# Research on the Laws of Overlying Rock Fracture and Energy Release under Different Mining Speeds
## 2 Influence of Working Face Advancing Speed on Energy Release of Overlying Strata
### Physically Similar Simulations and Scenarios  
The core of physically similar material simulation lies in utilizing materials that mimic the mechanical properties of the prototype to create a model in accordance with the geometric similarity constant. The process involves excavating the coal body in the physical model, reflective of the actual mining conditions, and observing the collapse of the surrounding rock of the coal body and the deformation of the overlying rock. Based on the geological data of the working face and the dimensions of the model experimental frame, the model dimensions are specified as width \(\times\) height \(\times\) thickness = 2.5 \(\times\) 1.3 \(\times\) 0.2 m. The model's boundary conditions include horizontal displacement constraints at the left and right boundaries, displacement constraints at the lower boundary, and a simulated ground stress field introduced by heavy loading at the upper boundary. The simulated rock mass dimensions are 500 \(\times\) 260 m (width \(\times\) height), while the model's dimensions are 2.5 \(\times\) 1.3 m. From the simulation experiment, the geometric similarity ratio is determined to be C\({}_{\text{l}}\) = 200, the model density similarity ratio is C\(\rho\) = 1.5, and the stress similarity ratio is C\(\sigma\) = C\({}_{\text{l}}\) \(\times\) C\(\rho\) = 200 \(\times\) 1.5 = 300. The upper boundary of the rock layer is situated 72.13 m below the surface, and the two excavated working faces are located in the coal. Each working face is 1.0 m in length, with 10 cm coal pillars in the center and 20 cm boundary coal seams on both sides. The physical model rock stratum setting and similar material matching of the working face are shown in Table 1. Given that the original rock stress of this layer is 1.265 MPa, the vertical stress at the model's upper boundary is 4.22 kPa. Figure 3 shows the laying process of the overall physical similarity model. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Level**} & \multirow{2}{*}{**Rock**} & **Thickness of** & \multirow{2}{*}{**Model/mm**} & \multicolumn{2}{c}{**Ratio Number**} & **Water** \\  & & **Stratum/m** & & **(Sand/Calcium** & **Distribution** \\  & & & & **Carbonate/Gypsum)** & **Ratio** \\ \hline
17 & Water distribution ratio & 5 & 26 & 7:6:4 & 1/9 \\
16 & Mudstone & 24 & 119 & 7:8:2 & 1/9 \\
15 & Medium sandstone & 29 & 145 & 6:7:3 & 1/7 \\
14 & Mudstone & 39 & 196 & 7:8:2 & 1/9 \\
13 & Water distribution ratio & 34 & 172 & 7:6:4 & 1/9 \\
12 & Mudstone & 14 & 72 & 7:8:2 & 1/9 \\
11 & Medium sandstone & 31 & 155 & 6:7:3 & 1/7 \\
10 & Water distribution ratio & 3 & 15 & 7:6:4 & 1/9 \\
9 & Mudstone & 3 & 13 & 7:8:2 & 1/9 \\
8 & Medium sandstone & 10 & 48 & 6:7:3 & 1/7 \\
7 & Silstone & 18 & 90 & 8:3:7 & 1/7 \\
6 & Water distribution ratio & 8 & 40 & 7:6:4 & 1/9 \\
5 & Mudstone & 2 & 10 & 7:8:2 & 1/9 \\
4 & Medium sandstone & 4 & 20 & 6:7:3 & 1/7 \\
3 & Water distribution ratio & 8 & 41 & 7:6:4 & 1/9 \\
2 & Coal & 6 & 31 & 8:3:7 & 1/9 \\
1 & Water distribution ratio & 17 & 72 & 7:6:4 & 1/9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The table shows the working face physical model rock layer setting and similar material ratio scheme. Figure 3: The figure shows the laying process for the physical similarity models. In order to simulate the energy release of overlying strata under different mining speeds, verify the energy release law of the mining field under numerical simulation, and control the same amount of single excavation of the two working faces, the single excavation is 10 cm, and the time of each excavation and waiting is 30 min and 90 min. Observe the collapse deformation of the upper rock stratum. According to the buried depth of the coal seam and the properties of the rock strata, the overlying strata above the coal seam are divided into low overlying strata, middle overlying strata, and high overlying strata.