Nonlinear Elasto-Visco-Plastic Creep Behavior and New Creep Damage Model of Dolomitic Limestone Subjected to Cyclic Incremental Loading and Unloading

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.

A new shear creep damage model for rock masses after considering initial damage

“…Rocks naturally form pores, fissures, cracks, dislocations and other defects at different stages of time during their long geological history, thereby leading to uneven initial damage in rocks [36][37][38][39]. Current research on creep damage theory in rocks generally assumes that the rock is in an undamaged state at the initial creep stage (t = 0) [40][41][42].…”

Emphasizing the Creep Damage Constitutive Model of Hydro-Mechanical Properties of Rocks: A Case Study of Granite Gneiss

“…In Equation (8), by describing the time-dependent damage variable in the creep process, an elastoplastic creep damage constitutive model that would describe the creep mechanical properties of rock can be established.…”

“…Integrating the basic components, in series or parallel, which is a composite component model that can reflect various creep characteristics can be obtained. The research on constitutive models of rock elements mainly focuses on the following three aspects: (1) introducing new nonlinear components to establish a new constitutive model of the components, (2) taking the parameters in the model as non-stationary values, and (3) introducing new methods and theories to establish the model [8][9][10]. In recent years, more and more experts and scholars have conducted in-depth research on the nonlinear creep mechanical behavior of rocks based on the advantages of component models, and established many new nonlinear constitutive models using methods such as substitution and addition [11,12].…”

Study on Experimental and Constitutive Model of Granite Gneiss under Hydro-Mechanical Properties

“…The central research methods include applying empirical equations to test results directly, parallel connections of assorted components, as well as adding nonlinear terms. In view of the elastic-plastic theoretical framework, there were three sorts of rock constitutive models [21][22][23]. By simulating the influence of seepage in rocks on their deformation behavior under stress, the permeate influence on the rock's inner stress field can effectively be achieved.…”