# Deep Soft Rock Tunnel Perimeter Rock Control Technology and Research
## 2 Roadway Surrounding Rock Control Technology
### Mechanics of Roadway Destabilization  
Stratum pressure is the inevitable result of the stress redistribution after roadway excavation and the interaction with surrounding rock deformation, which is also the essence of the mechanism leading to roadway instability. If the stress exceeds the plastic limit or strength limit of the surrounding rock, the surrounding rock will be deformed and broken. Loosening pressure, deformation pressure, and expansion pressure work together, and if the support structure is not timely or provides an insufficient support force, deformation pressure and expansion pressure will damage the surrounding rock, and then be transformed into loosening pressure, leading to the destruction of the entire surrounding rock structure due to instability. Loosening pressure tends to appear in the roof and the two gangs of the roadway, and part of the surrounding rock after stress redistribution forms a loose body, which produces the effect of bubbling down and extrusion under the influence of stratigraphic conditions and the rock structure. In addition to the loosening pressure, the role of deformation pressure cannot be ignored. Under the action of secondary stress, stress redistribution produces stress concentration. Local elastic-plastic deformation of the surrounding rock will occur, and its deformation effect on the supporting structure produces pressure. If the rock body itself has high strength, the deformation range can be controlled within the allowable range, and then in the plastic zone boundary to form a strong supporting force holding ring structure. If the body comprises weak surrounding rock with low strength, the plastic deformation is difficult to effectively control, the surrounding rock ruptures, and the deformation pressure continues to increase, leading to the destabilization of the roadway. The resistance produced by the support structure basically comes from the deformation pressure of the surrounding rock. The earlier the support structure is applied, the smaller the plastic deformation of the surrounding rock is, and the greater the deformation pressure it can endure. On the contrary, the later the supporting structure is applied, the larger the plastic deformation of surrounding rock is, and the smaller the deformation pressure is. In conclusion, the timing of the support structure is very critical: too early and it will be subjected to excessive deformation pressure, leading to the destruction of the support structure; too late and there will be too large a deformation of the surrounding rock, which may lead to the destabilization of the surrounding rock and the formation of loosening pressure [24; 25; 26]. As far as coal mine roadway engineering is concerned, the surrounding rock of the roadway is usually a layered structure, mostly made up of soft rock. As such, its overall strength is low, constrained by the roadway layout, and often affected by the mining pressure. The rupture and delamination of the rock layer are the main causes of the damage to the roof of the roadway, and the elastic-plastic deformation of the surrounding rock is completed within a short period of time after the excavation. In order to prevent further deformation of the surrounding rock, it is necessary to have a suitable support timing and support program. The relationship curve between the peripheral rock deformation \(U\) and the support resistance \(P\) after tunneling is shown in Figure 1[27]. In the relationship curve, it can be seen that if you want to minimize the peripheral rock deformation \(U\), a larger support resistance \(P\) is required, resulting in higher requirements for the support structure. When the peripheral rock deformation \(U\) exceeds the maximum permissible value, the original peripheral rock structure will be damaged, resulting in the formation of a peripheral rock loose body and the formation of loose pressure on the supporting structure, increasing the load borne by the supporting structure.