# Cataclastic Characteristics and Formation Mechanism of Dolomite Rock Mass in Yunnan, China
## 3 Results and Discussion
### Macroscopic Fracture Characteristics of Rock Mass
#### 3.1.3 Analysis of Typical Excavation Profile  
The dolomite exposed in the excavation profile is generally very fractured (Figure 6). Consistent with the results of in-hole television images and borehole shear wave velocity analysis, the excavation profile also shows the presence of localized differential fracturing. The profile exposes six layers of muddied interbeds with small interbed spacing between 9.3 cm and 16.7 cm. The rock masses between the interbeds are all very fractured, while the thicker dolomite rock masses (up to 0.8 m thick or more) above interbed L1 are more intact than those in the lower part (Figure 6a,c). However, the closer the proximity to interbed L1, the more fractured the rock masses become (Figure 6b). The degree of fragmentation is also inconsistent between interlayers L1 and L6, and the most fragmented rock is between L4 and L5 (Figure 6d), which may be related to the fact that the spacing between L4 and L5 is the smallest. Figure 5: Shear wave velocity histogram of three boreholes. (a) ZK01. (b) ZK13. (c) ZK28. The velocity is different in filled soil and dolomite. The rock discontinuities are well-developed and dominated by facies or muddied intercalations and shear joints. Figure 6c shows two significant sets of shear joints which are flat, smooth, and interconnected. The rock between interlayers L2 and L3 is mainly cut by two sets of subcritical joints (Figure 6e), straight, smooth, spaced about 1 cm apart, and interconnected. The rock between interlayers L3 and L4 is mainly cut by three sets of joints (Figure 6f). The first set of joints (J\({}_{1}\)) has an NW-SE strike. The second set of joints (J\({}_{2}\)) has an NE-SW strike. The third set of joints (J\({}_{3}\)) has an E-W strike. All three sets of joints are flat, smooth, and interconnected, each parallel to the other, and spaced at the centimeter level, with J\({}_{3}\) being less dense than J\({}_{1}\) and J\({}_{2}\). Figure 6g shows the two main shear joints with smooth, flat nodal surfaces. Figure 6h shows a set of suberet shear joints. The joints are straight, smooth, parallel to each other, unfilled, and spaced less than 2 cm apart in addition to the feather-decorated tensor nodules. A geological compass and a 3D laser scanner were used to measure 40 sets of the strike-dip directions of discontinuities in three sections of the observation site, of which 8 were muddied interlayers and 32 were shear joints. According to Figure 7, the discontinuities at the observation site can be divided into six sets. The first set comprises muddied interlayers with an average dip at 23\({}^{\circ}\) and an average dip direction at 200\({}^{\circ}\). The second set comprises bedding joints with a dip and dip direction similar to the muddied interlayers. The third set  
Figure 6: Photos showing the macro fragmentation characteristics of dolomite in an excavation profile. (**a**) Overall photo of dolomite and discontinuities. (**b–i**) Detailed photos. L1–L6: six layers of muddied interbeds. J\({}_{1}\)–J\({}_{3}\): three sets of joints. 53\({}^{\circ}\)\(\angle\) 86\({}^{\circ}\): dip direction \(\angle\) dip. comprises shear joints with an NE-SW strike and a dip of 85\({}^{\circ}\). The fourth set comprises shear joints, with an average dip at 81\({}^{\circ}\) and an average dip direction at 67\({}^{\circ}\). The fifth set comprises shear joints with an average dip at 66\({}^{\circ}\) and an average dip direction at 34\({}^{\circ}\). The sixth set comprises shear joints with an average dip at 52\({}^{\circ}\) and an average dip direction at 356\({}^{\circ}\). During excavation construction, the high slope was destabilized three times. The retrogressive rockslide occurred along the bedding planes and the mudded interbeds, which were nearly paralleled to the slope face. Materials in the mudded interbeds were extruded during the slide. In summary, the rock structure at the observation site is very fragmented. The degree of fragmentation varies from one formation to another.