# Study on the Ground Pressure Manifestation Patterns of Roof Cutting and Pressure Relief
## 3 Simulation Study on Roof-Cutting Effectiveness  
In this study, based on the roof-floor rock mass structural characteristics of Panel 81308 and the pillarless roof-cutting gob-side entry retaining (GER) design, we established a numerical model (200 m \(\times\) 10 m \(\times\) 30 m) using FLAC3D5.0 simulation software. Given the average burial depth of 440 m for coal seam #8 in Panel 81308 of Mine No. 2, and assuming an average overburden density of 2500 kg/m\({}^{3}\), the calculated vertical stress is approximately 11 MPa. Thus, an 11 MPa vertical stress (downward) and a 5 MPa horizontal stress were applied to the model's upper boundary to simulate in situ strata stress conditions. The model consists of seven vertically stratified layers. The constructed model is shown in Figure 6.  
For the simulation, we employed the Mohr-Coulomb failure criterion for rock mass assignment and the Mohr-Coulomb slip model for joint characterization; this combination accurately reflects geomechanical failure mechanisms, enabling reliable simulation of rock mass failure and joint slip behavior. Physico-mechanical parameters of coal-rock masses were determined through uniaxial compression tests, Brazilian splitting tests, and subsequent calibration, with the finalized mechanical parameters presented in Table 2.  
The simulation results, depicted in Figure 7, show that, without roof-cutting measures, the peak residual stress in the solid coal rib reached 19.8 MPa, with a cumulative vertical displacement of 26.5 mm. After implementing roof-cutting pressure relief, the peak residual stress reduced to 14.5 MPa, with the corresponding roof subsidence decreasing to 18.6 mm, demonstrating 26.8% stress concentration reduction and 29.8% deformation control improvement. The simulation verifies that roof cutting achieves the mechanical effects of stress redistribution and energy dissipation through reconstructing roof stress transmission paths. The fundamental mechanisms for reducing stress concentration and roof subsidence through deep-hole blasting roof cutting include the following:  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Stratum Name** & **Thickness (m)** & **Density (kg/m\({}^{3}\))** & **Tensile Strength (MPa)** & **Friction Angle (\({}^{\circ}\))** & **Cohesion (MPa)** & **Elastic Modulus (GPa)** & **Poisson’s Ratio** \\ \hline Overburden & 6.00 & 2500 & 4.90 & 45.50 & 3.80 & 8.50 & 0.20 \\ Strata & 5.50 & 2630 & 7.37 & 42.92 & 3.11 & 14.94 & 0.21 \\ Fang-grained & 5.50 & 2590 & 4.74 & 40.03 & 2.94 & 12.12 & 0.23 \\ Sandstone & 3.47 & 2570 & 2.71 & 39.35 & 2.32 & 2.45 & 0.26 \\ Coal seam \#8 & 3.50 & 1450 & 2.07 & 36.87 & 1.74 & 2.22 & 0.25 \\ Fine-grained & 3.19 & 2630 & 8.34 & 41.34 & 3.51 & 14.64 & 0.22 \\ Sandstone & 3.97 & 2590 & 4.56 & 39.95 & 2.84 & 11.29 & 0.24 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Rock mass mechanical parameters for numerical calculation.  
Figure 6: Numerical simulation base model.  
Figure 7: Comparison of roof-cutting vs. conventional conditions in the headgate of Panel 81308.  
1. Severing mechanical continuity between goaf and roadway roof beams, thereby reducing pressure on GER support structures;
2. Promoting timely goaf caving and effective waste rock filling, transferring overburden loads to collapsed strata to relieve GER support pressure;
3. Minimizing roof beam rotation angles (typically <15\({}^{\circ}\)) after cutting in the headgate of Panel 81308, thus reducing the predefined deformation of GER roof beams;
4. Creating artificial weak zones to control roof fracture locations.