**2. Asymmetric Deformation Characteristics of a Roadway in a Steeply Inclined Coal Seam** *2.1. Basic Overview of the Roadway*

Located in Guangyuan City, Sichuan Province, China, the Zhaojiaba Coal Mine, as shown in Figure 1a, is within the mining range of the Sichuan Coal Industry Group Limited Liability Company. The mine is a typical steeply inclined thin coal seam. At present, the main area undergoing mining is Mining Area 106, and the buried depth of the working face is 350–600 m. The roadway currently being excavated is the ventilation roadway of Working Face 1961, which is 15 m horizontally and 20 m vertically from the upper goaf. This roadway, a typical one in the steeply inclined coal seam, is excavated along two steeply inclined coal seams, i.e., 9# coal seam and 10# coal seam. The average dip angle of the two coal seams is 53◦, the thickness of 9# coal seam is 1.1 m, and the thickness of 10# coal seam is 1.0 m, both of which are thin coal seams. The rock stratum between the two coal seams is carbonaceous mudstone with a thickness of 2.5 m. The ventilation roadway of

Working Face 1961 is 850 m long, and always crosses the two coal seams. The rock stratum histogram of the roadway is shown in Figure 1b.

#### *2.2. Primary Support Scheme*

According to the engineering experience, the ventilation roadway of Working Face 1961 adopts the vertical wall irregular top section, with the roadway width being 4.00 m and the roadway height being 3.55 m, as shown in Figure 2. The coal–rock mass is cut in parallel to the immediate roof of 9# coal seam without damaging the rock mass structure of the immediate roof, and the roof on this side is a straight inclined roof; the coal–rock mass is then cut perpendicularly or obliquely to 9# coal seam and the mudstone interlayer to form an arc roof, and the roof on this side is curved.

**Figure 2.** Irregular roadway section and primary support form.

As shown in Figure 2, the primary support of the ventilation roadway of Working Face 1961 is in the form of a bolt–anchor cable combined support, for which 11 bolts with a specification of Φ20 × 2200 mm are installed in each row, with the bolt spacing and row spacing being 800 mm × 800 mm and the bolts being connected by reinforced ladder beams. Five anchor cables with a specification of Φ17.8 × 7000 mm are installed in each row, with the anchor space and row spacing being 1600 mm × 1600 mm and the front as well as rear anchor cables of every two rows being supported by I-beams. The full section of the roadway is provided with a rhomboid metal mesh to protect its surface. Each bolt is matched with two K2335 anchoring agents, and each anchor cable is matched with five K2335 resin cartridges. On-site measurement feedback shows that the pre-tightening force of the bolt in the primary support is only 30 kN and that the pre-tightening force of the anchor cable is only 80 kN.
