher steady-state creep strain rate than the intact limestone.
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