## 5 Industrial Field Test
### Field Observation and Maintenance Effect  
The mine pressure at the tested segment of the return air subinclined shaft under the new support was monitored by the cross-shaped point distribution method using the borehole imager and bolt-cable dynamometer. The results were compared with those in the original scheme as follows. (1) Borehole observation of the surrounding rock. The borehole images observed on the roof under the original support are presented in Figure 13. It can be seen that annular cracks are found at 0.47 m, 0.72 m, 0.91 m, 1.27 m, 1.48 m, 1.59 m, 2.14 m, 2.16 m, 2.75 m, 2.84 m, and 5.01 m; vertical cracks are developed at 1.0 m, 1.21 m, 1.91 m, 2.0 m, 2.31 m, and 4.85 m, which can easily result in the formation of abscission layers or even fracture zones. Abscission layers are formed at 2.38 m, 2.59 m, 2.65 m, and 2.84 m; longitudinal holes are observed within 1.22-1.34 m. The continuous fracture zones are distributed from 2.38 m to 2.43 m, with the longest one reaching 5 cm, where the cracks are developed at a maximum depth of 5.01 m. In the original scheme, the surrounding rock on the roof has poor integrity, developing numerous cracks, abscission layers, and continuous fracture zones. The cracks, with a maximum depth of 5.01 m, tend to extend deeper. This scheme has an extremely poor maintenance and control effect on the roadway. According to the borehole images observed on the roof under the new support (Figure 14), minor and annular cracks are formed at 0.13 m, 0.68 m, 0.87 m, and 1.19 m, and there are cracks filled with slurry at 1.9 m. This indicates that the basic thick-layer anchorage can inhibit the generation and propagation of initial rock cracks and guarantee the strength of the initial support. Meanwhile, cracks are plugged with slurry to rebond the surrounding rock into an integral whole, which not only improves the overall strength of the fractured rock mass but also significantly enhances roadway stability. (2) Axial force monitoring of bolts and cables. Figure 15 shows how the axial force of bolts and cables evolves in the original scheme and how the axial force of bolts, cables, and grouting cables evolves in the new scheme. According to the observation on mine pressure, the axial force of bolts and cables includes two parts: one refers to the pre-tightening force applied during the installation of bolts and the other is the axial tension on bolt rods caused by surrounding rock deformation. Therefore, how the rock mass evolves in deep and shallow strata can be obtained by observing the change of this axial force. After the pre-tightening operation is finished, the axial force of bolts in the original scheme is 48 kN. Then, the value surges to 178.22 kN and is finally stabilized at 177.25 kN, as shown in Figure 15a. The axial force of cables is 105.96 kN after this operation, and then it gradually rises over time, during which there is a phenomenon of sudden increase and decrease caused by the fracture of rock mass on the surface. It can be observed that the axial force of bolts rises, which indicates the severe deformation of shallow rock mass, manifesting as the formation of abscission layers and the propagation of cracks. By contrast, the axial force of cables increases gradually, which implies that the deep rock mass expands and deforms slightly at a low speed. These results are consistent with the image data obtained from borehole observation. Figure 15b shows that the axial force of bolts in the new scheme is 68.59 kN after pre-tightening. Then, it gradually rises to 103.03 kN. The axial forces of ordinary and grouting cables are 163.09 kN and 106.16 kN, respectively, after pre-tightening. Then, the values slowly increase to 185.55 kN and 174.79 kN, respectively. The slow growth of this force in bolts, cables, and grouting cables proves the gradual expansion and small deformation of deep and shallow surrounding rocks under the new support.