## 4 Similarity Simulation Experiments
### Simulation Experiment Process  
The model was horizontally layered, with mechanical parameters for each layer calculated using a similarity ratio based on experimental workface data. Proportioning tests with aggregate (fine river sand), cementing materials (gypsum and lime), and layering material (mica powder) determined the experimental proportions. The material volumes were then determined and laid out according to layer thickness, geometric similarity, and test bench size. The constant external force is used to simulate the self-weight of overlying strata caused by the buried depth of coal seam. After air-drying and ensuring layer strength, excavation tests were performed. The final laid-out and dried model is depicted in Figure 12.  
This model is designed to investigate the deformation characteristics of roadway surrounding rock and overlying coal strata during main roof fracturing in the mining process. During coal seam extraction, the immediate roof collapses progressively with mining advancement, while stress concentration effects gradually develop in the roadway roof. When the fractured main roof blocks rotate to a critical angle, they ultimately induce  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Rock Formation**} & \multirow{2}{*}{**Actual Thickness**} & \multirow{2}{*}{**Layer Number**} & \multirow{2}{*}{**Quality Ratio of Sand,**} & \multicolumn{3}{c}{**Quantity/kg**} \\ \cline{4-7}  & & & & **Lime, and Gypsum** & & **Sand** & **Lime** & **Gypsum** & **Water** \\ \hline Overlying strata & 10 & 3 & 6:0.5:0.5 & 13.1 & 1.1 & 1.1 & 1.2 \\ Main roof & 15 & 5 & 7:0.6:0.4 & 20.0 & 1.7 & 1.1 & 1.9 \\ Immediate roof & 4 & 2 & 6:0.5:0.5 & 6.5 & 0.5 & 0.5 & 0.6 \\ Coal seam & 19 & 5 & 8:0.7:0.3 & 20.4 & 1.8 & 0.8 & 1.9 \\ Immediate bottom & 5 & 2 & 6:0.5:0.5 & 6.5 & 0.5 & 0.5 & 0.6 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Similarity model material mass ratio.  
Figure 12: Similarity simulation test model.  
shear failure in the coal seam along the fracture line. Notably, the position of the fracture line (1.5 m or 2.5 m from the coal pillar side) not only controls the propagation range of shear failure in the overlying coal seam but also determines the severity of roadway damage, demonstrating significant spatial correlation between these factors. Figures 13 and 14 clearly illustrate the localized instability occurring in the roof structure.  
The deformation characteristics of overlying coal strata during main roof fracturing, as obtained from the physical similarity simulation experiments, demonstrate remarkable consistency with the numerical simulation results. These findings conclusively demonstrate that the combined effects of coal seam extraction and MRFL development exert substantial influence on roadway stability. To address these challenges, the implementation of high-strength bolt-cable support systems becomes imperative. Specifically, this study proposes an innovative support scheme utilizing a novel five-hole large bearing plate integrated with bolt-cable systems, which has been specifically designed to counteract the destabilizing effects observed in both experimental and numerical analyses.