## 1 Introduction  
Due to the depletion of easily accessible coal seam resources in China, coal mining operations are increasingly delving into deeper layers, resulting in a more complex mining environment. Consequently, mining becomes more challenging, particularly in terms of roadway support [1; 2; 3]. Soft coal roadways, characterized by their low strength, soft lithology, and rheological properties, face issues such as supporting structure failures and continuous roadway deformation [4]. Given the phenomenon of creep instability in soft coal roadways, it becomes imperative to comprehend the mechanisms underlying roadway instability and propose appropriate support measures in response to roadway deformations. Therefore, a comprehensive study of the creep characteristics of soft coal, the development of a rational creep constitutive equation and creep model specific to soft coal, and an analysis of the instability mechanism of soft coal roadways form essential foundations for control technologies. The creep of soft coal and soft rock has space-time characteristics. Based on the traditional constitutive model, the time-dependent non-Newtonian fluid viscous damping element can be used to study the nonlinear creep characteristics of rock [5; 6; 7; 8; 9; 10; 11]. By conducting uniaxial and triaxial soft rock creep experiments [12; 13; 14; 15; 16; 17; 18], researchers have analyzed the influence of confining pressure on the meso-structure change of soft rock during creep. They have also proposed a nonlinear viscoelastic model to describe the deformation characteristics of the accelerated creep stage. Relevant scholars have introduced the concept of damage to accurately describe the creep behavior of soft rock and have determined the relationship between creep instability and damage variables [19; 20; 21; 22; 23; 24; 25; 26]. Due to the lack of coupling between the support structure and the surrounding rock in terms of strength, stiffness, and deformation, some scholars [27; 28; 29; 30] suggest that the key sections of the roadway's surrounding rock should be reinforced using bolt-mesh-cable coupling support technology. Alternatively, they propose establishing a model that considers the anchoring force of bolts and the deformation of the rock mass to accurately describe the creep failure of the roadway. Through an analysis of the internal crack development within the rock mass, as well as the internal composition of soft rock and the primary load transfer paths within the surrounding rock, relevant scholars [31; 32; 33; 34] have uncovered the deformation mechanisms responsible for the internal collapse of the two sides of the roadway, roof collapse, and floor heave. Aiming to address the creep instability of deep soft rock roadways and asymmetric deformation roadways, the researchers analyze the instability mechanism. They propose a roadway reinforcement technology based on the principles of hierarchical and staged support, structural compensation of key components, and secondary support to enhance the stability of the surrounding rock [35; 36; 37; 38; 39]. Although extensive research has been conducted on the support of soft coal roadways by scholars, the analysis of creep characteristics in soft coal rock often treats it as a continuous body. However, considering the low strength and granular, discrete nature of soft coal rock, a more realistic approach would be to utilize the discrete element method for simulating the creep mechanical behavior of coal rock. Based on the aforementioned analysis, this paper focuses on the return air roadway of the 11,000 working faces in Quandian Coal Mine as the specific engineering background. The study utilizes laboratory tests, theoretical analysis, numerical simulation, and industrial testing to unveil the mechanism of creep instability in soft coal roadways. Furthermore, the research aims to determine an appropriate roadway support scheme and conduct industrial testing.