# Research and Application of Foam Filling Material in Soft Rock Roadways
## 7 Conclusions  
This paper addresses the issues of roof falls in the soft rock roadway of Songxian Shanjin Gold Mine, as well as the inefficacy of traditional support methods. It proposes a bag-filling scheme that effectively mitigates the risk of roof falls through the independent research and development of foaming materials and bag-filling techniques, accompanied by mechanical analysis, laboratory tests, and field trials. The following conclusions are drawn:  
1. In the soft rock roadway of Songxian Shanjin, due to its relatively low physical and mechanical properties, the natural fractures in the rock may collapse during the blasting and mining process. The existing timber fill support methods cannot meet the required support strength. The self-developed foam material overcomes the problems of timber fill not being able to fully contact the roof, as well as the issues of wooden structures being prone to corrosion and strength reduction, effectively preventing roof collapse accidents.
2. When the solid-water ratio of the foaming material exceeds the A3 level, the change in slurry viscosity is minimal, occurring at a ratio of 1:2. During the actual filling process, the mixed slurry requires a flow time of about 15 min, meaning the initial setting time of the material should exceed this duration, leading to a minimum water-solid ratio of 2.5:1. When seeking to incorporate more foam, maintaining a water-solid ratio between 2.5:1 and 3.0:1 results in a foam loss percentage of less than 44%. The final strength of the foaming material with water-solid ratio of 1.5:1 and 1:1 increases by approximately 47.7% compared to the strength at 1 day. Additionally, when the concentration of the foam stabilizer is at 1.0%, it reaches a peak effectiveness, indicating that this concentration is optimal. Based on practical requirements, a ratio of 1:3 for portland cement to water was selected, with a foam stabilizer concentration of 1%. This ensures sufficient flow time while meeting the strength requirements for filling support.
3. Using high-quality waterproof canvas bags and self-developed foaming materials, a new bag-filling process was proposed. The filling cost was reduced from 800 CNY/m\({}^{3}\) to 545 CNY/m\({}^{3}\), a decrease of approximately 32%. The required workforce was reduced from 4 workers to 2, cutting labor costs by 50%. It is estimated that annual support costs can be reduced by about CNY 300,000. The bag-filling scheme was used to fill and reinforce the roof falls area in the roadway. This improved the support strength of the filling material, fundamentally eliminating the conditions  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multirow{2}{*}{**Labor Cost**} & \multicolumn{3}{c}{**Economic Cost**} \\ \cline{3-5}  & & **Materials** & **Unit Price** & **Filling Cost** \\ \hline Log pack & 4 people & Pit timber & 800 CNY/m\({}^{3}\) & 800 CNY/m\({}^{3}\) \\ \hline \multirow{3}{*}{Material filling} & \multirow{2}{*}{2 people} & Foam filling material & 2000 CNY/t & 500 CNY/m\({}^{3}\) \\ \cline{3-5}  & & High-quality waterproof canvas bag & 300 CNY/per piece & 45 CNY/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of filling costs.  
for fire hazards and reducing the likelihood of secondary collapse accidents. Roof displacement was monitored continuously for three months, showing no significant subsidence. This effectively ensured the safety of the roadway roof surrounding rock.  
Writing--original draft, writing--review and editing, C.L.; project administration, funding acquisition, H.N.; supervision, W.Z. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflicts of interest.