# Study on the Stability and Control of Gob-Side Entry Retaining in Paste Backfill Working Face
## 1 Introduction  
For a long time, coal has played a pivotal role as a fundamental energy source in China, holding a critical position in the energy supply [1, 2, 3, 4]. It serves as a key pillar for ensuring national energy security and has significantly contributed to China's economic construction and social development [5, 6, 7, 8, 9]. However, with the adjustment of the energy structure and the increasing emphasis on environmental protection, it has become essential to strengthen the research and development of green mining technologies [10, 11]. Effortsmust focus on improving the utilization efficiency of solid waste, such as coal gangue and fly ash, and minimizing the environmental impact of coal production [12; 13; 14; 15]. As a pillarless mining method, the GER technique plays a critical role in reducing roadway excavation rates, alleviating mining-extraction scheduling pressures, and improving coal recovery rates. However, traditional GER techniques typically manage the overlying strata of the gob using a caving method, as illustrated in Figure 1a. As the mining face advances, the overlying strata fracture and collapse, leading to severe mine pressure manifestation. This results in surface subsidence, building collapses, and disruption of surface hydrology make it challenging to control roadway stability [16; 17; 18; 19]. Additionally, the accumulation of coal gangue at the surface leads to land occupation and environmental pollution, potentially causing a series of social and environmental issues [20; 21; 22; 23]. In contrast, the GER with paste backfill technology retains the advantages of traditional GER while employing a filling method to manage the overlying strata. As shown in Figure 1b, the backfill material is introduced into the gob in a timely manner as the coal seam is mined [24]. Once compacted and fully bonded to the roof, the backfill material provides certain strength and load-bearing capacity, which limits the roof fracturing and caving. This prevents significant cyclic pressure-induced phenomena in the mining face, effectively reducing mine pressure manifestations and surface subsidence, thus significantly enhancing roadway stability [25; 26; 27; 28]. Furthermore, materials such as coal gangue and fly ash can be processed into slurry filling materials, promoting the resource utilization of solid waste and contributing to the coordinated development of coal mining and ecological environmental protection [29; 30; 31; 32]. Many scholars have conducted in-depth research on filling mining technology. [PERSON] [33], through physical model experiments, demonstrated that fly ash mixtures can be used as backfill materials in gob, effectively mitigating the impact of underground mining on the surface. [PERSON] et al. [34] backfilled coal gangue and fly ash in a 1:0.35 ratio into gob, achieving a surface subsidence of only about 170 mm after mining, which effectively controlled surface settlement and protected adjacent buildings and structures. [PERSON] et al. [35] used UDEC 6.0 software to simulate the impact of different backfill ratios of ultra-high-water backfill material on the movement of overlying strata. By comparing the vertical displacement and vertical stress distributions, they identified optimal filling and water content ratios of 90% and 95%, respectively. [PERSON] et al. [36] outlined the basic principle of surface subsidence control: ensuring maximum safety standards for surface buildings by controlling the backfill body compression ratio. While these studies primarily focus on the effectiveness of the filling method in controlling surface subsidence, limited  
Figure 1: Differences in environmental damage between the caving method and the filling method: (**a**) caving method; (**b**) filling method. research addresses the stability mechanisms and control technologies of GER in filling working faces. Therefore, this study takes the CT301 filling working face of Chahasu Coal Mine as engineering background and the CT301 headgate as research object.