# Effects of Water-Soaking Height on the Deformation and Failure of Coal in Uniaxial Compression
## 3 Results and Discussion
### Local Strain Characteristics  
In order to further study the deformation characteristics of different soaking heights coal specimens during compression, the local strain at different positions of the coal specimens was monitored by the CM-2B strain monitor. According to the setting of the strain rosette at the beginning of the test, local strains at heights of 25 mm, 50 mm, and 75 mm from the bottom of coal specimens were analyzed. The local strain development for specimens with different soaking heights is presented in Figure 10a-e. To gain a deeper understanding of the local strain, the time-stress curves of specimens with different soaking heights are also shown by the black curves. Figure 10: Evolution of the axial stress and local strain for different soaking heights specimens at different loading times. (**a**) 0 mm water-soaking height; (**b**) 25 mm water-soaking height; (**c**) 50 mm water-soaking height; (**d**) 75 mm water-soaking height; (**e**) 100 mm water-soaking height. It can be seen from the axial strains at different positions of coal specimens that the local strains of coal specimens with water-soaking height of 0 mm, 75 mm, and 100 mm were relatively consistent at different positions during the loading process. It shows that the deformations of the upper, middle, and lower layers of the coal specimens were synchronized, and the whole exhibited uniform deformation characteristics during the loading and deformation of the three groups of coal specimens. In the 25 mm and 50 mm water-soaking height groups, the local strains at different positions were quite different. At the initial stage of loading, different deformation amplitudes were exhibited, and the overall deformation exhibited uneven characteristics. For the coal specimens in the 25 mm water-soaking height group, along the height of the coal specimens, the local strain at 25 mm height was the most significant, while the strains at 50 mm and 75 mm height were relatively flat, and the changes between the two positions were not much different. For coal specimens in 50 mm water-soaking height groups, along the height of the coal specimens, the strains at 25 mm and 50 mm were more significant, and the variation amplitudes of the two were not much different, while the strain at 75 mm was relatively flat. From the perspective of local strain changes, water soaking had a significant effect on the deformation of coal specimens. For coal specimens immersed in water of 25 mm height, the coal specimen was in full contact with water below 25 mm height. The softening effect of water on the coal specimen at this part was obvious. During the loading process, the strain changed greatly. The moisture content of the coal specimens at 50 mm and 75 mm was less than 25 mm, the corresponding strain changes were small. The softening effect of water on the coal specimen was obvious through experiments. On one hand, because the coal specimen was immersed in water, the friction between the coal particles was weakened. On the other hand, due to the existence of capillary force and pore pressure, the water-soaked coal specimen produced more microcracks, which made the overall strength of the coal specimen weak. The softening extents of different layers of coal specimens were different, the extents of deformation of the corresponding layers were different, resulting in nonuniform deformation of the overall coal specimens. In previous studies, the water content was taken as an absolute value to investigate the mechanical properties of water-bearing coal specimens under different water contents. Through this experiment, it was found that the uneven distribution of water also affects the mechanical properties of coal. This was verified in the local strain and acoustic emission characteristics of coal specimens.