## 3 Feasibility Determination of GSCRF and Surrounding Rock Control Theory
### Roadway Stress Environment and Surrounding Rock Damage  
In the process of GSCRF, the mining roadway is formed in a unique way from traditional pillar-based roadway protection and gob-side roadway forming technique. The stress environment is also different. Ensuring roadway surrounding rock control during the mining of the first and next working faces is the key to pillarless mining by the GSCRF process.  
Under GSCRF, the stress environment of the mining roadway has the following characteristics:  
1. The roadway is in the low stress area; the solid coal side has been crushed and damaged and lies in the internal stress field where the stress is low; at the gob side where the gangue is not anchored by bolts and cables, the stress is modest, too.
2. The immediate roof of the coal seam being mined is broken, has low strength and accommodates many cracks. Therefore, there may be considerable strata behavior in the roadway space.
3. The gangue in the gob can easily slip into the roadway to affect the internal space of the roadway.
4. There is no coal pillar at the gob side; the roof is not supported and can deform badly.  
The instability of the mining roadway mainly results from the action of loosening pressure, deformation pressure and expansion pressure on the surrounding rock supporting  
Figure 9: No impact on gangue (**a**) The main roof is not impacted (**b**) The main roof is impacted.  
\begin{table}
\begin{tabular}{c c} \hline \hline The thickness of the immediate roof is large; the fallen gangue is less than 1 m from the main roof, as shown in Figure 9a. & The thickness of the immediate roof is too small; the fallen gangue is more than 1 m from the main roof, as shown in Figure 9b. \\ \hline \(\Delta H=H+H_{ir}-H_{ir}K_{a}<1m\) & \(\Delta H=H+H_{i}-H_{i}K_{a}>1m\) \\ \hline The gangue is not far from the main roof; the main roof rock beam bends and sinks to touch the gangue, which has no impact on the gangue and does not threaten the safety of the roadway. & The gangue is too far from the main roof; after the end and middle of the main roof are cracked, a large amount of bending elastic energy will be released; the gangue will also be greatly impacted, thus affecting the safety of the roadway. \\ \hline \hline \end{tabular}
\end{table}
Table 3: Determination of gangue impact [40].  
structure. If the roadway work is not supported in time, the deformation pressure and expansion pressure will damage the surrounding rock and turn into loosening pressure, causing the surrounding rock to become unstable.  
After the gob-side caving roadway is formed, under the action of secondary stress, the surrounding rock will be locally plastically, viscoelastically or visco-elastoplastically deformed. The force of the loosening rock mass will directly act on the roadway support, causing the surrounding rock stress to be redistributed. Part of the surrounding rock or its structural surface will detach from the parent rock and become a separate block and a bulk mass. Under the action of gravity, it will overcome minor resistance to produce caving and slump movements, causing the surrounding rock to become structurally unstable.