# Study on the Ground Pressure Manifestation Patterns of Roof Cutting and Pressure Relief
## 2 Project Overview
### Ground Pressure-Monitoring Scheme for Gob-Side Entry Retaining with Roof Cutting  
After implementing the pillarless mining technology of gob-side entry retaining with roof cutting and pressure relief, in order to facilitate the formulation of subsequent mining measures for Panel 81308, it was necessary to monitor the stress conditions and deformation of the roadway and working face. The surrounding KJ1100 coal mine rock dynamic monitoring system for gob-side entry retaining (excavation) was adopted; this system consists of a central station computer, a KZG18 intrinsically safe mine signal converter, a GMY500 intrinsically safe mine bolt (cable) stress transmitter, a GUD2000 intrinsically safe mine displacement sensor, and other equipment. The monitoring system flowchart is shown in Figure 3. The main working principle is as follows: the data collected from each sensor are transmitted to the central station computer through the signal converter, and the central computer performs information storage and analysis. The system monitors parameters such as the working resistance of powered supports and the shrinkage of powered support legs in real time; these data are used to evaluate the rationality of support parameters in the working face and roadway, as well as to study the movement laws of the roof strata.  
In this section, we detail the monitoring scheme designs for both the roadway and working face. The specific arrangements are described below.  
For the retained roadway section of the headgate of Panel 81308, starting from 68 m behind the setup room to the stopping line, one monitoring station was installed every 50 m. Each station consisted of one roof separation monitor and one constant-resistance cable bolt stress monitor. The system collected data every 30 min. The monitoring equipment is shown in Figure 4.  
Within working face 81308, one pressure-monitoring point was installed every 30 m, totaling seven pressure-monitoring points. The system collected data every 30 min. The layout schematic of the monitoring stations and points is shown in Figure 5.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Remarks and Explanations** \\ \hline \multirow{2}{*}{Borehole position} & \multirow{2}{*}{200–500 mm} & Distance from mining rib to cutting seam holes in the headgate of Panel 81308: 200–500 mm \\  & & 15\({}^{\circ}\) \\ \multirow{2}{*}{Cutting seam dip angle} & \multirow{2}{*}{13 m} & \multirow{2}{*}{Inclined length of cutting seam holes} \\ \multirow{2}{*}{Borehole inclined length} & \multirow{2}{*}{50 mm} & \multirow{2}{*}{—} \\  & & \\ \multirow{2}{*}{Borehole diameter} & \multirow{2}{*}{50 mm} & \multirow{2}{*}{—} \\ \multirow{2}{*}{Energy-gathering tube} & \multirow{2}{*}{BTC35-1 500} & Outer diameter: 42 mm; inner diameter: 36.5 mm; charge diameter: \(\Phi\)35 mm; single section: 1.5 m \\ \multirow{2}{*}{Emulsion explosive} & \multirow{2}{*}{Grade III} & Specification: \(\Phi\)35 \(\times\) 200 mm; single cartridge \\ \multirow{2}{*}{Borehole spacing} & \multirow{2}{*}{500 mm} & \multirow{2}{*}{Department based on field test results} \\ \multirow{2}{*}{Charge structure} & \multirow{2}{*}{\(5+4+4+3+2+1\)} & Single hole uses six energy-gathering tubes; stemming length: 4.0 m; 19 cartridges per hole \\ \multirow{2}{*}{Maximum simultaneous detonation holes} & \multirow{2}{*}{15 pieces} & Post-blast gas concentration \(<\) 0.5\%; CO \\  & & concentration \(<\) 0.0024\% (24 ppm) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Design parameters of advanced roof pre-splitting drilling and blasting.  
Figure 4: Monitoring equipment diagram.  
Figure 5: Layout of ground pressure monitoring stations in Panel 81308.  
Figure 3: Monitoring system flowchart.