# Cataclastic Characteristics and Formation Mechanism of Dolomite Rock Mass in Yunnan, China
## 4 Conclusions  
This paper uses in-hole television, borehole shear wave velocity tests, borehole cores, 3D laser scanning techniques, image processing techniques, and SEM to analyze the macroscopic and microscopic structural characteristics of the fractured rock masses from both rock blocks and rock discontinuities qualitatively and quantitatively and draws the following conclusions. 1. Within the depth range of the borehole exposures, the degree of fragmentation of the rock mass generally decreases with increasing depth, the decrease is not significant, and differential fragmentation occurs locally, but the rock mass is generally fragmented. Most borehole cores are fragmented and fractured, with a basic RQD value of 0 and a basic rock quality grade of V. Part of the borehole cores are block fractured, with an RQD value of less than 10% and a basic rock quality grade of IV. These can provide a basis for rock mass classification. According to the Geological Engineering Handbook [1], the rock quality designation is very poor. 2. The shear wave velocity can be used to estimate the integrity of the rock mass and determine the site classifications. The shear wave velocity of the dolomite on the high slope generally increases with the depth of the borehole, but the increase is very small. Part of the shear wave velocity has a tendency to decrease, and the integrity of the rock mass should be broken or very broken. According to GB 50011 (2010) [25], the site classification of YPP is Level I\({}_{1}\). 3. The rock structure revealed by the excavation section is fragmented, the degree of rock mass integrity is fragmented, and the rock structural type is mainly fractured. The degree of fragmentation varies from one rock layer to another. The thinner the rock layer is, the smaller the spacing of the muddied interlayer is; that is, the closer it is to the muddied interlayer, the more fragmented the rock mass is. The discontinuities are mainly facies, muddied inclusions, bedding joints, and shear joints, some of which are slightly staggered along the bedding joints. The joints are straight, smooth, interconnected, and largely unfilled, with each set of joints parallel to each other. The discontinuities are extremely well developed, with fracture spacing at the centimeter level, some even less than 1 cm. The discontinuities can be divided into six sets, the first set being muddied interlayer, the second set being bedding joints, and the remaining four sets being shear joints. The unloading effect generated by excavation causes the slope to slide along the bedding joints and muddied interlayer, leading to the failure of the support systems. 4. The angles of the blocks of different grain sizes are sharp, and the overall angularity of the blocks is more evident than that of the cubes, with roundness being angular and sharp-angled. The discontinuities are flat and smooth; each block has multiple sets of mutually parallel discontinuities. The smaller the blocks, the more complex the surface morphology. The angular and sharp-angled blocks indicate that tectonics mainly control dolomite fracturing. 5. Scanning electron microscope observations show that the ultra-micro fractures are not flat and smooth, the fractures are folded, and the fracture opening is mainly on the micron scale. The fractures do not cut through the crystals but mainly split along the intercrystalline and crystal interfaces, and the crystal structure on both sides of the fracture is intact. These ultra-micro fracture features also indicate that the fracturing of dolomite is mainly controlled by tectonics and almost unaffected by surface weathering. 6. Chemical weathering is not the main mechanism of dolomite fragmentation. The fracturing of dolomite is mainly related to the original sedimentary construction and tectonics. **Author Contributions:** Conceptualization, L.T., W.L. and J.Z. ; methodology, J.Z. ; software, H.G. ; validation, L.T. and H.G. ; formal analysis, L.T. ; investigation, L.T. and J.Z. ; resources, W.L. ; writing--original draft preparation, L.T.