# Creep Model of Weakly Cemented Soft Rock Considering Damage and Secondary Development in FLAC3D
## 1 Introduction  
Weakly cemented soft rock exhibits significant rheological behavior under mining-induced stress due to its unique characteristics, including weak cementation, a highly porous structure, and the presence of hydrolysate minerals [1, 2]. This rheological evolution not only results in nonlinear increases in the deformation of surrounding rock in roadways but also leads to major engineering challenges, such as the instability of support structures and coal-rock-gas outbursts [3, 4, 5, 6, 7]. Given its crucial role in controlling the long-term stability of underground openings, the rheological constitutive characterization of weaklycemented soft rock has become a central focus in rock mechanics research. Developing a rational creep model is essential for understanding rheological failure mechanisms and for guiding the design of effective roadway support systems [8; 9; 10]. To summarize recent research progress, [PERSON] et al. [11] and [PERSON] et al. [12] conducted comprehensive reviews of existing creep models, offering important theoretical insights for the development of new constitutive formulations. Among the various models, the Nishihara model has been widely adopted for its ability to describe the full creep process in soft rock [13; 14; 15; 16]. To improve its applicability under diverse conditions, researchers have introduced several enhancements. For example, [PERSON] et al. [17] proposed a modified Nishihara model incorporating a novel dashpot element to characterize accelerated creep behavior and to effectively capture the mechanical response of sandstone under varying moisture conditions. [PERSON] et al. [18], based on creep tests on rock salt under different confining pressures and axial stresses, proposed a viscoplastic damage model incorporating long-term strength and time-dependent behavior, resulting in a six-element nonlinear creep model capable of accurately reproducing creep curves. [PERSON] et al. [19] introduced a strain-triggered inertial element into the model to represent secondary accelerated creep, enabling a mathematical description of the full creep process from primary decay to steady-state and accelerated creep. [PERSON] et al. [20] replaced the Newtonian dashpot in the traditional Nishihara model with a fractional-order Abel dashpot and proposed a time-fractional derivative-based creep model, including an analytical solution. [PERSON] et al. [21] developed a four-element fractional creep model for weakly cemented soft rock by integrating creep test results with fractional calculus theory and Abel dashpots, effectively describing its three-stage creep behavior. Numerical simulation software has also become an essential tool due to its efficiency and capability to replicate complex experimental conditions. Among these, FLAC3D has emerged as a leading platform, offering built-in constitutive models and powerful secondary development interfaces that enable model customization [22; 23]. For example, [PERSON] et al. [15] developed an improved Nishihara model for carbonaceous phyllite and implemented it in FLAC3D, verifying its accuracy and reliability. [PERSON] et al. [24] used energy conservation principles to derive finite difference formulations for rock elastic and dissipative energy, establishing an energy-based model to evaluate surrounding rock failure. [PERSON] et al. [25] proposed a Unified Hardening-Softening (UHS) elastoplastic model integrated with the nonlinear Hoek-Brown criterion and residual strength concepts, which was implemented via FLAC3D to simulate the nonlinear mechanical behavior of deep rock masses. Additionally, advances in the Discrete Element Method (DEM) have enhanced creep simulation capabilities. For instance, [PERSON] et al. [26] combined Rate Process Theory (RPT) with the DEM to simulate the full creep deformation process of rock masses.