# Improving Hard Rock Materials Cuttability by Hydraulic Fracturing at Mining Working Face
## 1 Introduction
### Comparison and Analysis  
The effects of the three testing schemes are compared as follows. When the advancing distance of the working face reaches the fracturing depth of scheme A, the implementation  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Evaluation**} & \multicolumn{3}{c}{**Nos. 80–86 Hydraulic Supports**} & \multicolumn{3}{c}{**Nos. 87–93 Hydraulic Supports**} & \multicolumn{3}{c}{**Nos. 94–100 Hydraulic Supports**} & \multicolumn{3}{c}{**Decrese Rate (\%)**} \\ \cline{2-13}  & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** & **Scheme** \\  & **A** & **B** & **C** & **A** & **B** & **C** & **A** & **B** & **C** & **A** & **B** & **C** & **A** & **B** & **C** \\ \hline Average current ratio (\%) & 79.43 & 98.96 & 101.71 & 47.10 & 44.00 & 42.40 & 76.60 & 72.30 & 74.16 & 39.63 & 48.59 & 51.70 \\ Consumption number of picks (piece) & 10 & 9 & 10 & 5 & 4 & 3 & 9 & 9 & 8 & 47.30 & 55.50 & 70.00 \\ Shearer cutting time (min) & 252 & 238 & 229 & 80 & 56 & 37 & 241 & 249 & 245 & 77.53 & 85.16 & 89.93 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Effect evaluation of schemes.  
Figure 17: Mining working face: (**a**) the shearer cut down the rock blocks at the fracturing section; (**b**) hydraulic fractures formed in the hard rock fault after hydraulic fracturing.  
process of scheme B will be carried out; when the advancing distance of the working face reaches the fracturing depth of scheme B, the implementation process of scheme C will be conducted. Compared with schemes A and B, the average current ratio in scheme C decreases by 12.07% and 3.11%, respectively; the consumption number of picks decreases by 2 and 1, respectively; and the time of the shearer cutting through the target section shortens by 53.75% and 33.93%, respectively.  
Although scheme C increases the borehole number, it only takes 52 min to completely fracture the nine boreholes due to the simultaneous fracturing process of two boreholes. The fracturing duration is the same as that in schemes A and B. Furthermore, scheme C has more prominences in the average current ratio, the loss of picks and the shearer cutting time. The dip angles of the boreholes in scheme B are all 45\({}^{\circ}\), shortening the projected distance of the borehole in the advancing direction of the working face. When the dip angles of the lower row boreholes in scheme C are 0\({}^{\circ}\), the fracturing processing area is much wider. Subsequently, scheme C was selected to implement hydraulic fracturing in the hard rock fault with a dip length of 70 m along the working face. No hydraulic fracturing was carried out from September 5 to 10, and a hydraulic fracturing field test was carried out on September 11. The daily advance distance of the coal working face from September 12 to 18 was 2.4 m. An average of nine picks were consumed per day. After fracturing the hard rock fault, the shearer passes through the hard rock fault smoothly, the equipment loss is reduced, and at the same time, the advance distance of the working face can reach 2.4 m per day.  
Compared with the untreated section, the current ratio of the shearer passing through the target section is reduced by more than 39.63% and the cutting efficiency is increased by more than 77.53%, indicating that hydraulic fracturing can practically improve the cut-tability of the rock mass and facilitate the mechanized rock fragmentation. Consequently, scheme C is selected as the final hydraulic fracturing scheme. Compared with schemes A and B, scheme C presents a significant decrease in the average current ratio, the consumption number of picks and the time of the shearer cutting through the fracturing area. The borehole dip angle is 45\({}^{\circ}\) in the upper row and 0\({}^{\circ}\) in the lower row in scheme C, which helps to produce complex radial and axial fractures in the rock mass. The pretreated rock mass can be hydraulically fractured in layers.