4.3.1. Scheme of Reinforcement Support

Impacted by the mining, rib spalling and support failure were observed in the roadway. According to the above study, the depth of plastic failure in the surrounding rock of the 42202 auxiliary transport roadway after being disturbed by the first stope mining gradually exceeds the range of bolt support, and the bolt support of the two ribs has basically failed during the secondary stope mining. Thus, it is necessary to strengthen the support of the two ribs. According to the principle of asymmetric support, the solid coal rib was supported with 28.6 mm × 6500 mm anchor cables, and two rows of anchor cables with a spacing of 2000 mm were installed at the rib part together with 300 × 300 × 16 mm pallets. The coal pillar rib was first supported with 22 mm × 6500 mm anchor cables, and two rows of anchor cables with a spacing of 2100 mm were added together with 4600 × 140 × 8 mm π-steel strips. In addition, a row of 28.6 mm × 6500 mm anchor cables with a spacing of 2100 mm were added together with 4600 × 140 × 8 mm π-steel strips, as shown in Figure 13.

**Figure 13.** Cross-sectional view of the reinforcement support of the two ribs of the roadway.

In order to verify the stability control effect of bolting support technology on 42202 transportation roadway, the plastic zone state of surrounding rock before and after bolting support was compared by numerical simulation software, as shown in Figure 14. According to Figure 14b, when the width of the coal pillar is set as 25 m and anchor cable reinforcement support technology is adopted, the plastic range of the two walls of surrounding rock is 2.0 m at most. Compared with that before support, the plastic zone of the coal pillar is reduced by about 1.5 m and the solid wall is reduced by about 1.0 m. It can be seen that the use of anchor cable reinforcement support can effectively prevent the plastic destruction of surrounding rock and fully ensure the stability of the mining roadway.

**Figure 14.** Numerical simulation verification of anchor cable reinforcement support effect. (**a**) Schematic Diagram of Anchor Cable Reinforcement and Support. (**b**) Distribution of plastic zone of surrounding rock before anchor cable reinforcement. (**c**) Distribution of plastic zone of surrounding rock after anchor cable reinforcement.

#### 4.3.2. Displacement Monitoring of Roadway Surface

Based on the sectional coal pillar retaining scheme and the roadway surrounding rock anchor reinforcement support technology proposed in this paper, the experiment was carried out in the 42202 mining roadway. Multiple on-site full-section scanning monitoring tasks were conducted on the 42202 auxiliary transport roadway directly below the skip mining coal pillar during the second stope mining. The results are shown in Figure 15, where the roadway deformation remains basically the same as the working face advances. In the meantime, no significant mine pressure behaviors, including large deformation, rib spalling, and roof fall, are observed at the site, as shown in Figure 16. Therefore, the adopted control techniques can well control the destabilization of the roadway below the remaining coal pillar after multiple mining processes, thus ensuring safe and efficient production at the working face.

**Figure 15.** Full section scan of the roadway.

**Figure 16.** Field observation of roadway stability.

#### **5. Conclusions**

(1) Affected by the T-shaped remaining coal pillar in the 2-2 coal seam, the vertical stress at the stope mining roadway of the underlying 4-2 coal seam increased sharply, reaching a stress concentration coefficient of up to 1.4 times. In addition, the superimposed effect of lateral high abutment pressure generated during stope mining at the 42201 working face caused great deviatoric stress in the coal mass, and the radius of Mohr's circle of the stress increased significantly. After roadway excavation and unloading, the surrounding rock is prone to wide-range compression-shear failures. Thus, the peak lateral pressure area should be avoided.

(2) Based on the on-site engineering conditions, numerical simulation software was applied to obtain the stress characteristics and plastic area development pattern in the surrounding rock of the 42202 stope mining roadway below the T-shaped remaining coal pillar. As the width of the sectional coal pillar in the 4-2 coal seam increased, the stress curve of the surrounding rock shifted from single-peaked to asymmetrically double-peaked, and the stress concentration coefficient gradually decreased. Meanwhile, the stress difference between the two ribs of the roadway showed a decreasing trend, and the failure mode of the coal pillar changed from penetrating failure to only producing a 2.5 to 3.0 m plastic area. The large vertical stress increase in the surrounding rock was the main reason for the failure and destabilization of the roadway.

(3) Considering the high-stress area under the T-shaped remaining coal pillar, the sectional coal pillar width in the 42202 mining roadway is 25 m. In the meantime, the asymmetric reinforcement anchor cable support technology for both sides of the roadway is proposed. Based on the numerical calculation verification, it is believed that the scheme reduces the plastic zone of surrounding rock by 1.0–1.5 m, which can effectively maintain the stability of the roadway.

(4) On-site industrial testing showed that the roadway deformation of the 42202 stope roadway was small and basically constant, and no rib spalling or roof fall was observed, thus achieving the stability control of the stope mining roadway below the remaining coal pillar.

**Author Contributions:** All authors contributed to this paper. Conceptualization, Q.F. and K.Y.; methodology, Q.F.; software, Y.W.; validation, Q.F. and Z.W.; formal analysis, Q.L.; data curation, Q.F.; writing—original draft preparation, Q.F.; writing—review and editing, Q.L. and K.Y.; validation, X.H. and Q.L.; funding acquisition, K.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by the Collaborative Innovation Project of Universities in Anhui Province (GXXT-2019-029), the Institute of Energy, Hefei Comprehensive National Science Center under Grant (No. 21KZS215), Major special projects of science and technology in Shanxi Province (No. 20191101016), Open Research Grant of Joint National-Local Engineering Research Centre for Safe and Precise Coal Mining (Grant NO. EC2021014).

**Data Availability Statement:** The data used for conducting classifications are available from the corresponding author authors upon request.

**Conflicts of Interest:** The authors declared no potential conflict of interest with respect to the research, authorship, and publication of this article.
