*2.2. Field Tests*

In order to study the deformation degree of the roadway enclosure, the 30503 return roadway repair, at the section at about 240 m~840 m, was selected, and the roadway surface displacement observation points were laid out within this area. One observation point was arranged every 40 m, with a total of 16 observation points, numbered 1~16. Short-term observations were carried out for 10 days, and the observation data of the 3rd, 7th, and 10th days were taken. Based on the data of the first measurement, roadway deformations at different mileages were calculated for each measurement, and the measured data are shown in Figure 2.

According to Figure 2a, it can be seen that, on the 3rd day of the test, the maximum value of top plate displacement is located at 280 m of the dug-in section, which is 24 mm, and the maximum value of the two gang displacements is located at 680 m of the dug-in section, which is 4 mm. According to Figure 2b, it can be seen that on the 7th day of the test that the repaired section of the roadway showed extensive deformations; here, the maximum value of top plate displacement is located at 440 m of the dug-in section, which is 34 mm. The maximum amount of top plate displacements is located at 440 m of the excavated section, reaching 34 mm, and the top plate displacement increased by 3 mm compared with the measured value at 280 m of the excavated section on the third day and by 35 mm compared with the measured value at the same point on the third day; the maximum amount of the displacement of both gangs is located at 680 m of the excavated section, reaching 61.5 mm, and the displacement of both gangs increased by 9 mm compared with the measured value at 680 m of the excavated section on the third day and by 49.5 mm compared with the measured value at the same point on the third day. After 4 days, significant deformations occurred at the same measurement point. According to Figure 2c, it can be observed that on the 10th day of the test, the deformation

phenomenon of the repaired section of roadway still existed and spread, among which the maximum amount of top plate displacement was located at 400 m of the dug-in section, reaching 35 mm; this is an increase of 5 mm compared with the measured value at the same point on the 7th day. The maximum amount of two gang displacement was located at 760 m of the dug-in section, reaching 66 mm, an increase of 4.5 mm compared with the measured value at the same point on the 7th day. Although the periodic deformation at the same measurement point is less than the amount of displacement in 3–7 days, there is still deformation and a growing trend.

**Figure 2.** Figure for 30503: ventilation roadway. (**a**) Day 3 alleyway deformation. (**b**) Day 7 alleyway deformation. (**c**) Day 10 alleyway deformation.

In summary, within 10 days, the 30503 return roadway repair section had top plate sinkage changes within the range of 3~35 mm. The two gangs moved closer at a range of 0~66 mm, and the displacement of the two gangs is significantly larger than the top plate's displacement. The same measurement point, the two gangs' displacement, and the top plate's displacement also have obvious differences. The roadway exhibited obvious non-uniform damage phenomena. To control the deformation and damage of the roadway and avoid accidents, the following is an analysis of the extent of damage to the plastic zone and the degree of deformation of the surrounding rock under different arrangements of the roadway from both vertical and horizontal directions. The distribution rules of stress and the plastic zone in the surrounding rock of the 30503 roadway along the top slab, along the bottom slab, along the top left and bottom coal slab, differently sized coal pillars, and the area located directly below the residual coal pillars are analyzed. Based on the above analysis, reasonable arrangements and the arrangement principles of the residual coal pillar's lower return roadway are determined. The diagram for different roadway layout schemes is shown in Figure 3, and the dashed line in the figure denotes the limit of coal pillar retentions for different horizontal roadway layout schemes; from right to left, the coal pillars are 4 m, 8 m, 15 m, 20 m, and 25 m.

**Figure 3.** Schematic diagram of different roadway layout schemes.
