## 1 Introduction  
Due to old age and lack of maintenance, the roadway's surrounding rock deformation and damage are serious. During the mining period--especially in the vertical distribution with the working face towards the abandoned roadway--the surrounding rock of the abandoned roadway has difficulty withstanding the influence of the working face over the front support pressure and the phenomenon of roof fracture, which are two types of instability. The working face passes through the abandoned roadway with a large span and for a long time, which is detrimental to its safety and stability [1; 2; 3; 4; 5; 6]. At present, domestic and foreign control of the rock surrounding the abandoned roadway mainly involves the use of pillars and wood pallets to support the roof of the abandoned roadway. However, the support strength of the pillars and wood pallets is low and cannot effectively prevent the roof of the abandoned roadway from sinking. By contrast, anchor rods have good support performance, but the cost of support is higher, and they are not conducive to the normal cutting of the face back to the miners. Somemines set up the working face to bypass the abandoned roadway, use the abandoned roadway as a cutting hole, or use the working face as a cutting hole; however, this makes the working face unsafe and unstable. Therefore, some mines arrange the working face so that it bypasses the abandoned roadway, but this is often restricted by the engineering and geological conditions, coupled with the complexity of relocating the working face. Since it is affected by the existing roadway, the working face cannot be rearranged to bypass the abandoned roadway. It has been proven in practice that grouting and filling abandoned roadways using filling materials to reinforce the two sides of the road and the top of the broken surrounding rock body can ensure the safety and stability of the working face when crossing the abandoned roadway. At present, mining scholars at home and abroad have been committed to conducting research on filling materials and filling technology for abandoned roadways and have achieved success in mining practice. Research and development of inorganic cementing filling materials are especially gaining increased attention [7; 8; 9; 10; 11; 12]. Using abandoned roadway filling technology is an effective way to suppress the deformation and damage of the roadway peripheral rock when the working face passes through the abandoned roadway, which is of great significance for the smooth passage of the coal mining face through the abandoned roadway, the realization of safe and efficient mining of the mine, and the improvement of the extraction rate of coal resources. However, the research and development of filling materials are major problems when filling abandoned roadways. At present, more representative filling materials mainly include high-water quick-setting materials, Remy filling materials, and inorganic cementitious materials that are mainly based on foamed cement [13; 14]. High-water quick-setting materials, such as abandoned roadway filling materials, as a whole, have poor cementing performance and bonding roller, are not easy to wash, and are expensive. With Remy filling materials, due to their britteness, cutting can easily cause strong vibrations in the coal mining machine, which is not conducive to the safety and stability of the working face [15; 16; 17; 18]. Based on the above problems, this paper conducts experimental research on the inorganic cementitious materials that are mainly based on foamed cement, from the independent research and development of materials to the improvement of the filling process and equipment adaptation, forming a complete set of filling systems. The research results have been applied onsite to the filling of the abandoned roadway of the 3122 comprehensive discharge face in the Jingxin Coal Industry; significant results have been achieved.