# Stability and Control of Surrounding Rock of a Trapezoidal Roadway Retained with Hard Roof Cutting
## 4 Surrounding Rock Control Technology for Trapezoidal Top-Cutting Roadway  
### Technical Solution  
Based on key construction techniques such as pre-splitting of the top-cutting in the advanced construction of the sliced roadway, reinforcement support for the roof, coal protection on the side of the roadway, and delayed temporary support, the construction process of the sliced roadway can be divided into four stages:  
(1) Pre-split slit blasting technology was used to create artificial fracture surfaces in advance between the roadway and the roof to cut off the rock formation connection between them. Due to the control effect of the energy gathering tube, the roof rock layer in the non-top cutting direction can be well preserved; the roof rock layer in the gob will collapse along the cutting joint surface, accelerating the load-bearing of the gob waste after the panel was pushed forward.  
(2) Highly prestressed long anchor cables were used to support and reinforce the roof on the top side of the roadway. Anchor cables were used to optimize the stress state of the roof, thereby significantly improving its strength. They also can improve the integrity of the supporting structure and the supported rock stratum, so that the support load can be stably and continuously applied to the roof. The reinforced support should follow the roof pre-crack and slit process, and should be at least 30 m ahead of the working surface.  
(3) The gangue protection in the roadway prevented the gangue from the gob from flowing into the roadway and reduced its deformation. In order to limit the swollen rock blocks in the gob during the collapse of the roof and compaction of the gangue, the gangue protection in the roadway used a \"wire mesh + windshield cloth + steel fence + retractable U-shaped steel + channel steel tie rod\" support.  
(4) Temporary support was provided to support the roof, reduce the subsidence of the roof, and ensure the retention of the roadway. The temporary reinforced support in the roadways provided support for the rock strata above the support height of the anchor cables, controlling the detachment of the upper rock layer. It also limited the deflection and sinking of the basic roof, exerted a support reaction force on the roof, and promoted its movement to stabilize as soon as possible. \(\pi\)-shaped beams or industrial steel beams and single hydraulic pillars were used to form the roof support of the shed.  
The key technical parameters of the surrounding rock control for a trapezoidal top-cutting roadway with hard roof are shown in Table 2, and the key technology diagram is shown in Figure 11.  
\begin{table}
\begin{tabular}{c c c} \hline
**Material Name** & **Material Specifications** & **Remark** \\ \hline \multirow{2}{*}{Resin anchoring agent} & Z2335 & 2 top anchor cables per hole \\  & M2335 & 3 top anchor cables per hole \\ \hline Anchor cable & \(\Phi\) 21.6 \(\times\) 12,300 mm steel strand anchor cable & row spacing. 1000 \(\times\) 1000 mm \\ \hline Metal mesh & \(900\times 2400\) mm reinforced mesh. & / \\ \hline Retractable U-shaped steel & 1800 mm long 36U steel & / \\ \hline Wind screen & 3200 mm wide mine dryer cloth & Overlapping joints are used to prevent air \\  & & leakage in the roadway sections \\ \hline Barbed wire and steel fence & \(\Phi\) 8 mm cold drawn wire & The overlap length is not less than 100 mm \\ \hline \end{tabular}
\end{table}
Table 2: Key technical parameters of surrounding rock control for trapezoidal top-cutting roadway.