# Stability and Control of Surrounding Rock of a Trapezoidal Roadway Retained with Hard Roof Cutting
## 3 Deformation and Control Mechanism of Surrounding Rock for a Top-Cutting Roadway
### Control Mechanism of Surrounding Rock  
When performing top-cutting and roadway retention in an irregular trapezoidal roadway, the particularity of the surrounding rock control was mainly reflected in the uneven stress distribution, unbalanced cantilever beam effect of the roof, significant differences in surrounding rock deformation and complex stress transfer. The special structure of a trapezoidal roadway can lead to asymmetric stress distribution in the surrounding rock, especially with significant stress distribution differences in the roof and side, which were prone to forming stress concentration areas and thus affecting the stability of the surrounding rock. In this situation, top-cutting can disrupt the continuity of the hard roof to change the stress transfer path of the roof (Figure 10), alleviating stress concentration in the roof and side of the retained roadway, and reducing the pressure of the roof on the roadway. The specific control mechanism is as follows:  
(1) Forming cantilever beam structure after cutting the roof: by cutting the middle or the sides of the roof, the stress state of the rock strata is changed to form a \"cantilever beam\" structure. Under this structure, the load on the rock strata is partly transferred to the support structures, reducing the pressure on the roadway's roof.  
(2) Arch structure and stress transfer: The roof forms a structure that is similar to a \"self-supporting\" arch, resulting in stress redistribution. The load on the roof is borne by the support system on both sides of the roadway, thereby controlling the deformation within the roadway and enhancing its stability.  
(3) Energy release and fracture evolution: After top-cutting of the hard roof, stress within the rock strata will partially release, and fractures gradually form in the rock mass near the top-cutting area, which helps to reduce the overall pressure on the roof and to concentrate the deformation in the top-cutting area rather than in the interior of the roadway.  
According to the above analysis, the stability control of the roof after the top-cutting was the core of the stability control of the surrounding rock in the top-cutting and retained roadway, especially the control of the roof on the top-cutting side. After the top-cutting, the roof on the top-cutting side will undergo sliding shear failure along the top-cutting line. However, the roof on the top-cutting side can be suspended in the upper stable rock strata by using the combined long anchor cable support. In addition, since the height of the top-cutting side roadway was smaller than the top-cutting height, it collapsed after mining the panel to form one side of the retained roadway. According to the simulation results, it can be seen that the deformation of the surrounding rock of the retained roadway was slight. The control of the surrounding rock was mainly to prevent the gauge of the gob  
Figure 10: Stress transfer mechanism between surrounding rocks of roadway after top-cutting.  
from jumping into the roadway to cause damage to equipment or people. The retained roadway should also preserve a strong ability to prevent wind leakage. Methods such as laying waste nets, erecting waste walls and adding windshield cloth can be used to provide waste protection and wind leakage prevention.