# Instability Characteristics of and Control Techniques for Mudstone-Clay Composite Roof Roadways
## 1 Introduction
Weak interlayers frequently initiate composite roof failure along and through layers. Moreover, as the number of weak interlayers increases, the sliding deformation above them intensifies, while the compression deformation in the interlayers decreases. The failure mode transitions toward single tensile failure, increasing both the height of the roof and the risk of roof collapse [24; 25]. The management of extremely soft roadways with weak interlayers can be improved by leveraging the RSR's self-supporting capacity, based on the layered beam principle. This approach incorporates high-strength anchor rods, fully bonded high-strength anchor bolts, and prestress for effective support [26]. During the excavation, the prestressed anchor bolt stage enhances inter-block interaction forces, substantially increasing the RSR's bearing capacity compared to initial stress levels [27]. Long anchor cables effectively control displacement differences between the short anchor cable anchorage section and the surrounding rock, preventing the collapse of shallow surrounding rock. These cables accommodate significant deformation, making them suitable for the adaptive deformation of composite soft RSR. The anchorage section of the long anchor cable lies within the elastic range of the rock formation, enhancing the safety of the support system. The stress super position principle in the formation layer of anchor rods and cables--combined with the composite double-arch structure--effectively stabilizes the coal mine roadway-surrounding rock [28]. Through the anchoring structure's radial action, which compresses the various composite roof rock layers, the frictional forces between rock layers are increased, forming a composite beam that further strengthens their stability [29]. In roadways with high-moisture-content roofs, the axial stress in the anchor body increases from the initial anchoring point to the anchor rod end. To mitigate the effects of mine water on mechanical properties in shallow soft RSR, full-section high-strength drainage reinforcement joint control technology is applied. This reduces the tensile failure caused by the mine water's interaction with the soft rock, thus enhancing the support system's performance and preventing deterioration [30]. Additionally, soft rock roadways experience pronounced mining-induced roof displacement due to the material's inherent deformability. To address this challenge, a joint support system combining anchor rods and a mesh is proposed. This system controls the energy released from compression, reducing surrounding rock deformation and maintaining roadway stability during mining activities [31]. While numerous joint support and prevention technologies exist for composite roof structures, research on micro-level factors and double soft roadway deformation remains limited. In China's western mining areas, the relatively recent coal formation and shallow burial of coal seams, influenced by sedimentation and plate compression movements, have resulted in widespread weakly cemented soft strata within coal-bearing formations. To examine the deformation characteristics of mudstone-clay composite roof roadways, XRD analysis and SEM are integrated to investigate the micro-mechanisms of softening and disintegration in mudstone-clay composites; a systematic investigation of the macroscopic failure characteristics of mudstone-clay composites is carried out under different influencing factors using uniaxial loading experiments; an orthogonal experimental design is used to reveal the factors affecting the deformation sensitivity of composite rock roadway roofs; effective deformation control strategies and support technical parameters are developed based on the micro-level investigations and macroscopic failure characteristics; and the specific geological conditions of shallow-buried mudstone-clay composite roofs in Shanxi, China are investigated, which have not been extensively studied before.