## 4 Experimental Procedure
### Model Loading Procedure  
The model is subjected to longitudinal loading using a top hydraulic cylinder, with a total of 20 loading cycles, accumulating a load of 15 kN. To ensure the stability of the model under load, the first eight loading cycles increase by 0.5 kN each, while the remaining cycles increase by 1 kN each, as shown in Figure 6.  
Data from the instruments are collected before loading and after the loading stabilizes. The data include measurements from the dial gauge, total station, 108-channel pressure sensors, anchor rod load cells, and pressure sensors at the base of the single support pillar. During the first nine loading cycles, with a cumulative load of 5 kN, it was observed that although a few irregular fine cracks appeared in the overburden rock, and a tendency for roof subsidence, no delamination occurred, and the surrounding rock of the opening cut showed no significant damage. Figure 5: Excavation and support process of the opening cut: (**a**) schematic diagram of opening cut excavation, (**b**) step one of excavation, (**c**) step two of excavation, (**d**) step three of excavation, (**e**) step four of excavation, (**f**) complete support with anchor rod (cable), (**g**) installation of single support pillar, (**h**) installation of dial gauge, (**i**) model prepared before loading. During the 10 th loading cycle, with a cumulative load of 6 kN, damage began to occur at the left side corner of the opening cut, resulting in a crack measuring 3.2 cm in length, oriented at a 60\({}^{\circ}\) angle to the roof. Although no delamination was observed in the roof, the number of fine cracks in the overburden rock increased. As the loading progressed, the crack at the side corner of the opening cut gradually widened, and signs of delamination, loosening of both sides, development of cracks, and roof subsidence became apparent. With the increase in loading cycles, the delamination continued to expand, the loosening of the sides increased, cracks continued to develop, and damage occurred at the bottom corners of the sides, accompanied by coal spalling. During the 12 th loading cycle, with a cumulative load of 8 kN, localized failure and minor loosening zones were observed in both sides of the opening cut. The left side exhibited a loosening zone extending 2.4 cm from the opening cut, while the right side showed a 3.4 cm wide loosening zone. Additionally, localized spalling occurred at the right side, accompanied by minor coal fragmentation. A progressive delamination (1 cm thick) was detected in the immediate roof strata, indicating an ongoing subsidence tendency of the roof. During the 15 th loading cycle, with a cumulative load of 11 kN, the cracks on the left and right sides of the incision continued to develop, with a loosening range of 4.4 cm on the left side and 4.1 cm on the right side. The bottom corner of the left side was damaged, with a small amount of coal peeling off and the roof continuing to sink. By the 19 th loading cycle, with a cumulative load of 15 kN, it was observed that cracks on both sides of the opening cut continued to develop. The loosened area on the left side expanded to 5.5 cm, while the right side reached 5.0 cm, with severe surface damage evident on both sides. There was a sudden increase in the amount of displacement, indicating a potential for imminent collapse. The first layer of rock above the roof, located between 22.5 cm and 33.3 cm from the left side, experienced fracturing, leading to a sudden increase in delamination and a risk of roof fall. Additionally, the single support pillar at the first support cross-section on the right side underwent severe bending deformation, ultimately resulting in failure due to compression, as shown in Figure 7. The physical simulation results demonstrated that the roof subsidence (24.071 mm) and sidewall convergence (23.478 mm) in the opening cut exhibited significantly close magnitudes, indicating a synergetic deformation mechanism between the roof and sidewall under mining-induced stresses.