# Anisotropy and Directivity Effects on Uniaxial Compression of Carbonaceous Slate Form Jinman Mine
## 3 Results and Discussion
### Failure Characteristics  
#### 3.4.1 Macro-Fracture Mode Characteristics  
The failure mode and fracture shapes reflect the failure mechanisms directly for different loading conditions. It not only directly reflects the stress distribution during the loading process but also indirectly reflects the effects of differences in the degree of development, mineral composition, and internal defects of the internal structure on the overall strength. In particular, for slate rock with plate-like structures, in a weathered state, there are significant anisotropic characteristics in the rock interior. Its complex stress state can easily lead to floor heave and slabbing failure in roadways. To study the failure mode and fracture characteristics, Figures 9-12 show the fracture distribution under vertical and parallel loading. Combined with the results of uniaxial compression tests, the brittleness and ductility of rock samples can be divided by the axial peak strain [29]. For a uniaxial peak strain of less than 1%, the rock samples show brittle failure. For a uniaxial peak strain in the range of 1% to 5%, the rock samples show brittle and ductile failure. For a uniaxial peak strain greater than 5%, the rock samples show ductile failure. Tables 1 and 2 show that when the axial stress is perpendicular to the slate structure, the peak strains of the gray samples and the carbonaceous samples are 1.24\(-\)2.97%, and 1.09\(-\)2.05%, respectively. When the axial stress is loaded parallel to the slate structure, the peak strength of gray samples and the carbonaceous samples are 3.27\(-\)6.26%, and 1.29\(-\)1.58%, respectively. Therefore, the peak strains of gray and carbonaceous samples are less than 1.00%, and the slate rock show brittle failure. Figure 11: Fracture distribution of gray samples under parallel loading: (**a**) No. 1 sample; (**b**) No. 2 sample; (**c**) No. 3 sample; (**d**) No. 4 sample. Figure 10: Fracture distribution of carbonaceous samples under vertical loading: (**a**) No. 1 sample; (**b**) No. 2 sample; (**c**) No. 3 sample; (**d**) No. 4 sample. Figure 9: Fracture distribution of gray samples under vertical loading: (**a**) No. 1 sample; (**b**) No. 2 sample; (**c**) No. 3 sample; (**d**) No. 4 sample. Figures 9 and 10 show that when the axial stress is loaded perpendicular to the slate structure, the failure modes of the gray and carbonaceous samples are oblique shear fracture, and shear fractures on the surface of the slate sample were observed. Compared with the carbonaceous samples, when the gray samples undergo shear failure, they are also prone to bursting and ejecting rock blocks, forming missing areas and which aggravate the fragmentation of the slate sample surface. The broken areas are mostly located near the primary shear fractures, as shown in Figure 9a. This is because the quartz content in gray slate is significantly more than that in carbonaceous slate, and the increase of quartz minerals aggravates brittle deformations of rock samples [29; 30; 31]. Due to the differences in the mineral content of rock samples, only one main shear fracture appears on the surface of the gray samples, and the fracture length is about 70.00-75.86 mm. There are 2 to 3 microfractures in the shear fracture and the fragmented edge of the carbonaceous samples, and the angle between microfracture and shear fracture is 38\({}^{\circ}\)\(-\)45\({}^{\circ}\). The appearance of broken areas and microfractures aggravate the rate of dilation speed of the slate samples. It should be pointed out that the fragmented area of the No.4 carbonaceous sample is a fragment formed by the rock sample falling and hitting the ground after shearing failure, as shown in Figure 10b. Figures 11 and 12 show the fracture distributions of gray and carbonaceous samples under parallel loading, respectively. They show that axial stress has a significant impact on failure modes. Figure 11 shows that the fracture mode of the gray samples is mainly splitting failure, and segregation appears in the slate structures under parallel loading.