Abstract
For many rock engineering projects, the stress of surrounding rocks is constantly increasing and decreasing during excavating progress and the long-term operation stage. Herein, the triaxial creep behavior of dolomitic limestone subjected to cyclic incremental loading and unloading was probed using an advanced rock mechanics testing system (i.e., MTS815.04). Then, the instantaneous elastic strain, instantaneous plastic strain, visco-elastic strain, and visco-plastic strain components were separated from the total strain curve, and evolutions of these different types of strain with deviatoric stress increment were analyzed. Furthermore, a damage variable considering the proportion of irrecoverable plastic strain to the total strain was introduced, and a new nonlinear multi-element creep model was established by connecting the newly proposed damage viscous body in series with the Hookean substance, St. Venant body, and Kelvin element. The parameters of this new model were analyzed. The findings are listed as follows: (1) When the deviatoric stress is not more than 75% of the compressive strength, only instantaneous deformation, transient creep, and steady-state creep deformation occur, rock deformation is mainly characterized by the instantaneous strain, whereas the irrecoverable instantaneous plastic strain accounts for 38.02–60.27% of the total instantaneous strain; (2) Greater deviatoric stress corresponds to more obvious creep deformation. The visco-elastic strain increases linearly with the increase of deviatoric stress, especially the irrecoverable visco-plastic strain increases exponentially with deviatoric stress increment, and finally leads to accelerated creep and delayed failure of the sample; (3) Based on the experimental data, the proposed nonlinear creep model is verified to describe the full creep stage perfectly, particularly the tertiary creep stage. These results could deepen our understanding of the elasto-visco-plastic deformation behavior of dolomitic limestone and have theoretical and practical significance for the safe excavation and long-term stability of underground rock engineering.
Highlights
The triaxial compression creep behaviors of dolomitic limestone subjected to cyclic incremental loading and unloading manifest that the instantaneous deformation occurs firstly during every deviatoric stress level and creep deformation occurs
When the loading deviatoric stress is not more than 75% of the conventional triaxial compression strength, only transient creep stage and steady-state creep stage occur successively
The separation of elasto-visco-plastic strain component shows that rock deformation is mainly characterized by instantaneous strain while the deviatoric stress is not more than 75% of the conventional compressive strength, especially the irrecoverable instantaneous plastic strain accounts for 37.97–60.27% of total instantaneous strain and should not be ignored during rock engineering design
Summary
Many scholars have carried out extensive research on creep mechanical behaviors of different types of rocks. Maranini and Brignoli [12], Yang et al [11], Fujii et al [13], and Wang et al [14] have obtained a lot of research achievements in uniaxial and triaxial compression creep characteristics of soft rocks such as limestone, salt, clasticrock, weathered sandstone, and coal rock. The creep mechanical properties of hard rocks, such as greenschist [15], diabase [16], marble [17], and red sandstone [18] under stepwise
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