## 3 Analysis of Results
### Mechanical Principle of Zonal Disintegration  
Besides the physical analog modeling and numerical analysis of zonal disintegration, its mechanical mechanisms were also widely explored. [PERSON] et al. revealed the existence of unloading waves in deep strata after the excavation of high-stress strata, thereby inducing discontinuous fracturing of the surrounding rocks in the roadway [19]. [PERSON] et al. analyzed the stress field evolution of the surrounding rock based on the pressure fluctuation at the inner wall of the roadway to explore the alternate manifestation patterns of fractured and intact zones [20,21]. Based on the energy conversion characteristics of deep rocks, some scholars have analyzed the mechanical principle of zonal disintegration by modifying the conventional elastoplastic model [22,23]. [PERSON] et al. performed a theoretical exploration of fractured and intact zones in the roadway based on damage mechanics and non-Euclidean geometry [24]. Other studies mostly focused on the heterogeneity and discontinuity of rock masses. Thus, using the rock strength-related parameters that obeyed  
Figure 10: Vertical stress variation in the roadway floor versus distance to the roadway. the Weibull distribution law, [PERSON] et al. designed a nonuniform strain-softening model of rocks and obtained annular zonal disintegration results via numerical simulation [14]. The factors of interest in each mechanical mechanism or model can lead to non-homogeneous rock mass damage. Accordingly, scholars hold different opinions regarding zonal disintegration mechanisms. The disputes on the zonal disintegration mechanism essentially lie in the fact that the alternate appearance of disintegration and intact zones in the annular pattern was speculated based on limited measurement results. Despite the alternate occurrence of fractured and intact zones that could be observed in multiple drilling holes of the same roadway section, the stressed state of these zones between boreholes was unknown. The existing empirical model was obtained by collocating them in the order of their occurrence [8]. At the same time, the scientific validity of this data-processing method has not been effectively confirmed in the laboratory. [PERSON] et al. constructed the characteristic lines of the roadway perimeter based on the elastoplastic flow theory and pointed out that the zonal disintegration can be obtained by reproducing the cave shape using a family of characteristic lines [24], as shown in Figure 11. Based on the actual measurement results of [PERSON] [25], [PERSON] et al. reported that the zonal disintegration occurred in a circular damage zone, with a certain distance (spacing) between damaged zones and a circular intact zone between adjacent damaged zones. Moreover, the neighboring disintegration regions were separated by annular intact ones, while slip or failure lines intersected to a certain degree, which was not consistent with the actual condition of zonal disintegration. According to field measurements, not all disintegration zones were annular or completely separated from each other. Figure 12a shows the measured results in [25], where different numbers of disintegration zones can be observed in the drilling holes 2, 3, 4, and 5, suggesting fairly complex spatial relationships between fractured zones. The data in [5] can also validate the measured results (see Figure 12b). Figure 11: Characteristic lines constructed via the elastoplastic flow theory. (**a,b**) denote different types, respectively. Figure 12: Measured results on zonal disintegration: (**a**) measured results in [25]; and (**b**) measured results in [5]. The following conclusions can be drawn from the above numerical simulation results: Firstly, the fractures in the surrounding rocks gradually developed from the roadway surface to deeper parts. Secondly, the fracture planes developed towards the deep surrounding rocks from the free plane (the roadway surface), forming an enclosed fracture loop around the roadway.