# Instability Characteristics of and Control Techniques for Mudstone-Clay Composite Roof Roadways
## 1 Introduction  
Coal seam roof lithology exhibits non-singular characteristics due to variations in surface sedimentary environments during its formation [1]. These formations typically comprise heterogeneous soft and hard interlayered rock layers, frequently containing weak interlayers such as thin coal seams [2, 3]. These weak interlayers are characterized by a loose structure, poor mechanical properties, and an uneven distribution. During loading and unloading processes, they create local stress concentrations, leading to significant roadway-surrounding rock (RSR) and increasing the risk of roof collapse [4, 5, 6, 7]. Through an investigation of the deformation results of numerous composite mudstone roof roadways, it was found that the influence of the rock water and surface water supply is significant, coupled with the impact of water injection when drilling during construction, causing the mudstone and clay layers to remain in a water-bearing state for a long time [8, 9]. The characteristics of rocks are susceptible to influences from other natural factors. Temperature changes can influence the mechanical properties and deformation behavior of rocks, particularly those with clay minerals, due to thermal expansion and contraction effects [10]. Long-term weathering processes, such as repeated wetting and drying cycles, can lead to the degradation of rock strength and the development of microcracks [11]. Mining-induced vibrations from blasting and mechanical excavation can also contribute to the destabilization and failure of the surrounding rock mass [12]. Natural influencing factors and the vibration waves cause the particles between rock blocks to loosen. The flow of surface water becomes more significant, resulting in an increase in the moisture content of the roof rock strata. In this context, the coupling between the composite roof and groundwater in a rock mass significantly influences the deformation and failure of the surrounding rock following roadway excavations [13]. When exposed to water, the composite roof, with the mudstone containing clay minerals, exhibits strong swelling [14]. After encountering the water, the bonding between the particles within the mudstone is disrupted, leading to disintegration and softening [15; 16]. Notably, the water-induced softening and disintegration of mudstone represent macroscopic characteristics that manifest through microstructural changes [17]. Furthermore, clay rocks, characterized by their hydrophilicity and small particle size, undergo distinct changes when water penetrates their pores and cracks: the adsorbed water film of small rock particles thickens, while cement components soften or dissolve. These mechanisms ultimately lead to particle collapse, disintegration, and volume expansion [18]. The evolution process of delamination in large cross-section coal roadway composite roofs progresses through distinct stages: roof deflection, interlayer shear deformation, non-coordinated deformation, and delamination expansion [19]. Multiple factors influence coal roadway deformation and failure including the surrounding rock structure, geostress, groundwater, and support parameters. Notably, the roof layer thickness directly affects both the surrounding rock deformation and failure mode, while contributing positively to the main roof stability [20]. Within this system, the roadway width, lateral pressure coefficient, and layer thickness significantly influence the delamination deformation in the composite roof [21]. In composite rock layers, the radial stress in the softer rock mass is lower than in the harder rock mass, indicating that weak rock layers cause variations in the surrounding rock's mechanical behavior [22]. High stress levels lead to shear failure and delamination in weak interlayers and lower rock masses. The failure mode of roof detachment with weak interlayers is determined by the stress state, thickness, number, spatial position, and failure condition of the weak interlayers [23].