## 3 Hydration Absorption Deformation Characteristics of Outcrop Porous Sandstone
### Automatic Shooting Detection Device and Detection Scheme
#### 3.3.1 Displacement Field and Variation Curve  
Sandstone samples 1 and 3 were used for analysis, and the displacement field of the sample surface at different hydration absorption times was obtained. The samples produced horizontal displacement (\(U\)(mm)) and vertical displacement (\(V\)(mm)) after hydration absorption, which is caused by the expansion of pore hydration absorption. The horizontal displacement field at a different time is shown in Figures 18 and 19. By observing the displacement cloud diagram of sandstone sample 1, it was found that the horizontal displacement of the sample after hydration absorption is not uniform. The specific performance is that the displacement of the upper half is larger than that of the lower half, and the left half is dominated by negative displacement, while the right half domain is dominated by positive displacement. There is almost no displacement in the middle domain, which is due to the constraint effect in the middle of the sample. The displacement cloud diagram of sandstone sample 3 reveals a notable disparity between the upper and lower halves, with greater displacement observed in the former. Negative displacement prevails in the left domain, while the middle and right domains predominantly exhibit positive displacement. The analysis shows that the horizontal displacement cloud diagram of sandstone sample 1 is more in line with the actual situation of sandstone hydration absorption and expansion.  
The horizontal average displacement curve at a different time is shown in Figure 20. It can be seen that the sample will have a large displacement at the beginning, and with the increase in time, the horizontal displacement of the sample increases gradually, and finally tends to be constant. The two curves better reflect the horizontal average displacement characteristics of sandstone after hydration absorption and expansion.  
Figure 17: The equipment conditions and images taken using the camera of Test 3.  
Figure 19: Horizontal displacement field of sandstone sample 3 at a different time.  
Figure 18: Horizontal displacement field of sandstone sample 1 at a different time.  
The vertical displacement fields at different moments are shown in Figures 21 and 22. By observing the displacement cloud diagram of sandstone sample 1, it is found that the vertical displacement of the sample after hydration absorption is not uniform. The specific performance is that the displacement of the upper half is larger than that of the lower half. The upper half is dominated by negative displacement, and the lower half is dominated by positive displacement. There is almost no displacement in the middle-down regions. The displacement cloud diagram of sandstone sample 3 shows that the inhomogeneity of vertical displacement is low. In the initial stage, the displacement of the upper right corner surpasses that of the upper left corner. In subsequent stages, the displacement of the lower left corner surpasses that of the upper right corner, indicating that the displacement of the upper part of the whole is greater than that of the lower part.  
Figure 20: Horizontal average displacement curve.  
Figure 21: Vertical displacement field of sandstone sample 1 at different time.  
Figure 22: Vertical displacement field of sandstone sample 3 at a different time.  
The vertical average displacement curve is shown in Figure 23. It can be seen that the sandstone sample 3 will produce a large displacement at the beginning. With the increase in time, the vertical displacement of the sample gradually flattens out, and finally tends to be constant, which better reflects the characteristics of the vertical average displacement of sandstone after hydration absorption and expansion. The vertical average displacement curve of sandstone sample 1 is tortuous and the error is large, so the law cannot be obtained. It is believed that the error is caused by the poor sample speckle quality.