## 3 Results and Analysis
### Analysis of Surface Settlement before Different Treatment Methods in Goaves  
The surface subsidence curve depicted in Figure 6a illustrates that prior to the treatment of goat No. 3 (2015-2018), it exhibited a concave shape, with accelerated subsidence rates observed at both ends in comparison to the middle, resulting in two distinct subsidence basins. Specifically, the recorded surface subsidence rates for A1, A2, A3, and A4 were as follows: 144.58 mm/year for A1; 85.33 mm/year for A2; 136.12 mm/year for A3; and 159.06 mm/year for A4. Upon comparison, it becomes evident that the subsidence rate of A1 is approximately 36% higher than that of A2. Under conditions characterized by an unstable roof but stable pillars, the surface subsidence rate increases proportionally with mining depth while prominent subsidence basins manifest in areas with greater depths of excavation. In addition, A4 exhibits a 17% faster subsidence rate than A3 due to a more significant presence of unstable pillars, leading to more concentrated surface subsidence rates and distinct subsidence basins centered around these unstable pillars. The presence of stable pillars interspersed among the unstable ones will effectively mitigate surface subsidence. However, if the spacing between these pillars is insufficient and their quantity is limited, the mitigation effect may not be significant, resulting in the formation of a substantial subsidence basin.  
The surface subsidence curve prior to the treatment of goat No. 6 (2015-2018) exhibited an obliquely serrated pattern, characterized by four distinct subsidence basins, as depicted in Figure 6c. The corresponding subsidence rates for B1, B2, A3, B4, and B5 on the surface subsidence curve were recorded as 85.92 mm/year, 95.40 mm/year, 119.22 mm/year, 85.76 mm/year, and 144.79 mm/year, respectively. Through comparative analysis, it was observed that the subsidence rate of B2 exceeded that of B1 by approximately 17%, indicating a correlation between surface subsidence and pillar width-height ratio, specifically implying that a smaller width-height ratio resulted in higher surface subsidence rates. The subsidence rate of B3 and B5 demonstrates a 51.6% increase compared to that of B1 and B2, indicating a positive correlation between the surface subsidence rate and the slope span. A larger slope span leads to an accelerated surface subsidence rate, while a smaller slope span results in reduced subsidence. Notably, the subsidence rate exhibits a decrease between B1 and B2, B2 and B3, and B3 and B5 due to the presence of stable pillars amidst unstable ones, effectively exerting control over local surface subsidence. Moreover, an augmented number of stable pillars leads to a more pronounced deceleration in the surface subsidence rate.  
The analysis of Figure 6e reveals that the pre-treatment surface subsidence trend in goat No. 2 exhibits a central region characterized by rapid subsidence rates, gradually decreasing toward both sides, resulting in a concave-shaped curve. Specifically, the measured surface subsidence rates at C1, C2, and C3 are 78.84 mm/year, 85.02 mm/year, and 89.28 mm/year, respectively, on the subsidence curve. A comparison between the positions of C1 and C2 indicates that as one moves farther away from the unstable pillar, there is a corresponding decrease in the rate of surface subsidence observed. Notably, among all analyzed points, C3 demonstrates the highest subsidence rate, thus suggesting that when only a single pillar experiences instability while maintaining stability within the goat area's roof structure, overall subsidence remains relatively minor with its center located around unstable pillars.