# Stability Control of Multilayer Roof Strata in the Large Mining Height Gob-Side Entry: A Case Study
## 1 Introduction  
Gob-side entry is widely adopted in coal mines across China due to its various advantages, including increased recovery rates, reduced tunneling times, lower roadway maintenance costs, mitigation of corner methane accumulation and enhanced mining economic benefits [1, 2, 3, 4]. In general, gob-side entry retaining technology can significantly boost coal recovery rates [5, 6, 7, 8], making it an effective method in thin coal seam mining conditions [8, 9]. To investigate coal pillar stability and gob-side entry deformation characteristics at varying distances from the advancing working face, [PERSON], et al. [10] conducted finite element simulations by incorporating a double-yield model for gob materials, and cooperative control strategies of surrounding rock stability were proposed to deal with coal pillar deformation. Similarly, [PERSON], et al. [11] examined the stability of gob-side entries across various coalfields and analyzed the factors influencing roadway deformation, including mining depth, support strength and the area of the gob-side hanging roof. A series of key technologies for controlling surrounding strata in the gob-side entry were introduced, including methods for presplitting pressure relief, district control, structural parameters optimization and rapid construction of the roadside wall [12, 13, 14, 15]. Despite these advancements, the application of the gob-side entry retaining technique to mines with compound roof strata is still a challenge. Compound roofs, which are widely distributed in coal mines, consist of interlayers of soft and hard rock strata [16; 17; 18]. After mineral extraction, the lower roof tends to exhibit greater deflection than the upper rock strata, while the cohesion between these layers is often low, leading to roof separation. Generally, compound roofs have the characteristics of low compressive strength, loose transibility, weak self-stability, poor integrity and a disparity in mechanical properties between different rock strata [19; 20]. [PERSON], et al. [21] established a mechanical model for describing the deflection of a compound roof based on the beam theory for elastic foundation. Their mechanical analysis revealed key factors associated with roof caving and rib spalling during mining activities in large mining height entries with compound roofs. In order to better understand the deformation and failure mode of large cross-sectional long-wall mining roadways under compound roofs, [PERSON], et al. [22] developed a theoretical model assessing the effects of caving methods and supporting strength on the stability of surrounding strata. In a case study analyzing roadway stability under compound roof conditions, [PERSON], et al. [23] identified quality control as a critical concern for surrounding rock stability. To explore the effective reinforcing roof bolting strategies in compound roof conditions, [PERSON], et al. [24] investigated the effects of layered roof strata on surrounding rock stability. By taking Qujiang Coal Mine as an example, [PERSON], et al. [25] performed a field investigation, theoretical analysis and an industrial test to determine the comprehensive control technologies, e.g., the main body was supported by prestressed truss and anchor rope, and the accessory body was reinforced by cable-anchor-mesh. Their engineering application showed that roadway deformation was markedly controlled by means of the comprehensive control technology. Focusing on compound roof conditions in Xinji area, [PERSON], et al. [26] elucidated the chain reaction mechanisms triggered by widespread rib spalling and collapse in mining panels with large, inclined angles. They also proposed a grouting filling method with high-water filling materials to ensure safe and efficient mining activities in compound roof working faces. Additionally, based on experimental results and energy balance theory, [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [19] proposed two support principles for testing roadways.