## 4 Verification of Pressure Relief Effect of Roof Cutting and Roadway Retention  
Advanced pre-splitting blasting of the 7135 working face was implemented at the boundary of the roof plate in air return roadway, with a cutting height of 9 m, an angle design of 80\({}^{\circ}\) in the horizontal direction, a spacing of 0.6 m between blast holes, a charging length of 4 m, and a sealing depth of 2 m. Pre-splitting blasting was carried out at a height of 50-60 m in advance of the working face using a concentrated energy blasting process. The 7135 working face only tested a 334-m section without coal pillars, and the lagging working face roadway support adopted an \"anchor mesh cable + reinforced anchor cable support + temporary stack support\", as shown in Figure 7.  
Figure 7: Backward working face roadway support section.  
The roof anchor rod support of the roadway adopted threaded steel with a diameter of 20 mm \(\times\) 2.4 m and a spacing of 0.8 m \(\times\) 0.8 m. The anchor cable was made of steel strands with a diameter of 21.6 mm \(\times\) 10.3 m, and the step arrangement was 1.5 m \(\times\) 1.6 m. The stacked support adopted double-row support, and the specification parameters for the reinforcing anchor cables were as follows: steel strands with dimensions of 21.6 mm \(\times\) 12.3 m, and a single row with a spacing of 800 mm. After stabilizing the roadway, the temporary reinforcement support, namely the stack-type support, was withdrawn.  
During the period of retaining the roadway, measurements of stress on the reinforcement anchor cable and deformation of the roadway roof subsidence were taken, as shown in Figures 8 and 9.  
In Figure 8, it can be seen that during the retention period, the force on the anchor cable first increased and then stabilized. During the mining retention period, the range of 0-160 m behind the working face was identified as the impact stage of the retained roadway. During this stage, the force on the reinforced anchor cable showed an increasing trend, and the range of 160-300 m behind the working face was identified as the stable stage of the retained roadway. After stabilizing the retaining roadway, the force of the reinforced anchor cable was stabilized at 225 kN, which was 39% of the tensile strength of the anchor cable. The anchor cable was in a good stress state and met the requirements for supporting the retaining roadway roof.  
Figure 8: Changes in force on anchor cables in the lagging working face.  
Figure 9: Changes in displacement of top and bottom plates of the lagging working face.  
In Figure 9, it can be seen that the top plate sank rapidly after a 60 m lag in the working face, and the movement of the top plate tended to stabilize around 150 m behind the working face. After stabilizing the roadway, due to the withdrawal of the temporary reinforcement support, there was a slight subsidence of the roof, with a maximum subsidence of about 260 mm on the cutting seam side. The position in the roadway remained stable at around 160 mm, and the subsidence on the coal pillar side was the smallest, approximately 80 mm.  
The control situation of the roadway roof during the retention period is shown in Figure 10. The stress on the reinforced anchor cables and the deformation of the roadway roof during the comprehensive retention period could be determined. The stability of the roof during the top-cutting retention period was good, and the section of the retained roadway met the usage requirements. This verifies the pressure relief effect of the top-cutting parameters and the rationality of the design.