Experimental investigations on creep behavior of fractured granite have been performed under multi-step stresses. The significant stress effect on the creep strain rate is presented. A coupling damage of the initial macroscopic damage of fractured granite and the microscopic damage induced by external load is deduced. A damage-mechanism-based creep model for fractured granite has been proposed by introducing the damage evolution in the constitutive relations. The model parameters are determined by fitting the experimental results of the time-dependent deformation of fractured granite. It is indicated that the creep constitutive model proposed can provide a precise description of the full creep process in fractured granite under different stresses. The Burgers model is indicated to be a special case of the damage-mechanism-based creep model.
Deep geological disposal is considered to be a feasible and safe option to deal with the high-level radioactive waste (HLW). The deep geological repository (DGR) is consequently considered to be built in many countries. Meanwhile, a number of underground research laboratories (URLs) for demonstrating the long-term safety of DGRs are under construction around the world. In order to ensure the long-term stability and safety of DGRs and URLs, a good understanding and the reliable modeling method for the time-dependent behavior of host rock is essential.
During several decades many efforts have been directed toward the study on creep constitutive model. The component model has been widely studied and applied because of its intuitive concept and clear physical meaning (e.g., reviews by Tomanovic 2006, Sterpi & Gioda 2009, Fahimifar et al. 2015, Aditya et al. 2018). Zhou et al. (2011, 2012) proposed a fractional derivative model by replacing the Newtonian dashpot with the variable-viscosity Abel dashpot in Nishihara model. Based on the Burger's body, Fahimifar et al. (2010) presented a new formulation to determine the wall displacement and convergence of tunnel. Zhang et al. (2019) established a nonlinear creep damage model by introducing the internal variables into the creep model. Cao et al. (2020) gave a unified creep model to describe the typical creep behavior stages for rock under multiple stress levels based on the time-hardening theory and the damage theory. However, most of these improved models are complex with many components and complicated combination forms, or in the form of implicit functions and the explicit expression cannot be derived, which may bring many difficulties to the engineering application. In this paper, the experimental data of fractured granite samples in creep test is first analyzed. On this basis, a new creep model for fractured granite is formulated through introduction of damage variable in the constitutive relations. The model parameters are determined by fitting the experimental curves of fractured granite samples.
