# Laboratory Tests on Swelling Properties of Field-Coring Gypsum Rock in Tunnels
## 4 Results and Discussion
### Free-Swelling Ratio  
The test results of free-swelling ratio are listed in Table 2 and plotted in Figure 7a-c, respectively. It can be seen from Figure 7a-c that the variations with time of the free-swelling ratios of the three samples are similar. It can be seen from Figure 7a that, during the first 120 min, the free-swelling ratios of the radial direction 1, the radial direction 2 and the axial direction of the samples PA-1, PA-2 and PA-3 all increase rapidly as the immersion time increases. Radial direction 1 represents the sum of the numerical changes in dial indicators 1 and 3, while radial direction 2 represents the other direction. The axial-direction swelling ratio is calculated by dial indicator 5, as shown in Figure 4. After the first 120 min, the free-swelling ratios of radial direction 1, radial direction 2 and the axial direction increase slowly as the immersion time increases. Similar to previous research, the largest value of the free-swelling ratios of radial directions 1 and 2 is defined as the maximum radial free-swelling ratio, which is used to show the free-swelling behavior parallel to the gypsum layer. In order to further understand the maximum radial free-swelling deformation and axial free-swelling deformation of gypsum rock, the average value of the maximum radial \begin{table}
\begin{tabular}{c c c c} \hline  & **Radial Direction 1** & **Radial Direction 2** & **Axial Direction** \\  & **Swelling Ratio in the** & **Swelling Ratio in the** & **Swelling Ratio in the** \\  & **2880 th Minute (\%)** & **2880 th Minute (\%)** & **2880 th Minute (\%)** \\ \hline PA-1 & 10.86 & 4.53 & 6.02 \\ PA-2 & 14.50 & 4.94 & 5.71 \\ PA-3 & 12.10 & 6.82 & 7.03 \\ \hline \end{tabular}
\end{table} 
Table 2: Free-swelling ratio. Figure 7: Free-swelling ratio: (**a**) Sample 1; (**b**) Sample 2; (**c**) Sample 3.  
free-swelling ratio is achieved as shown in Figure 8. The average value of the axial free-swelling ratio is achieved as shown in Figure 9.  
Figure 8 shows the maximum radial free-swelling ratio variation as time increases. It can be seen from Figure 8a that there is an inflection point when the maximum radial free-swelling ratio increases as time increases (t = 120 min in the present study). Before the inflection point, the maximum radial free-swelling ratio increases rapidly with the increase in immersion time. After the inflection point, the maximum radial free-swelling ratio becomes stable as immersion time further increases. The maximum radial free-swelling ratio at the inflection point is about 70.0% of the maximum radial free-swelling ratio at 2880 min. Figure 8b shows the relationship between the maximum radial free-swelling ratio and the time for the first 120 min. It can be seen from Figure 8b that, as immersion time increases, the radial free-swelling ratio increases slowly at first, then rapidly, and then becomes slow again in the final period. The radial free-swelling ratio shows as an S-shaped increase trend with the increase in immersion time. The maximum radial free-swelling ratio reached 8.83% during the first 120 min. Figure 9a shows the variation in axial free-swelling ratio with time. During the first 120 min, the axial free-swelling ratio increases rapidly with the increase in immersion time. Figure 8: Maximum radial free-swelling ratio. Relationship between the maximum radial free-swelling ratio and time for (**a**) 2880 min and (**b**) during the first 120 min. Figure 9: Axial free-swelling ratio. Variation in axial free-swelling ratio for (**a**) 2880 min and (**b**) during the first 120 min. After 120 min, the axial free-swelling ratio increases slowly with the increase in immersion time. The maximum axial free-swelling ratio after immersion for 2880 min reaches 6.26%. Figure 8(b) shows the variation in axial free-swelling ratio for the first 120 min. The axial free-swelling ratio also shows an S-shaped increasing tendency. The axial free-swelling ratio increases slowly at first, then rapidly, and slowly again later on.